Chapter 1: IMPORTANCE OF POST HARVEST TECHNOLOGY OF HORTICULTURAL CROPS

• Development of natural food columns, fiber, single cell protein and food grade enzymes from processing wastes will be useful.

• www. Postharvest.ucdavis.edu
• www.postharvest.ifsa.ufl.edu
• www.fao.org

Lecture 2: MATURITY INDICES, HARVESTING AND POST HARVEST HANDLING OF FRUITS AND VEGETABLES I. MATURITY

1. Visual indices

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MATURITY AND RIPENING PROCESS – MATURITY

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Factors affecting ripening can be physiological, physical, or biotic.
Physiological factors relate to fruit maturity or environmental factors, which affect the metabolism of fruit and banana.
Physical factors include mechanical damage, or relate to dimensions of the fruit.
Biotic factors include attack from pests and diseases.
Fruit maturity. The more mature fruit is at harvest, the shorter the ripening period. Studies show that banana harvested 100 days after flowering ripened in 11 days. When the same cultivar was harvested 90 days after flowering, the ripening period increased to 15 days, and further increased to 22 days when the fruit was harvested at 80 days. Farmers have to match the date of harvest with the transportation time to the market. However, an early harvest reduces yield.

As fruits mature, the cross-sectional diameter increases. Fruit angularity also changes during growth and maturation. As fruits approach full maturity, fruit angles become less acute Fruit angularity can be used to predict the optimum harvest date of banana.
Temperature. Physiological studies on bananas show that storage life decreases as external temperature increases over the range 15-35ºC. A 1ºC reduction increases storage period by 1-2 days.
The relationship between ripening period and temperature is due to fruit respiration. Fruit respiration depends on many enzymatic reactions, and the rate of these reactions increases exponentially with increase in temperature. Studies show that ripe fruits respire at approximately 4 times the rate of unripe fruits. Consequently, ripe fruits lose sugar resources at a higher rate than unripe fruits. This explains why ripe fruits deteriorate quickly.
The relationship between temperature and respiration is described mathematically by van’t Hoff’s temperature quotient (Q10). van’t Hoff showed that the rate of respiration approximately doubles for each 10ºC rise in temperature.
Water loss and humidity. Where fruit is sold on a weight basis, loss of water means economic loss. Additionally, water loss reduces visual quality. Water loss causes fruit to lose its firmness, the peel becomes soft and shriveled, and ripening period reduces. Studies on fruits show a curvilinear or power relationship between fruit weight loss and ripening period. For a 2% change from 2% to 4% weight loss per day, ripening period reduced by 9 days or 50%. Therefore, at a low rate of weight loss, a small increase in weight loss has a critical effect on ripening.
The rate of water loss depends on the ambient relative humidity (RH). RH is the amount of water vapor present in the air, relative to the maximum amount of water vapor that can be held in the air, at a given temperature, saturated air being 100% RH. When a water-containing material such as fruit is placed in an enclosed space, for example, a sealed container, the water content of the air within the container increases or decreases until it is in equilibrium with the fruit.
The water equilibrium principle applies when fruit is stored. The rate of water loss depends on the ambient RH. At an ambient RH of 95-100%, fruit loses little or no moisture, and ripening period is unaffected. However, as humidity decreases, the rate of water loss increases, and ripening period reduces.
Excessive wetting can also be a problem. When fruit is stored in wet conditions, such as in moist coir (coconut fiber), the uptake of water from the coir to the fruit leads to peel splitting.
Sunlight. Exposure to direct sunlight reduces the ripening period of fruits. Sunlight increases fruit temperature above ambient temperature, which increases respiration, and possibly the rate of water loss. The solar radiation that falls upon foods held in direct sunlight increases the temperature above the ambient temperature. The amount of increase in temperature depends on the intensity of the radiation, the size and shape of the food’ and the duration of exposure to the direct rays of the sun. The intensity of solar radiation depends upon latitude, altitude, season of the year, time of day, and degree of cloud cover.
Altitude. Within a given latitude the prevailing temperature is dependent upon the elevation when other factors are equal. There is on the average a drop in temperature of 6.5°C for each Km increase in elevation above sea level. Storing food at high altitudes will therefore tend to increase the storage life and decrease the losses in food provided it is kept out of the direct rays of the sun.

Atmosphere. The normal atmosphere contains by volume, approximately 78% nitrogen, 21% oxygen, 1% argon, 0.03% carbon dioxide’ various amounts of water vapor and traces of inert gases. Modifying the atmosphere can improve the shelf life and reduce wastage of certain foods.
One type of controlled atmosphere storage (CA) is refrigerated storage in which the level of oxygen is reduced to about 3% with the carbon dioxide content being raised to 1 to 5%, depending on the commodity. This CA storage may double the storage life over that of regular cold storage for certain varieties of apples and pears by slowing down the natural rate of respiration.
Ethylene (C2H4) is a gaseous plant hormone which determines the time between harvest and senescence. The time from harvest to the climacteric respiratory response is called the ‘green life’ or preclimacteric period. Ethylene shortens the preclimacteric period; at high concentrations, ethylene causes rapid initiation of the climacteric respiratory response and accelerates ripening.
When nonclimacteric fruits are exposed to ethylene, fruits show an increased rate of respiration. However, respiration rate falls when ethylene is removed. A rise in respiration rate may occur more than once in nonclimacteric fruits. However, for climacteric fruits, the climacteric is autocatalytic, that is, once started, the process cannot be stopped until the fruit is ripe.
Poor storage methods allow a build up of ethylene, stimulate the climacteric response, and reduce the ripening period. For example, plastic sheets placed over stacks of fruit for shade increase the level of ethylene within the fruit stack and increase the rate of ripening. Therefore, store fruit in thatched or ventilated areas to prevent the build up of ethylene. Also, do not store unripe fruits with ripe fruits.
During the preclimacteric period, fruits are less susceptible to physical damage and pathological attack. This is the best time for handling, transportation, and marketing.
Mechanical damage. Mechanical damage is a physical factor affecting ripening. Fruit damage during handling generates ethylene. If ethylene production is sufficient to start the climacteric respiratory response, fruit immediately starts to ripen.
Damage can also reduce ripening period by causing moisture loss. The effect of damage can easily be measured by recording fruit weight loss over time. Cuts and abrasions on the surface membrane cause the most weight loss.
After harvest, fruits lose the ability to repair ruptured peel. Harvesting techniques which damage fruit reduce storability.
Studies show that an abrasion affecting 5-10% of the peel can reduce the ripening period by 40%. Damage can also lead to secondary infection, which increases the rate of water loss and further reduces quality.
Surface to volume ratio. The ratio between surface area and volume determines the rate of water loss. The greater the surface to volume ratio, the shorter the postharvest life. A leaf which has two large surfaces with little volume loses moisture faster than a fruit. Large fruits lose less water than small fruits.
Peel thickness. Fruits with thin peel lose more water. A higher peel permeability leads to a higher rate of water loss and a faster ripening rate. Also, fruits with thick peel, for example melons, withstand damage better than fruits with thin peel, such as tomatoes.
Stomatal density. A higher density of stomata may cause a higher rate of water loss, which accelerates ripening.
Biotic stress. Fungi, bacteria, viruses, and insects also account for a considerable proportion of total postharvest loss. Pests and diseases reduce both ripening period and overall quality. However, attack by pests and diseases is often secondary because a pest exploits a damaged area of the fruit. Careful fruit handling often prevents such attacks.

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Chapter 5: PRE HARVEST FACTORS AFFECTING QUALITY ON POST HARVEST LIFE OF FRUITS AND VEGETABLES – FACTORS RESPONSIBLE FOR DETERIORATION OF HARVESTED FRUITS AND VEGETABLES

Quality of post harvest product
Post harvest quality represents market quality, edible quality, transport quality, table quality, nutritional quality, internal quality and appearance quality. Quality means a combination of characteristics, attributes and properties that gives the values to human and enjoyments. Consumers consider good quality in relation to colour, flavour and nutrition. Quality of the produce is the final manifestation of inter-relation between the commodity and its environment. The genetic characteristics and physiological status of the commodity determine the typical post-harvest behavior and quality of the produce and these two are the major bases for the interaction. Pre-harvest factors viz, environmental factors such as temperature, relative humidity, water potential, light, cultural practices and pest management techniques determined the inherent quality of the produce. However, the ultimate quality is the final manifestation of inter relation between the commodity and its environment.
Several pre-harvest and post-harvest factors affect the quality of horticultural crops. Some of these factors are related to plant, others are related to environment or to cultural practices.
A. Pre-harvest factors
a) Related to plants

1. Crops: Quality of the fruit and vegetables are varies from crop to crop e.g. jackfruit, bael, potato, onion, pumpkin, garlic etc. having good quality in relation to shelf life, while apple, mango, cherry, strawberry, tomato, capsicum, okra, brussels sprout, chinese cabbage, carrot, radish attract more to consumers due to their attractive appearance.
2. Cultivars: The quality of seed or plant material is an important factor that controls the quality of the fruit and vegetable produced. Several parameters of quality are controlled genetically.

• Cultural practices: All cultural practices have direct effect on the final quality of the produce.
• Planting period: Many plants are very sensitive to environmental conditions, and thus quality will not be optimized when crop is produced under adverse conditions. Producing summer plants during the winter or vice-versa will not be appropriate, unless protection practices are implemented.
• Planting density: It affects both the quantity and quality of the produce. High density planting increases competition between plants, reduces light availability, and thus may decrease quantity. Low density planting lead to large size, better colored fruit or vegetable which may have shorter shelf life. Larger fruits are commonly more sensitive to physiological disorders.
• Irrigation: Irregular watering usually reduces fruit size, increases splitting, physiological disorders, reduces water content in the plant or plant part, etc.
• Fertilization: Poor management of fertilizers will increase physiological disorders due to deficiencies of some minerals or increase of other leading to toxicity. In both cases, quality will be negatively affected.
• Pruning: It reduces the load and increases the growth of fruit and chemical use after harvest.
• Thinning: This operation reduces the competition between fruits or plants and thus promotes a good balance between the vegetative and fruit parts and improves quality.
• Protection: Pathogens and insects have a very negative effect on quality. Poor management of plant protection programmes can lead to very poor quality and reduced yield.
b) Related to environments
Temperature is the most important environmental factor that affects quality, very low or very high temperature may injure sensitive crops. Adequate high intensity and quality is important for the formation of some colour. Wind and rain may cause negative effects on some crops.
c) Related to chemicals
Many hormones and growth regulators are used in agriculture and they can affect quality in different ways.
B) During harvest factor
• Season: Quality of produce are greatly influenced by season e.g. Winter season harvest having more shelf life as compared to other season, while off season fruits and vegetables give more remunerative price. Harvesting during or immediately after rains should not be carried out since it creates most favourable conditions for multiplication of micro-organisms. Citrus fruits become susceptible to damage if harvested during rains as their rind becomes turgid and prone to easy bruising, sun-scald etc.
• Time: Fruits and vegetables should always be harvested when temperature is mild. Because, higher temperature leads to faster respiration. Morning harvest of horticultural crop prefer for local market because they are fully fresh and turgid and having dew drop in this time. Evening harvesting is preferred for distant market due to higher accumulation of reserved carbohydrates and less amount of moisture which give the better quality of the produce to consumer. Leafy vegetables harvested in the latter part of the morning or late in the afternoon, the petioles of these vegetables break less easily and their leaves are more resistant to tearing, since they have lost water through transpiration and therefore are less brittle. Cucumber is harvested in the late morning when it to be transported under less than ideal condition because it is less prone to injury when it contains less water.
• Method of harvesting: Selection of suitable method for harvesting of the produce is necessary otherwise bruises or injuries during harvesting may later manifest as black or brown patches making them unattractive. Latex coming out of stem in mango should not be allowed to fall on fruits as it creates a black spot. Injury to peel may become an entry point for microorganisms, causing rotting. Some harvesting gadgets have been developed, e.g. mango harvester in Lucknow (CISH).
• Stage of harvesting: Fruits and vegetables must be harvested at right stage of maturity. A very common cause of poor product quality at harvest and rapid deterioration thereafter is harvesting immature vegetables. Vegetables harvested immature or over mature usually do not keep long. Fruit vegetables harvested too early lose water fast and are more susceptible to mechanical damage and microbial attack. An over mature vegetable is more susceptible to decay, has passed its best eating quality, and deteriorates fast.
• Consumer demand: Harvesting time and harvest maturity can be altered by the requirement of the consumer’s demand which may affect the quality of the produce at some extent.
c) Post-harvest factors:
• Curing: Curing is done immediately after harvesting. It strengthens the skin. The process is induced at relatively higher temperature and humidity, involving suberization of outer tissues followed by the development of wound periderm which acts as an effective barrier against infection and water loss. It is favoured by high temperature and high humidity. Potato, sweet potato, colocasia, onion and garlic are cured prior to storage or marketing. Potato tubers are held at 18°C for 2 days and then at 7°—10°C for 10—12 days at 90% relative humidity. Curing also reduces the moisture content especially in onion and garlic. Drying of superficial leaves of onion bulbs protects them from microbial infection in storage.
• Degreening: It is the process of decomposing green pigment (Chlorophyll) in fruits usually applying ethylene or similar metabolic inducers to fruit. It is applicable to banana, citrus and tomato. Degreening is carried out in special treating rooms with controlled temperature and humidity in which low concentration of ethylene (20 ppm) is applied.
• Pre-cooling: High temperatures are detrimental to keeping quality of fruits and vegetables, especially when harvesting is done during hot days. Pre-cooling is a means of removing the field heat. It slows down the rate of respiration, minimizes susceptibility to attack of micro-organisms, and reduces water loss. Peas and okra which deteriorate fast need prompt pre-cooling.

1. Washing and drying: Most of the fruits and vegetables are washed after harvesting to improve their appearance, to prevent wilting and to remove primary inoculum load of microorganism. Hence, a fungicide/bactericide should be used in washing water. Washing, improves shelf life of bananas by delaying their ripening. After washing, excess of water should be removed which would otherwise encourage microbial spoilage.

• Sorting and grading: Fruits and vegetables require sorting and grading for uniform packing at field level. Sorting is done on the basis of size and colour while grading practice is performed as per the defect or on the basis of marketable and unmarketable produce.
• Disinfection: Papaya, mango, melon and other fruits are susceptible to fruit fly attack. Disinfection is done either by vapour heat treatment (VHT) at 43°C with saturated air with water vapour for 6-8 hr by Ethylene dibromide fumigation.
• Waxing: Fruits and vegetables have a natural layer on their outer surface which is partly removed by washing. An extra discontinuous layer of wax applied artificially with sufficient thickness and consistency to prevent anaerobic condition within the fruits provides necessary protection against decay organism. Waxing also improves the appearance and glossiness, making them more acceptable.
• Packing: It means more than carrying multiples of an object. Packing not only protects the horticultural produce but also makes a favourable impression on the buyers and May able to fetch higher income.
• Delivery: Moving the harvest produce from the farm to the customer in good condition is important. All efforts upto delivery can be invalid if the fresh fruits and vegetables reach the destination in poor condition. Care should be taken to protect the produce and it becomes necessary when mixing load of fruits and vegetables to prevent violating the compatibility factors.

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A- Primary causes of loss: Those are directly affect the food 
2.1- Enzymic changes
     Enzymes which are endogenous to plant tissues can have undesirable or  desirable consequences.
Examples involving enzymic changes include:
2.1.1- the post-harvest spoilage of fruit and vegetables
2.1.2- oxidation of phenolic substances in plant tissues by phenolase (leading to   browning)
2.1.3- sugar – starch conversion in plant tissues by amylases
2.1.4- post-harvest demethylation of pectic substances in plant tissues (leading to softening of plant tissues during ripening, and firming of plant tissues during   processing).
     The major factors useful in controlling enzyme activity are:

1. temperature
2. water activity
3. pH
4. chemicals which can inhibit enzyme action

2.2- Chemical changes
2.2.1- Sensory quality
The two major chemical changes which occur during the processing and  storage of foods and lead to a deterioration in sensory quality are lipid oxidation and non-enzymatic browning. Chemical reactions are also responsible for changes in the colour and flavour of foods during processing and storage.
2.2.1.1- Lipid oxidation rate and course of reaction is influenced by light, local   oxygen concentration, high temperature, the presence of catalysts (generally transition metals such as iron and copper) and water activity. Control of these factors can significantly reduce the extent of lipid oxidation in foods.
2.2.1.2- Non-enzymic browning is one of the major causes of deterioration which occurs during storage of dried and concentrated foods.

2.2.1.3- Colour changes
Almost any type of food processing or storage causes some deterioration of the chlorophyll pigments. This reaction is accelerated by heat and is acid catalysed.
2.2.1.4- Flavour changes
In fruit and vegetables, enzymically generated compounds derived from     long-chain fatty acids play an extremely important role in the formation of characteristic flavors. In addition, these types of reactions can lead to significant off-flavors. 
The permeability of packaging materials is of importance in retaining     desirable volatile components within packages, or in permitting undesirable  components to permeate through the package from the ambient atmosphere.

2.2.2- Nutritional quality
The four major factors which affect nutrient degradation and can be    controlled to varying extents by packaging are

1. light
2. oxygen concentration
3. temperature
4. water activity.

2.3- Physical changes
One major undesirable physical change in food is the absorption of moisture as a consequence of an inadequate barrier provided by the package; this results in caking. It can occur either as a result of a poor selection of packaging material in the first place, or failure of the package integrity during storage. In general, moisture absorption is associated with increased cohesiveness.

2.4- Biological changes
2.4.1- Microbiological
Micro-organisms can make both desirable and undesirable changes to the quality of foods depending on whether or not they are introduced as an essential part of the food preservation process or arise unintentionally and subsequently grow to produce food spoilage.
The two major groups of micro-organisms found in foods are bacteria and fungi, the latter consisting of yeasts and moulds. Bacteria are generally the fastest growing, so that in conditions favourable to both, bacteria will usually outgrow fungi.
Foods are frequently classified on the basis of their stability as non-perishable, semi-perishable and perishable.
The protection of packaged food from contamination or attack by micro-organisms depends on the mechanical integrity of the package (e.g. the absence of breaks and seal imperfections), and on the resistance of the package to penetration by micro-organisms.

2.4.2- Macrobiological
2.4.2.1 Insect Pests
Warm humid environments promote insect growth, although most insects will not breed if the temperature exceeds about 35 C° or falls below 10 C°. Also many insects cannot reproduce satisfactorily unless the moisture content of their food is greater than about 11%.
2.4.2.2 Rodents
Rats and mice carry disease-producing organisms on their feet and/or in their intestinal tracts and are known to harbour salmonella of serotypes frequently associated with food-borne infections in humans.
B- Secondary causes of loss: Those lead to conditions that encourage a primary cause of loss such as:
1- Inadequate harvesting, packaging and handling skills.
2- Lack of adequate containers for the transport and handling of perishables.
3- Storage facilities inadequate to protect the food.
4- Transportation inadequate to move the food to market before it spoils.
5- Inadequate refrigerated storage.
6- Inadequate drying equipment or poor drying season.
7- traditional processing and marketing systems can be responsible for high losses.
8- Legal standards can affect the retention or rejection of food for human use.
10- Knowledge of management is essential for maintaining tool  
in good condition during marketing and storage.
11- Bumper crops can overload the post-harvest handling system or exceed the  consumption need and cause excessive wastage.

3- Sites of losses
Losses may occur anywhere from the point where the food has been harvested or gathered up to the point of consumption. Losses can occur during one of the following processes:
1- Harvest. The separation of the commodity from the plant that produced it.
2- Preparation. The preliminary separation or extraction of the edible from the non- edible portion.
3- Preservation. The prevention of lose and spoilage of foods. For example, the sun-drying of fruit, the use of refrigeration and the use of fungicides to inhibit mold growth in fruits.
4- Processing. The conversion of edible food into another form more acceptable or more convenient to the consumer, for example, the manufacture of fruit juice and the canning of fruits and vegetables.
5- Storage. The holding of foods until consumption. Most storage is common storage (ambient temperature) but there are extensive storage capacities that can hold food under refrigerated or controlled atmosphere conditions.
6- Transportation. All forms of transportation are used to convey foods from the point of production to the ultimate point of consumption.

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Chapter 8: Methods of storage-precooling, pre storage treatments, low temperature storage, controlled atmosphere storage, hypobaric storage, irradiation and low cost storage structures

1. inhibiting the growth of decay producing microorganisms
2.  restricting enzymatic and respiratory activity
3.  inhibiting water loss
4.  reducing ethylene production

1. Room cooling
2. Forced-air cooling
3. Hydro-cooling
4. Ice cooling
5. Vacuum cooling
6. Cryogenic cooling
7. Evaporative cooling

Cold Wall

• Ibrahim Dincer. (1995). Air Flow Precooling of Individual Grapes. Journal of Food Engineering, 26, 243-240.
• Barbara Teruel; Theo Kieckbusch; Luis Cortez. (2004). COOLING PARAMETERS FOR FRUITS AND VEGETABLES OF DIFFERENT SIZES IN A HYDROCOOLING SYSTEM. Sci. Agric. (Piracicaba, Braz.), v.61, n.6, p.655-658.
• James F. Thompson, F.Gordon Mitchell, and Robert F. Kasmire. Cooling horticultural commodities in Postharvest technology of horticultural crops, Third Edition, (2002). University of California, Agriculture and Natural Resources. pp 97-112.
• Jennifer R. DeEll ; Clement Vigneault ; Stephanie Lemerre.(2000). Water temperature for hydrocooling field cucumbers in relation to chilling injury during storage. Postharvest Biology and Technology, 18 ,27–32.
• Tadhg Brosnan; Da-Wen Sun. (2001). Precooling techniques and applications for horticultural products – a review. International Journal of Refrigeration, 24, 154-170.
• www.oznet.ksu.edu/library/hort2/samplers/mf1002.asp
• www.omafra.gov.on.ca/english/engineer/facts/98-031.htm
• www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex7463
• usna.usda.gov/hb66/011precooling.pdf
• www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-5/index.html.

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Chapter 9: Various methods of packaging- packaging materials and transport

1. CFB Boxes

1. Light in weight
2. Reasonably strong
3. Flexibility of shape and size
4. Easy to store and use
5. Good pointing capability
6. Economical
7. Wooden Boxes

1. Sacks

1. 1. Labour cost in handling is greatly reduced.
   2. Transport cost may be reduced.
   3. Goods are protected and damage reduced.
   4. Mechanized handling can be very rapid.
   5. Through high stacking, storage space can be more efficiently used.
   6. Pallets encourage the introduction of standard package sizes.

1. Gorden L.Robertson. 2003. Food Packaging Principles and Practices. Marcel and Deckker, Inc., New York
2. NIIR Board. 2000. Hand book on modern packaging industries. Asia Pacific Press Inc. Delhi, India
3. M.Mahadevah and R.V.Gowramma.1996. Food Packaging Materials. Tata- McGraw – Hill Pub. Company, Limited, New Delhi.
4. Crosby N.T. 1981. Food packaging materials. Applied Science Publishers Ltd., New york
5. Heiss, R.1970. Principles of food packaging. An International guide. P.Keppler Verlag KG, Heusenstamn, Germany.
6. Paine and Paine.1983. Hand book of food packaging. Blackie and Son Ltd., London
7. Wilmer A.Jenkeins and James P.Harrington. 1991. Packaging foods with plastics. Technomic publishing company, Inc., Pennsylvania, USA.

1. Journal of Food Science and technology
2. Indian Food packer
3. Indian Food Industries
4. Food and pack

1. http://www.bharatbook.com/general/Food_Packaging.asp
2. http://books.google.co.in/books?id=wMfOX6FgIJoC&pg=PA74&lpg=PA74&dq=food+packaging&source
3. http://www.foodproductiondaily.com/

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Packing Technology & Machinery

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IMPORTANCE AND SCOPE OF FRUIT AND VEGETABLE PRESERVATION IN INDIA

Fruits and vegetables are an important supplement to the human diet as they provide the essential minerals, vitamins and fibre required for maintaining health. In India, the total fruits and vegetable production is about 137 million tonnes per year i.e. 46 MT fruits and 92 MT vegetables. The varied agro climatic conditions available in our country make it possible for us to produce several types of tropical, subtropical and temperate fruits and vegetables. It has been variously estimated that 20 to 30% of the horticultural produce is lost before consumption which accounts for Rs. 5000 crores because of poor harvesting, handling, storage, transportation and marketing practices. The fruits and vegetables are highly perishable commodities and the ambient high temperature obtained in the tropical country like ours makes them more susceptible for rapid development of senescence, decay and rotting. Both respiratory and transpiratory rates are proportional to temperature, increases and so that the produce quickly dries, wilts and spoils unless properly preserved.     
            Two approaches are possible for solving this problem. One is the creation / expansion of cold storage facilities in the fruit and vegetable producing regions themselves, as also in the major urban consumption centres, to ensure supply of fresh fruits and vegetables throughout the year. Another approach is to process the fruits and vegetables into various products which could be preserved for a long time and add to the value of the product. With increasing urbanization rise in middle class purchasing power, change in food habits and the dyeing out of the practice of making preserves in individual homes, there is increasing demands for factory made jams, jellies, fruit beverages, dehydrated foods, pickles etc. in the domestic market. Moreover, there is considerable demand for some of these products in foreign markets e.g. mangoes both fresh and canned, fruit juices, salted cashew are good foreign exchange earners.   
            The production of fruit and vegetable products in India are canned, bottled fruits and vegetables, jams, jellies, marmalades, fruit juices, fruit pulps, squashes, crashes, cordials, fruit syrups, fruit nectars, RTS fruit beverages, fruit juice concentrates, chutneys, pickles, mango slices in brine preserves, candied and crystallized fruits and peels, dehydrated fruits and vegetables, frozen fruits and vegetables, tomato products, sauces, soups etc.
            In India there are 4000 processing industries are functioning. But a marginal quantity of 1.0 to 2.0 % of the produce is processed and packaged in contrast with developed and developing countries i.e., 70 to 80%. The total annual consumption of processed fruits and vegetable products in the country is rockened at only 50,000 tonnes of which defence and star hotels account for 15,000 tonnes and the remaining 35,000 tonnes to the public, i.e. a percapita consumption of 40 gms / year. Thus we can see on enormous scope and potential for the expansion of fruits and vegetable industries in India in the future.
Export of fruits and vegetables from India
            In terms of global trade, India’s share in agricultural export is insignificant. While India contributes 8.56% and 13.5% respectively to world’s fruits and vegetables production, its share in global exports of these products is less than 1.0%. Delhi, Bombay and Trivandrum are the three main parts for air freighting of fruits and vegetables. These are mainly exported to Kuwait, Dubai and Saudi Arbia. Grapes are exported in large quantities from Bombay during January to March, while mango is exported during April to June. West Asia, the Far East and West Europe are the main export markets for Indian fruits and vegetables. Fruits juices, fruit pulp and pickles are mainly imported by the USSR, Yemen, Arab Republic. The other markets for processed fruits are UK, UAE, Saudi Arabia, Kuwait, Germany, USA, Holland and Switzerland. Nearly half of India’s processed fruit exports are mango based fruit juice, canned and bottled fruits.
            Fresh onions and mangoes are the main commodities entering in export trade. The other important fruits exported are melon, sweet melon, grapes, pomegranate, sapota, custard apple, orange, papaya, pineapple. Among other vegetables the principal items are tomato, ladies finger bitter gourd, chillies, fresh beans, cabbage, brinjal etc.   

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PRINCIPLES OF PRESERVATION BY HEAT, LOW TEMPERATURE, CHEMICALS AND FERMENTATION
PRINCIPLES OF FOOD PRESERVATION BY HEAT

Application of heat to the foods leads to the destruction of microorganisms. The specific treatment varies with:
i)   The organisms that has to be killed.
ii)  The nature of the food to be preserved and
iii) Other means of preservation that may be used in addition to high temperature.

 High temperatures used for preservation are usually: (1) Pasteurization temperature – below 100oC (2) Heating at about 100oC and (3) Sterilization temperature above 100oC.
a. Pasteurization–below 100oC              ­
            Pasteurization is a heat treatment that kills part but not all the microorganisms present and the temperature applied is below 100oC. The heating may be by means of steam, hot H2O, dry heat or electric currents and the products are cooled promptly after the heat treatments. The surviving microorganisms are inhibited by low temperature (or) some other preservative method if spoilage is to be prevented.
            Preservative methods used to supplement pasteurization include                         (i) refrigeration e.g. of milk (2) keeping out microorganisms usually by packaging the product in a sealed container (3) maintenance of anaerobic conditions as in evacuated, sealed containers (4) addition of high concentration of sugar, as in sweetened condensed milk and (5) presence (or) addition of chemical preservatives e.g. the organic acids on pickles.   
Methods of pasteurization            
HTST method – High temperature and short time (above 70oC)
LTH method   – Low temperature and higher time (or) Holding method (60-70oC)
b. Heating at about 100oC
            A temperature of approximately 100oC is obtained by boiling a liquid food, by immersion of the container of food in boiling water or by exposure to flowing steam. Some very acid foods, e.g., sauerkraut may be preheated to a temperature somewhat below 100oC, packaged hot, and not further heat processed. Blanching fresh vegetables before freezing or drying involves heating briefly at about 100oC.
c. Sterilization-above 100oC
            By this method all microorganisms are completely destroyed due to high temperature. The time and temperature, necessary for sterilization vary with the type of food. Temperatures above 100oC can only be obtained by using steam pressure sterilizers such as pressure cookers and autoclaves.
            Fruits and tomato products should be noted at 100oC for 30 min. so that the spore-forming bacteria which are sensitive to high acidity may be completely killed. Vegetables like green peas, okra, beans, etc. being non acidic and containing more starch than sugar, require higher temperature to kill the spore forming organisms. Continuous heating for 30-90 min. at 116oC is essential for their sterilization. Before using, empty cans and bottles should also be sterilized for about 30 min. by placing them in boiling water.
Difference between pasteurization and sterilization

Aseptic canning
            It is a technique in which food is sterilized outside the can and then aseptically placed in previously sterilized cans which are subsequently sealed in an aseptic environment.
Hot Pack (or) Hot fill
            Filling of previously pasteurized or sterilized foods, while still hot, into clean but not necessarily sterile containers, under clean but not necessarily aseptic conditions.
PRESERVATION BY LOW TEMPERATURE
            Microbial growth and enzyme reactions are retarded in foods stored at low temperature. The lower the temperature, the greater the retardation. Low temperature can be produced by
(a)   Cellar storage (about 15oC)
            The temperature in cellar (underground rooms) where surplus food is stored in many villages is usually not much below that of the outside air and is seldom lower than 15oC. It is not enough to prevent the action of many spoilage organisms or of plant enzymes. Root crops, potatoes, cabbage, apples, onions and similar foods can be stored for limited periods during the winter months.
(b)  Refrigerated (or) chilling (0 to 5oC)

            Chilling temperature are obtained and maintained by means of ice or mechanical refrigeration. It may be used as the main preservative method for foods or for temporary preservation until some other preservative process is applied. Most perishable foods, including eggs, dairy products, meats, sea foods, vegetables and fruits, may be held in chilling storage for

a limited time with little change from their original condition. Enzymatic and microbial changes in the foods are not prevented but are slowed considerably.
            Factors to be considered in connection with chilling storage include the temperature of chilling, the relative humidity, air velocity and composition of the atmosphere in the store room, and the possible use of ultra violet rays or other radiations.    
PRESERVATION BY CHEMICALS
            A preservative is defined as only substance which is capable of inhibiting, retarding or arresting the growth of microorganisms.
Microbial spoilage of food products is also controlled by using chemical preservatives. The inhibitory action of preservatives is due to their interfering with the mechanism of cell division, permeability of cell membrane and activity of enzymes.
Pasteurized squashes, cordials and crushes have a cooked flavour. After the container is opened, they ferment and spoil within a short period, particularly in a tropical climate.  To avoid this, it is necessary to use chemical preservatives. Chemically preserved squashes and crushes can be kept for a fairly long time even after opening the seal of the bottle. It is however, essential that the use of chemicals is properly controlled, as their indiscriminate use is likely to be harmful. The preservative used should not be injurious to health and should be non-irritant. It should be easy to detect and estimate.
Two important chemical preservatives are permitted to beverages according to the FPO (1955).
1. Sulphur dioxide and
2. Benzoic acid
Sulphur dioxide
            It is widely used throughout the world in the preservation of juice, pulp, nectar, squash, crush, cordial and other products. It has good preserving action against bacteria and moulds and inhibits enzymes, etc.  In addition, it acts as an antioxidant and bleaching agent. These properties help in the retention of ascorbic acid, carotene and other oxidizable compounds. It also retards the development of nonenzymatic browning or discolouration of the product. It is generally used in the form of its salts such as sulphite, bisulphate and metabisulphite.
            Potassium metabisulphite (K2O 2So2 (or) K2S2O5) is commonly used as a stable source of So2. Being a solid, it is easier to use than liquid (or) gaseous So2.It is fairly stable in neutral (or) alkaline media but decomposed by weak acids like carbonic, citric, tartaric acid and malic acids. When added to fruit juice (or) squash it reacts with the acid in the juice forming the potassium salt and So2, which is liberated and forms sulphurous acid with the water of the juice. The reactions involved are as follows        

Potassium                                          Potassium     Sulphur
meta bisulphate  + Citric acid             Citrate       +  dioxide   + H­2O

                  SO2  +  H2O                H2SO3 (Sulphurous acid)
             SO2 has a better preservative action than sodium benzoate against bacteria and moulds. It also retards the development of yeasts in juice, but cannot arrest their multiplication, once their number has reached a high value.
            It is well known that fruit juices with high acidity do not undergo fermentation readily. The preservative action of the fruit acid its due to is hydrogen ion concentration. The pH for the growth of moulds ranges from 1.5 to 8.5, that of yeasts from 2.5-8.0, and of bacteria from 4.0 to 7.5.As fruit beverage like citrus squashes and cordials have generally a pH of 2.5 to 3.5, the growth of moulds and yeasts in them cannot be prevented by acidity alone. Bacteria, however, cannot grow. The pH is therefore, of great importance in the preservation of food product and by regulating it, one or more kinds of microorganisms in the beverage can be eliminated.
            The concentration of So2 required to prevent the growth of mirgroorganism at different pH levels are as under.

            The toxicity of So2 increases at high temperature. Hence its effectiveness depends on the acidity, pH, temperature and substances present in fruit juice.
            According to FPO, the maximum amount of So2 allowed in fruit juice is 700 ppm, in squash, crush and cordial 350 ppm and in RTS and nectar 100 ppm. The advantages of using So2 are  a) It has a better preserving action than sodium benzoate against bacterial fermentation b) it helps to retain the colour of the beverage for a longer time than sodium benzoate ( c) being a gas, it helps in preserving the surface layer of juices also (d) being highly soluble in juices and squashes, it ensures better mixing and hence their preservation and (e) any excess of So2 present can be removed either by heating the juice to about 71oC or by passing air through it or by subjecting the juice to vacuum. This causes some loss of the flavouring materials due to volatilization, which can be compensated by adding flavours.
Disadvantages (or) limitations
a.   It cannot be used in the case of some naturally coloured juices like those of jamun, pomegranate, strawberry, coloured grapes, plum etc. on account of its bleaching action.
b.   It cannot also be used for juices which are to be packed in tin containers because it not only corrodes the tin causing pinholes, but also forms H2S which has a disagreeable smell and reacts with the iron of the tin container to form a black compound, both of which are highly undesirable and
c.   So2 gives a slight taste and colour to freshly prepared beverages but these are not serious defects if the beverage is diluted before drinking.
II. Benzoic acid
            It is only partially soluble in H2O hence its salt, sodium benzoate is used. One part of sodium benzoate is soluble in 1.8 parts of water at ordinary temperature, whereas only 0.34 parts of benzoic acid is soluble in 100 parts of water. Sodium benzoate is thus nearly 170 times as soluble as benzoic acid, pure sodium benzoate is tasteless and odourless.
            The antibacterial action of benzoic acid is increased in the presence of Co2 and acid e.g. Bacillus subtilis cannot survive in benzoic acid solution in the presence of Co2. Benzoic acid is more effective against yeasts than against moulds. It does not stop lactic acid and acetic acid fermentation.
            The quantity of benzoic acid required depends on the nature of the product to be preserved, particularly its acidity. In case of juices having a pH of 3.5-4.0, which is the range of a majority of fruit juices, addition of 0.06 to 0.10% of sodium benzoate has been found to be sufficient. In case of less acid juices such as grape juice atleast 0.3% is necessary. The action of benzoic acid is reduced considerably at pH 5.0. Sodium benzoate is excess of 0.1% may produce a disagreeable burning taste. According to FPO its permitted level in RTS and nectar is 100 ppm and in squash, crush and cordial 600 ppm.
            In the long run benzoic acid may darken the product. It is, therefore, mostly used in coloured products of tomato, jamun, pomegranate, plum, watermelon, strawberry, coloured grapes etc.
Preservation by fermentation
            Decomposition of carbohydrates of microorganisms or enzymes is called fermentation. This is one of the oldest methods of preservation. By this method, foods are preserved by the alcohol or organic acid formed by microbial action. The keeping quality of alcoholic beverages, vinegars, and fermented pickles depends upon the presence of alcohol, acetic acid and lactic acid respectively. Wines, beers, vinegar, fermented drinks, fermented pickles etc., are prepared by these processes.
            Fourteen per cent alcohol acts as a preservative in wines because yeasts, etc., cannot grow at that concentration. About 2% acetic acid prevents spoilage in many products.

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UNIT LAYOUT-SELECTION OF SITE AND PRECAUTIONS FOR HYGIENIC CONDITIONS OF THE UNIT
Availability of raw materials

Raw material is of primary importance. It should be of very high quality. The price of the raw material is one of the main factors which affect the cost of the finished products. In India, the price of fruits and vegetables is quite high in the beginning of the season but there is a glut when plenty o0f raw material of excellent quality can be purchased at low cost.
Site and building
            The site of the plant dealing with fruits and vegetables should be near the growing area to ensure the ready availability of freshly picked raw materials and to minimize the time taken for its transport.
The site should have adequate water supply and enough space should be available so that there is no congestion and there is scope for further expansion of the plant. Sites having factories nearby which emits fumes that contaminate the air are not suitable.
After selecting the site the question of the type of building is to be considered. Existing old buildings are not suitable. The building should be designed for Indian conditions. Single- storied structures based o0n the requirement of working space, cost of the land, etc., are preferable as all equipments heavy machinery can be erected without difficulty and can be shifted easily whenever necessary. Ventilation and lighting are also better in single –storied buildings. Generally fruit and vegetable processing units are single-storied. The division of space should be done according to the steps of the process.
Receiving and storage section
            The area will depend on the nature of the raw materials. The receiving area should be as near to rail and road as possible specially where perishable products are concerned.
Preparation section
            The preparation section of fruit and vegetable processing plant requires a greater area. It should be well sanitated so that the risk of spoilage is reduced. The section should be fitted with water and steam lines such that the spreading of hoses while washing is avoided. As far as possible floors should be (a) resistant to chemicals, (b) resistant to wear (c) slip-proof, and d) have proper slope with clean and well-placed drains. The area can also be subdivided into different compartments for washing, peeling or shelling, extraction of juice, etc.
Filling, exhausting, sealing and processing section: care should be taken to control the humidity in this section where process like exhausting and sterilizing operations are mainly carried out. The floor should be quite sturdy to withstand heavy wear and tear.
Finishing section
This section where incubation, lacquering, labeling and packing are done should be scrupulously clean, cool and dry with good ventilation.
Laboratory
            Although a laboratory is expensive to set-up it is a very important unit in a fruit and vegetable processing plant. Its functions are: (a) examination of raw materials (b) control of processes (c) quality control of finished products (d) introduction of new processes and better products and (e) development of new techniques.
Apart from these sections, there should be suitable arrangement for storing, keeping machinery and other equipment and disposal of waste.
 Water supply
Water plays an important role in the food industry. It is used in substantial quantities for (a) cleaning of equipment, floors, walls, etc., (b) washing and preparation of raw materials, (c) preparation of brine, syrups, etc., (d) blanching, (e) cooling of processed cans, and (f) steam generation, etc.
            The water should be free from contamination. If necessary, it should be chlorinated.
Disposal of waste
            A large quantity of waste is produced by a cannery, containing a high percentage of solid matter, such as skins, peels and colloidal starchy material. Hence the cannery should be situated at such a place where waste could also be profitably utilized to make by-products.
Transport facilities
It is essential that the cannery should be situated near a road which connects it important towns in that area.
SANITARY REQUIREMENTS OF A FACTORY OF FRUIT PRODUCTS

1. The Premises – adequately lighted, ventilated & cleaned by white washing/color washing or oil painting.
2. Windows & all openings shall be well screened with wire-mesh & the doors fitted with automatic closing springs, roof shall be permanent, floor cemented.
3. The equipments and the factory l not be used for manufacture of repugnant products like fish, meat, eggs etc.
4. The premises – located in a sanitary place with open surroundings, preferably in                industrial area/estates. Communicated not directly with residence.
5. Adequate arrangements for cleaning equipments, machinery, containers tables and raw materials shall be provided. Copper, brass or iron equipments, containers or vessels are not permitted.
6.  The water used shall be potable.
7.  Adequate drainage system and provisions for disposal of refuse shall be made.
8.  Sufficient number of latrine & urinals shall be provided for workers.
9.  Wherever cooking is done on open fire, proper outlets for smoke/steam etc. like chimney, exhaust fan etc. shall be provided.
10.  The workers engaged in the factory shall be healthy and shall be medically examined, inoculated and vaccinated whenever required.
11.  The workers shall be provided with aprons, head-wears gloves etc. and shall be personally neat and tidy.

            Satisfactory hygienic conditions are also maintained during processing, in order to protect the product from bacterial contamination. For the routine bacteriological control of the plant or factory, counts on utensils, equipment, working surfaces, walls and floors are regularly carried out and the results tabulated or recorded on charts to give an immediate indication of any change. The counts are used as a check on the sanitary conditions of the plant. If the sanitary conditions of manufacture are to be passed as being “good”, the general bacterial counts must be low. In addition, periodic inspection of the plant is made by a trained inspector to make sure that adequate hygiene standards are maintained.

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PRESERVATION THROUGH CANNING, BOTTLING, FREEZING, DEHYDRATION, DRYING, ULTRAVIOLET AND IONIZING RADIATIONS

PRESERVATION THROUGH CANNING

The process of sealing food stuffs hermetically in containers and sterilizing them by heat for long storage is known as canning.
            In 1804, Appert in France invented a process of sealing foods hermetically in containers and sterilizing them by heat. In honour of the inventor, canning is also known as appertizing. Saddington in England was the first to describe a method of canning of foods in 1807. In 1810, Peter Durand, another Englishman, obtained the first British Patent on canning of foods in tin containers. In 1817, William Underwood introduced canning of fruits on a commercial scale in U.S.A.
            Fruits and vegetables are canned in the season when the raw material is available in plenty. The canned products are sold in the off-season and give better returns to the grower.
Principles and Process of Canning  
Principle
Destruction of spoilage organisms within the sealed container by means of heat.

(1) Selection of fruits and vegetables

1. Fruits and vegetables should be absolutely fresh.
2. Fruits should be ripe, but firm, and uniformly mature. Over-ripe fruits should be rejected
3. because they are infected with microorganisms and give a poor quality product. Unripe
4. fruits should be rejected because they generally shrivel and toughen on canning.
5. All vegetables except tomatoes should be tender.
6. Tomatoes should be firm, fully ripe and of deep red colour.
7. Fruits and vegetables should be free from dirt.
8. They should be free from blemishes, insect damage or mechanical injury.

(2) Grading
            The selected fruits and vegetables are graded according to size and colour to obtain uniform quality. This is done by hand or by machines such as screw grader and roller grader. Fruits like berries, plums and cherries are graded whole, while peaches, pears, apricots, mangoes, pineapple, etc., are generally graded after cutting into pieces or slices.

(3) Washing
            It is important to remove pesticide spray residue and dust from fruits and vegetables. One gram of soil contains 1012 spores of microorganisms. Therefore, removal of microorganisms by washing with water is essential. Fruits and vegetables can be washed in different ways. Root crops that loosen in soil are washed by soaking in water containing 25 to 50 ppm chlorine (as detergent). Other methods of washing are spray washing, steam washing, etc. 
(4) Peeling
            The objective of peeling is to remove the outer layer. Peeling may be done in various ways.
Hand peeling
It is done mostly in case of fruits of irregular shape, e.g., mango and papaya, where mechanical peeling is not possible.
Steam peeling
Free-stone and clingstone peaches are steam peeled in different ways. The former are cut and steam washed. Potatoes and tomatoes are peeled by steam or boiling water.
Mechanical peeling
This is done in case of apples, peaches, pineapples and cherries and also for root vegetables like carrots, turnips and potatoes.
Lye peeling
Fruits like peaches, apricots, sweet oranges, mandarin oranges and vegetables like carrots and sweet potatoes are peeled by dipping them in 1 to 2 per cent boiling caustic soda solution (lye) for 30 seconds to 2 minutes depending on their nature and maturity. Hot lye loosens the skin from the flesh by dissolving the pectin. The peel is then removed easily by hand. Any trace of alkali is removed by washing the fruit or vegetable thoroughly in running cold water or dipping it for a few seconds in 0.5 per cent citric acid solution. This is a quick method where by cost and wastage in peeling is reduced.
Flame peeling
It is used only for garlic and onion which have a papery outer covering. This is just burnt off.  Vegetables like peas are shelled, carrots are scarped, and beans are snipped or trimmed.
(5)  Cutting
            Pieces of the size required for canning are cut. Seed, stone and core are removed. Some fruits like plum from which the seeds cannot be taken out easily are canned whole.
(6) Blanching
            It is also known as scalding, parboiling or precooking. It is usually done in case of vegetables by exposing them to boiling water or steam for 2 to 5 minutes, followed by cooling. The extent of blanching varies with the food. Generally fruits are not blanched. This brief heat treatment accomplishes the following:

1. Inactivates most of the plant enzymes which cause toughness, discolouration

(polyphenol oxidase), mustiness, off-flavour (peroxidase), softening and loss of nutritive value.

1. Reduces the area of leafy vegetables such as spinach by shrinkage or wilting,

making their packing easier.

1. Removes tissue gases which reduce sulphides.
2. Reduces the number of microorganisms by as much as 99%.
3. Enhances the green colour of vegetables such as peas, broccoli and spinach.
4. Removes saponin in peas.
5. Removes undesirable acids and astringent taste of the peel, and thus improves

flavour.

1. Removes the skin of vegetable such as beetroot and tomatoes which helps in their peeling.   

Disadvantages

1. Water-soluble materials like sugar and anthocyanin pigments are leached by boiling water.
2. Fruits lose their colour, flavour and sugar.

(7) Cooling            
            After blanching, the vegetables are dipped in cold water for better handling and keeping them in good condition.
(8) Filling
            Before filling, cans are washed with hot water and sterilized but in developing countries these are subjected to a jet of steam to remove dust and foreign material. Automatic, large can-filling machines are used in advanced countries but choice grades of fruits are normally filled by hand to prevent bruising. In India, hand filling is the common practice. After filling, covering with syrup or brine is done and this process is called syruping or brining.
          A 1-b butter size can should hold 230 285 g of fruit slices and a A 2 ½  size can 510 to 565 g.
         The blanched vegetables are packed in sterilized cans which should hold the drained weight of vegetables as specified below:
            1 lb butter size can                –           269-283 g    
            A 2 ½ size can                       –           538-566 g
            Pint size glass jar                  –           283-311 g
(i) Syruping
            A solution of sugar in water is called a syrup. Normally sucrose syrup is used in canning. Syrup is added to improve the flavour and to serve as a heat transfer medium for facilitating processing. Syruping is done only for fruits.
            Strained, hot syrup of concentration 20 to 55o Brix is poured on the fruit. Fruits rich in acid require a more concentrated syrup than less acid ones. The syrup should be filled at about 79 to 82oC, leaving a head space of 0.3 to 0.5 cm. Sometimes citric acid and ascorbic acid are also mixed with the syrup to improve flavour and nutritional value, respectively.
(ii) Brining
            A solution of salt in water is called brine. The objective of brining is similar to that of syruping. Only vegetables are brined. Common salt of good quality free from iron should be used. Hot brine of 1 to 3 per cent concentration is used for covering vegetables and is filled at 79 to 82oC, leaving a head space of 0.3 to 0.5 cm. The brine should be filtered through a thick cloth before filling.
            After syruping or brining the cans are loosely covered with lids and exhausted. Lidding has certain disadvantages such as spilling of the contents and toppling of the lids. Hence lidding has now been modernized by ‘clinching’ process in which the lid is partially seamed. The lid remains sufficiently loose to permit the escape of dissolved as well as free air from the can and also the vapour formed during the exhausting process.
(9) Exhausting
            The process of removal of air from cans is known as exhausting. After filling and lidding or clinching, exhausting is essential. The major advantages of exhausting are as under:
a)     Corrosion of the tinplate and pinholing during storage is avoided.
b)     Minimizes discolouration by preventing oxidation.
c)      Helps in better retention of vitamins particularly vitamin C.

)     Prevents bulging of cans when stored in a hot climate or at high altitude.        
e)     Reduces chemical reaction between the container and the contents.
f)        Prevents development of excessive pressure and strain during sterilization.

Containers are exhausted either by heating or mechanically. The heat treatment method is generally used. The cans are passed through a tank of hot water at 82 to 87oC or move on a belt through a covered steam box. In the water exhaust box, the cans are placed in such a manner that the level of water is 4-5 cm below their tops. The exhaust box is heated till the temperature of water reaches 82 to 100oC and the centre of the can shows a temperature of about 79oC. The time of exhausting varies from 6 to 10 minutes, depending on the nature of the product. In the case of glass jars or bottles, vacuum closing machines are generally used. The bottles or jars are placed in a closed chamber in which a high vacuum is maintained.
      It is preferable to exhaust the cans at a lower temperature for a longer period to ensure uniform heating of the contents without softening them into pulp. Exhausting at high temperature should be avoided because the higher the temperature, the more is the volume of water vapour formed, and consequently the greater the vacuum produced in the can.
(10) Sealing
            Immediately after exhausting the cans are sealed airtight by means of a can sealer. In case of glass jars a rubber ring should be placed between the mouth of the jar and the lid, so that it can be sealed airtight. During sealing the temperature should not fall below 74oC.
(11) Processing
            Heating of foods for preserving is known as processing, however, in canning technology processing means heating or cooling of canned foods to inactivate bacteria. Many bacterial spores can be killed by either high or every low temperature. Such drastic treatment, however affects the quality of food. Processing time and temperature should be adequate to eliminate all bacterial growth. Moreover, over-cooking should be avoided as it spoils the flavour as well as the appearance of the product.      
            Almost all fruits and acid vegetables can be processed satisfactorily at a temperature of 100oC, i.e., in boiling water. The presence of acid retards the growth of bacteria and their spores. Further, they do not thrive in heavy sugar syrup which is normally used for canning of fruits. Vegetables (except the more acid ones like tomato and rhubarb) which are non-acid in nature, have a hard texture, and proximity to soil which many infect them with spore-bearing organisms processed at higher temperatures of 115 to 121oC.
            The sourness of fruits and vegetables is due to their acid content (measured in pH) which has a great influence upon the destruction of microorganisms. The lower the pH the greater is the ease with which a product can be processed or sterilized. Fruits and vegetables can be classified into the following four groups according to their pH value.

           
            Bacterial spores can be more easily destroyed at pH 3.0 (fruits) than at pH 5.0 to 6.0 (vegetables, except tomato and rhubarb). Bacterial spores do not grow or germinate below pH 4.5. Thus, a canned product having pH less than 4.5 can be processed in boiling water but a product with pH above 4.5 requires processing at 115 to 121oC under a pressure of 0.70 to 1.05 kg/cm2 (10 to 15 lb/sq inch). It is essential that the centre of the can should attain these high temperatures.
            The temperature and time of processing vary with the size of the can and the nature of the food: the larger the can, the greater is the processing time. Fruits and acid vegetables are generally processed in open type cooker, continuous non-agitating cookers, while vegetables (non-acid) are processed under steam pressure in closed retorts known as automatic pressure cookers and continuous agitating cookers. In India, small vertical stationary retorts (frontispiece) are generally used for canned vegetable processing. The sealed cans are placed in the cookers, keeping the level of water 2.5 to 5.0 cm above the top of the cans. The cover of the cooker is then screwed down tightly and the cooker heated to the desired temperature. The period of sterilization (process) should be counted from the time the water starts boiling. After heating for the required period the cooker is removed from the fire and the petcock is opened. When the pressure comes down to zero the cover is removed and the cans are taken out.   
(12) Cooling          
             After processing, the cans are cooled rapidly to about 39oC to stop the cooking process and to prevent stack-burning. Cooling is done by the following methods.
(i)   Dipping or immersing the hot cans in tanks containing cold water.
(ii)  Letting cold water into the pressure cooker specially in case of vegetables.
(iii) Spraying cans with jets of cold water; and
(iv) Exposing the cans to air.
  Generally the first method, i.e. dipping the cans in cold water, is used. If canned products are not cooled immediately after processing, peaches and pears becomes dark in colour, tomatoes turn brownish and bitter in taste, peas become pulpy with cooked taste and many vegetables develop flat sour (become sour).
(13) Storage
            After labelling the cans, they should be packed in strong wooden cases or corrugated cardboard cartons and stored in a cool and dry place. The outer surface of the cans should be dry as even small traces of moisture sometimes induce rusting. Storage of cans at high temperature should be avoided, as it shortens the shelf-life of the product and often leads to the formation of hydrogen swell.
The marketable life of canned products varies according to the type of raw materials used. Canned peach, grapefruit, pineapple, beans, spinach, pea, celery, etc. can be stored for about two years, while pear, apricot, carrot, beetroot, tomato, etc. can be stored for a comparatively long period.
PRESERVATION BY BOTTLING
Bottles have proved to be very good containers for home preservation of fruits. Although their initial cost is high, they can be used several times and last for many years if carefully handled.The fruits look attractive through glass and do not develop metallic flavour. Bottling does not need a sealing machine.
There are many types of glass containers of different shapes and sizes and with various types of hermetic seals. The products remain in a very hygienic condition and do not come into contact with rubber or metal.
Filling and syruping
The bottles are thoroughly washed and sterilized. The fruit slices are filled leaving about 3cm space at the top of the Jar or bottle. The sugar syrup recommended for different fruits is filled boiling hot leaving ahead space of 1-1.5cm.
Exhausting and sterilization

Separate exhausting of bottles is not required and it is done simultaneously with sterilization by putting a pad of cloth under the bottles. The bottles should not be abruptly immersed in hot water, otherwise they may break because of sudden rise in temperature. The temperature of the water should about the same as that of the same as that of the contents and should be raised gradually and the bottles kept i9n the boiling water for the required time. At the start of sterilization the lids are left loose and the level of boiling water should come up to the neck of the bottle, but when sterilization is over the mouths of bottles and jars should be immediately closed or corked tightly.
Cooling and storage
These are done as for canning of fruits and vegetables.
PRESERVATION BY FREEZING
At temperature below the freezing point of H2O, growth of microorganisms and enzyme activity are reduced to minimum. Most perishable foods can be preserved for several months. Fruits, vegetables, juices and fleshy foods (meat poultry fish and sea foods) can be preserved in this method.
Cold storage we generally means storage at temperature above freezing, and this covers a range of about 16oC (60oF) down to –2.2 oC (28oF).  Commercial and household refrigerators are usually run at 4.4o – 7.2 oC (40-45 oF).  While pure water will freeze at 0oC (32 oF)), most foods will not begin to freeze until about –2.2 oC) (28oF) or lower is reached.
            Frozen storage (Freezing) as the name implies refers to storage at temperatures where the food is maintained in frozen condition. Good frozen storage generally means – 18oC (0 oF) or below.
            Refrigerated or cold storage generally will preserve perishable foods for days or weeks depending upon the food. Frozen storage will preserve perishable foods for months or even years. Further distinctions between refrigeration and freezing temperatures are related to microorganisms activity. Most food spoilage microorganisms grow rapidly at temperatures above 10oC (50oF) .Some food poisoning organisms grow slowly down to 3.3oC (38 oF) psychrotropic organisms will grow slowly within the range of 4.4 oC to – 9.4 oC (40 oF to 15 oF), provided the food is not solidly frozen. These will not produce food poisoning or disease but even below – 3.9oC (25 oF) will cause the food to deteriorate. Below – 9.4oC (15 oF) there is no significant growth of microorganisms in food; instead there is a gradual decrease in the numbers of living organisms. But the destruction of microorganisms by cold is not complete when the food is thawed there can be rapid microorganisms multiplication and spoilage.
Characteristics of food systems being frozen
            It is a basic property of aqueous solutions that increasing their concentrations of dissolved solids will lower their freezing points. Thus the more salt, sugar, minerals, or proteins in a solution the lower the freezing point and the longer it will take to freeze when put into a freezing chamber. If water and juice are placed in a freezer the water will freeze first. Further, unless the temperature is considerably below the freezing point of pure water the juice will never freeze completely but rather will become icy and slushy. What really is happening here is that the water component of the juice freezes first and leaves the dissolved solids in a more concentrated solution which requires a still lower temperature to freeze it.
            Since different foods have quite different compositions with respect to their levels of water and the kinds and amounts of solids dissolved in the water, it is to be expected that these will have different freezing points and under a given freezing condition will require different times to reach a solidly frozen state.
Methods of freezing
There are various methods of freezing
1. Sharp Freezing (Slow freezing)
            This technique, first used in 1861, involves freezing by circulation of air, either naturally or with the aid of fans. The temperature may vary from –15 to –29oC and freezing may take from 3 to 72 hours. The ice crystals formed one large and rupture the cells. The thawed tissue cannot regain its original water content. The first products to be sharp frozen were meat and butter. Now-a-days freezer rooms are maintained at –23 to –29oC or even lower, in contrast to the earlier temperature of –18oC.
2. Quick freezing 
            In this process the food attains the temperature of maximum ice crystal formation (0 to – 4oC) in 30 min or less. Such a speed results in formation of very small ice crystals and hence minimum disturbance of cell structure. Most foods are quick frozen by one of the following three methods:
a) By direct immersion
            Since liquids are good heat conductors food can be frozen rapidly by direct immersion in a liquid such as brine or sugar solution at low temperature. Berries in sugar solution packed fruit juices and concentrates are frozen in this manner. The refrigeration medium must be edible and capable of remaining unfrozen at –18oC and slightly below. Direct immersion equipments such as ottenson Brine freezer, Zarotschenzeff ‘Fog’ freezer, T.V.A. freezer, Bartlett freezer etc. of commercial importance earlier are not used today.
Advantages 

1. There is perfect contact between the refrigerating medium and the product, hence the rate of heat transfer is very high.
2. Fruits are frozen with a coating of syrup which preserves the colour and flavor

during storage.

1. The frozen product is not a solid block because each piece is separate.

Disadvantages

1. Brine is a good refrigerating medium but it cannot be used for fruits.
2. It is difficult to make a syrup that will not become viscous at low temperature.
3. The refrigeration temperature must be carefully controlled, as at high temperature the medium will enter the product by osmosis and at low temperature the medium may freeze solid.
4. It is very difficult to maintain the medium at a definite concentration and also to keep it free from dirt and contamination. 

b) By indirect contact with refrigerant
            Indirect freeing may be defined as freezing by contact of the product with a metal surface which is itself cooled by freezing brine or other refrigerating media. This is an old method of freezing in which the food or package is kept in contact with the passage through the refrigerant at –18 to -46oC flows. Knowles Automatic Package feezer, Patterson continuous plate freezer, FMC continuous can freezer and Birds eye freezers are based on this principle.
c) By air blast
            In this method, refrigerated air at –18 to –34oC is blown across the material to be frozen. The advantages claimed for quick freezing over slow freezing (sharp freezing) are  (1) smaller (size) ice crystals are formed, hence there is less mechanical destruction of intact cells of the food (2) period for ice formation is shorter, therefore, there is less time for diffusion of soluble material and for separation of ice (3) more rapid preservation of microbial growth and (4) more rapid slowing down of enzyme action.
3) Cryogenic freezing
            Although most foods retain their quality when quick frozen by the above methods, a few require ultrafast freezing. Such materials are subjected to cryogenic freezing which is defined as freezing at very low temperature (below –60oC). The refrigerant used at present in cryogenic freeing are liquid nitrogen and liquid CO2. In the former case, freezing may be achieved by immersion in the liquid, spraying of liquid or circulation of its vapour over the product to be frozen.
4. Dehydro-freezing
            This is a process where freezing is proceded by partial dehydration. In case of some fruits and vegetables about 50% of the moisture is removed by dehydration prior to freezing. This has been found to improve the quality of the food. Dehydration does not cause deterioration and dehydro frozen foods are relatively more stable.
5. Freeze drying
            In this process food is first frozen at –18oC on trays in the lower chamber of a freeze drier and the frozen material dried (initially at 30oC for 24 hrs and then at 20oC). Under high vacuum (0.1 mm Hg) in the upper chamber. Direct sublimation of the ice takes place without passing through the intermediate liquid stage. The product is highly hygroscopic, excellent in taste and flavour and can be reconstituted readily. Mango pulp, orange juice concentrate, passion fruit juice and guava pulp are dehyderated by this method.
Changes during freezing and storage of frozen products
            Quick freezing rapidly slow down chemical and enzymatic reactions in foods and stops microbial growth. A similar effect is produced by sharp freezing, but less rapidly. The physical effects of freezing are of great importance. This is an expansion in volume of the frozen food and ice crystals form and grow in size. These crystals are larger in slow freezing than in quick freezing and more ice accumulates between tissue cells and may crash the cells. Water is drawn from the cells to form ice. It is claimed that ice crystals rapture fruit and vegetable tissue cells and even microorganism. The increased concentration of solutes in the cells hastens their salting out, dehydration and denaturation of proteins and causes irreversible changes in colloidal systems, such as the syneresis of hydrophilic colloids. Further, freezing is considered to be responsible for killing microorganisms. The vegetative cells of yeasts and moulds and many gram negative bacteria are susceptible, while gram – positive bacteria including staphyloeocci and enterococci are moderately resistant, while spores bacilli and clostridia are insensitive to freezing.

During storage of food in the frozen condition, chemical and enzymatic reactions proceed slowly. Unfrozen concentrated solution of sugars, salts etc. May ooze out from fruits or concentrates during storage as a viscous material called ‘metacryotic liquid’. Fluctuation in storage temperature results in an increase in the size of ice crystals resulting in physical damage to the food. Desiccation of the food at its surface is likely to take place during storage. When ice crystals evaporate from the surface of fruit, “freezer burn” is produced which usually appears as dry, grainy and brownish spots where the chemical changes mentioned above takes

place and the tissues become dry and tough. There is slow but continuous decrease in the number of viable microorganisms on storage.
Freezing – 18 to –40oC
Freezing process of fruits, vegetables and juices
Suitable vegetables: Beans, cauliflower, peas, carrot etc.
Suitable fruits:  Pineapple slices, mango slices or pulp, guava slices and orange. segments etc.
I. Beans
Beans (mature) → Removal of strings (fibre) → Cutting into 2 cm pieces → Blanching for 5 min (Direct immersion, no cloth bag)  Cooling in water → Packing in polythene bags → Sealing →Arranging in carotene → Freezing by plate frozen (takes about 2 hrs to reach -1 to -5oC when product is considered to be frozen) → Storage at – 18oC.
II. Carrot
            Carrot → Washing → Peeling of skin → Cutting into 2 cm pieces → Blanching for 3 min (no cloth bag) → Cooling → Packing in polythene bags → Sealing → Arranging in cartons → Freezing at –1 to –5oC → Storage → 18oC. 
III. Peas
Peas → Washing → Removal of shell → Washing → Blanching for 4 min → Cooling → Preliminary grading by density gradient using 10% brine (Flaters → immature peas, sinkers → mature peas) → Further grading of mature peas, using 9%, 13% and 15% brine → Packing in polythene bags. Floaters 9% – A grade,  13% – B grade, 15% – C grade, → Sealing → Arranging in cartons → Freezing at – 1oC to – 5oC → Storage at – 18oC.
IV. Cauliflower
Cauliflower (mature) → Cutting into bits – Blanching for 2 min → Cooling → Dipping in 0.05% KMS solution for 5 min → Draining → Packing in polythene bags → Sealing → Arranging in cartons → Freezing at –1 to –5oC → Storage at –18oC.
V. Guava
Guava → Washing – Placing in 2% boiling lye till skin becomes black → Removing and washing with H2O → Dipping in 0.5% citric acid solution → Cutting into 4 pieces → Scooping out seeds → Packing pieces in polythene bags and covering with 25% sugar syrup containing 100 mg ascorbic acid → Sealing → Arranging in cartons → Freezing at –1 to –5oC → storage at –18oC.
VI. Orange
Orange → Peeling → Separating segments → Treatment with hot 1% lye →Washing with water → Dipping in 1% citric acid solution → Removing seeds → Packing in polythene bags and covering with 25% sugar syrup containing 100 mg of ascorbic acid → Sealing → Arranging in cartons → Freezing at –1 to –5oC – Storage at – 18oC.
PRESERVATION BY DEHYDRATION /DRYING
The practice of drying of food stuffs, specially fruits and vegetables, for preserving them is very old. The term ‘drying’ and ‘dehydration’ means the removal of water. The former term is generally used for drying under the influence of non-conventional energy sources like sun and wind. If fruits (or) vegetables are to be sun dried, they (or) their pieces should be evenly spread in single layer (on) trays or boards and exposed to the sun. In sun drying there is no possibility of temperature and humidity control.  The hottest days in summer are, therefore, chosen so that the foods dry very fast, thus preventing them from getting spoiled due to souring. Souring (or) turning acidic is usually due to growth of microorganisms which convert the carbohydrates in the food to acid. Quick removal of moisture prevents the growth of the microorganisms.
            Dehydration means the process of removal of moisture by the application of artificial heat under controlled conditions of temperature, humidity and air flow.  In this process a single layer of fruits (or) vegetables, whole or cut into pieces (or) slices are spread on trays which are placed inside the dehydrator. The initial temperature of the dehydrator is usually 43oC which is gradually increased to 60-66oC in the case of vegetables and 50-71 oC for fruits.
Advantages of dried / dehydrated foods

1. Dried foods are in more concentrated form than foods preserved in other ways. They are less costly to produce than canned or preserved food, because of lower labour costs and because of no sugar is required.
2. Due to reduction in bulk of the product, it requires less storage space.
3. The weight of a product is reduced to 1/4th to 1/9th its original (or) fresh weight and thus the cost of its transport is reduced.

Sundrying
            Sundrying of fruits and vegetables is practiced widely in tropical and subtropical regions where there is plenty of sun shine and practically little or no rain during the drying season. Sundrying in direct (or) diffused sunlight (shade drying), one of the earliest method of food preservation, is still used for the production of dried fruits, and also for drying nuts. It was originally limited to fruits high in sugar content, which when harvested, would dry naturally without hazard of loss from fermentation and molding.
Process for drying of fruits
Fruits (mature and free from insects and disease→ Washing → Peeling / removal of outer skin → Preparation → Pretreatments → Spreading on flat wooden trays → Sulphuring → Drying → Sweating → Packaging in air tight tin containers (or) polythene bags → Storage (at ambient temperature).
Pretreatments
Lye peeling
Dipping the fruits (grapes and dates) in 0.5% to 2.5% boiling caustic soda solution for 0.5 to 2.0 minutes depending on their nature and maturity. Hot lye loosens the skin from the flesh by dissolving the pectin. The peel is then removed easily by hand. Any trace of alkali is removed by washing the fruit thoroughly in running cold water (or) dipping it for a few seconds in 0.5% citric acid solution.
Sulphuring
Sulphuring is done only for fruits and not vegetables. So2 fumes act as a disinfectant and prevent the oxidation and darkening of fruits on exposure and thus improves their colour. This phenomenon is generally seen in sliced fruits which darken due to oxidation of the colouring matter. Sulphur fumes also act as a preservative, check the growth of molds etc. and prevent cut fruit pieces from fermenting while drying in the sun. Vitamins in sulphured fruits are protected but not in unsulphured ones.
            The whole fruits, slices (or) pieces are exposed to the fumes of burning sulphur inside a closed chamber known as sulphur box for 30-60 min. or in small airtight rooms.
            Sulphur box is a closed airtight chamber of galvanized iron sheet. It is fitted in a wooden frame work having runways on both sides to hold the trays. For small scale sulphuring, a box of size of 90 x 60 x 90 cm which can hold 11 trays, each of 80 x 60 x 5 cm size is suitable. A box holding 10 trays will require burning of about 3 g of sulphur in one charge.
Sweating
Keeping dried products in boxes or bins to equalize moisture content.
Sundrying of fruits
1. Banana
Dried ripe banana is known as ‘banana fig’. The fruit is peeled, sliced lengthwise, sulphured and dried in the sun. Unripe bananas are peeled after blanching in boiling water and cut into discs for drying. The dried slices are either cooked or fried. They can also be converted into banana flour which can be used as such or in combination with cereal flours.
2.  Date
In the hard dried dates, sucrose sugar predominates, whereas in the soft dried dates, invert sugars predominates. Dates are picked in the dung stage, that is when the tip of the fruit has turned a translucent brown. They are spread on mats for 5 to 8 days for curing. This is rather expensive as several pickings have to be made as the date attain other proper stage of ripening. Scientists have found that dates could be picked 3 to 4 days before the “dung” stage and then dipped for ½ to 2 min in 0.5-2.5 % caustic soda solution before placing them for drying in order to get a good dried product.
3. Fig
The fruits are allowed to ripen on the tree and gathered when they drop. They are then spread thinly on the drying yard for 3 to 4 days for drying. After drying they are sorted and packed. Figs are treated with salt and lime (1 kg of each per 1000 litrs of water) to remove the hair from the skin and also to soften the flesh. They are then dried without sulphuring, till there is exudation of juice on pressing the dried fig between the fingers.
4. Grapes
Large quantities of seedless grapes known as kishmish grapes are imported into India from Afghanistan. Ripe bunches of grapes are hung inside dark rooms known as kishmish khanas till the berries acquire a greenish or light amber tint. These shade dried grapes are considered to be a far superior to the ordinary sundried (or) dehydrated grapes. The other important dried grape called ‘Monucca’ (or) Rasisin is prepared from the large seeded Haitha grapes which are lye dipped prior to the sun drying.
For efficient drying, grapes should have a high sugar content of 20 to 24 degree brix. From this point of view, some of the varieties of grapes are not suitable for drying. The higher sugar content grapes are dried without any sulphuring till there is no exudation of juice on pressing dried grape between the fingers. The yield and quality of the final dried product depend on the brix of the fresh grape taken for drying.
In California, the Sultanina (or) Thompson seedless varieties of grapes are dried. The grapes are sometimes dipped for 3-6 seconds in caustic soda and sodium bicarbonate, covering the surface of a solution with a thin layer of olive oil. This treatment removes only the wax and the bloom on the grapes without cracking the skin. The dried product has a glossy appearance. Lye dipped grapes are sometimes treated with sulphur fumes, for 3-5 hrs for bleaching them, because certain markets prefer such glossy product.
            In Australia, potassium carbonate solution with a layer of olive oil (or) sometimes grape seed oil itself, is used for dipping the grapes. The drying is carried out on wire net racks arranged inside a shed. In this way, the grapes are dried without direct exposure to the sun. Drying takes 10-20 days depending upon the variety of grape. The dried product is generally of high quality.
5. Jack fruit

Jack fruit bulbs of ripe fruit are sliced and the seeds removed. The slices are dried with (or) without sulphuring. The bulbs can also be made into a fine pulp, which can be dried in the form of sheets or slabs.
6. Mango
Unripe, green mangoes are peeled, sliced and dried in the sun. The dried product is used for the preparation of mango powder which is added as a relish in various food preparations. Ripe mangoes are taken and the juicy pulp squeezed by hand. The pulp is spread on Bamboo mats and a small quantity of sugar sprinkled over it. Whet the first layer has dried, another layer of pulp is spread over it for drying. This process is repeated until the dried slab is 1.2 to 2.5 cm thick. The dried product has a light yellow amber colour and possess a delicious taste.
Other fruits
Pomegranate seeds are dried, and the dried product known as anardana is sued as a savoury and acidulant like tamarind in cooking. Apple rings are threaded and  dried by hanging them out to dry in the sun.
            The cereals, pulses and oilseeds are usually sundried in most of the areas after harvesting from the crop. Sundried vegetables results poor quality in physical and chemical characteristics during storage.
Types of drier
Drier type                                                     Usual food type
I. Air convection driers     
1.         Kiln drier Pieces
2.         Cabinet, tray or pan drier Pieces, purees, liquids
3.         Tunnel drier Pieces
4.         Continuous conveyor belt drier Purees, liquids
5.         Belt trough drier Pieces
6.         Air lift drier  Pieces, granules
7.         Fluidized bed drier Small pieces, granules
8.         Spray drier                                                     Liquids, purees
II.         Drum (or) Roller drier
1.         Atmospheric driers Purees, liquids
2.         Vacuum driers Purees, liquids
III.        Vacuum driers
1.         Vacuum shelf  Pieces, purees, liquids
2.         Vacuum belt Purees, liquids
3.         Freeze driers                                                 Pieces, liquids
Methods of drying
I. Air convection driers
            All air convection driers have some sort of insulated enclosures, a means of circulating air through the enclosure and a means of heating this air. They also will have various means of product support, special devices for dried product collection, some will have air driers to lower drying air humidity.
            Movement of air generally will be controlled by fans, blowers and baffles. Air volume and velocity will affect drying rate, but its static pressure also is important since products being dried become very light and can be blown off trays or belts.
            The air may be heated by direct or indirect methods. In direct heating the air is in direct contact with flame (or) combustion gases. In indirect heating the air is in contact with a hot surface, such as being blown across pipes heated by steam, flame or electricity. The important point is that indirect heating leaves the air uncontaminated. On the other hand in direct heating the fuel is seldom completely oxidized to CO2 and water. Incomplete combustion leaves gases and traces of soot and this is picked up by the air and can be transferred to the food product. Direct heating of air also contributes small amounts of moisture to the air since moisture is a product of combustion but this is usually insignificant except with very hygroscopic foods. These disadvantages are balanced by the generally lower cost of direct heating of air compared to indirect heating, and both methods are widely used in food dehydration.
1. Kiln drier
            Kiln driers of early design were generally two storey constructions. A furnace or burner on the lower floor generated heat, and warm air would rise through a slotted floor to the upper story. Foods such as apple slices would be spread out on the slotted floor and turned over periodically. This kind of drier generally will not reduce moisture to below about ten per cent. It is still in use for apple slices.
2. Cabinet, Tray and Pan driers
            Food may be loaded on trays or pans in comparatively thin layers upto a few centimeters. Fresh air enters the cabinet is drawn by the fan through the heated coil and is then blown across the food trays to exhaust. In this case the air is being heated by the indirect method. Screens filter out any dust that may be in the air. The air passes across and between the trays in this design. The air is exhausted to the atmosphere after one pass rather than being recirculated within the system. The moisture laden air, after evaporating water from the food, would have to be dried before being recirculated, or else it would soon become saturated and further drying of the food would stop.
            Cabinet, tray and pan driers are usually for small scale operations. They are comparatively inexpensive and easy to set in terms of drying conditions. They may run upto 25 trays high, and will operate with air temperatures of about 93oC dry bulb and air velocities of about 2.5 to 5.0 M/5 across the trays. The commonly are used to dry fruit and vegetable pieces, and depending upon the food and the desired final moisture, drying time may be of the order or 10 of even 20 hr.
3. Tunnel and continuous belt drier
            For larger operations we elongate the cabinet, place the trays on carts. If drying time to the desired moisture is 10 hr then each wheeled cart of trays will take 10 hr to pass through the tunnel. When a dry cart emerges it makes room to load another wet crat into the opposite end of the tunnel. Such an operation becomes semi continuous.
            A main construction feature by which tunnel driers differ has to do with the direction of air flow relative to tray movement. The wet food carts move from left to right. The drying air moves across the trays from right to left. This is the counter flow or countercurrent principle. Its significance is that the air, when it is hottest and driest, contacts the nearly dry product, whereas the initial drying of entering carts gets cooler, moisture air that has cooled and picked upto moisture going through the tunnel. This means that the initial product temperature and moisture gradients will not be as great and the product is less likely to undergo case hardening or other surface shrinkage leaving wet centers. Further, lower final moistures can be reached since the driest product encounters the dried air. In contrast, there also are concurrent flow tunnels with the incoming hottest, driest and travelling in the same direction. In this case rapid initial drying air slow final drying can cause case hardening and internal splits and porosity as centers finally dry, which sometimes is desirable in special products.
            Just as carts of trays can be moved through a heated tunnel, so a continuous belt may be driven through a tunnel or oven enclosure. Then we have a continuous belt or conveyor drier and a great number of designs are possible.
4. Belt trough drier
            A special kind of air convection belt drier is the belt trough drier in which the belt forms a trough. The belt is usually of metal mesh and heated air is blown up through the mesh. The belt moves continuously, keeping the food pieces in the trough in constant motion to continuously expose new surface. This speeds drying and with air of about 135oC, vegetable pieces may be dried to 7-5% moisture in about 1 hr.
            But not all products may be dried this way since certain sizes and shapes do not readily tumble. Fragile apple wedges may break. Onion slices tend to separate and become entangled. Fruit pieces that exude sugar on drying tend to stick together clump with the tumbling motion. These are but a few additional factors that must be considered in selecting a drier for a particular food.
5. Air lift drier
            Several types of pneumatic conveyor driers go a step beyond tumbling to expose more surface area of food particles. These generally are used to finish dry materials that have been partially dried by other methods, usually to about 25% moisture, or at least sufficiently low so that the material becomes granular rather than having a tendency to clump and mat.
6. Fluidized bed drier
            Another type of pneumatic conveyor drier is the fluidized bed drier. In fluidized bed drying, heated air is blown up through the food particles with just enough force to suspend the particles in a gentle boiling motion. Semidry particles such as potato granules enter at the left and gradually migrate to the right, where they are discharged dry. Heated air is introduced through a porous plate that supports the bed of granules. The moist air is exhausted   at the top. The process is continuous and the length of time particles remain in the drier can be regulated by the depth of the bed and other means. This type of drying can be used to dehydrate grains, peas and other particulates.
7. Spray driers
            The most important kind of air convection drier is the spray drier. Spray driers turn out a greater tonnage of dehydrated food products than all other kinds of driers combined, and there are various types of spray driers designed for specific food products.
            Spray driers are limited to foods that can be atomized, such as liquids and low viscosity pastes or purees. Atomization into minute droplets results in drying in a matter of seconds with common inset air temperatures of about 200oC. Since evaporative cooling seldom permits particles to reach above about 80oC (180oC) and properly designed systems quickly remove the dried particles from heated zones, this method of dehydration can produce exceptimally high  quality with many highly heat sensitive materials, including milk, eggs and coffee.
            In typical spray drying we introduce the liquid food as a fine spray or mist into a tower or chamber along with heated air. As the small droplets make intimate contact with the heated air they flash off their moisture, become small particles and drop to the bottom of the tower from where they are removed. The heated air which has now become most is withdrawn from the tower by a blown or fan. The process is continuous in that liquid food continues to the pumped into the chamber and atomized, along with dry heated air to replace the moist air that is withdrawn, and the dried product is removed from the chamber as it descends. 
            Milk and coffee powder is usually dried in the spray drier. Thermoplastic materials / substances viz., fruit juices are spray dried in a specially developed BIRS spray drier.
II. Drum (or) Roller driers
            In drum (or) roller drying, liquid foods, purees pastes and mashes are applied in a thin layer onto the surface of a revolving heated drum. The drum generally is heated from within by steam. Drier may have a single drum or a pair of drums. The food may be applied between the nip where two drums come together, and then the clearance between the drums determines the thickness of the applied food layer, or the food can be applied to other areas of the drum. Food is applied continuously and the thin layer loses moisture. At a point on the drum or drums a scraper blade is positioned to peel the thin dried layer of food from the drums. The speed of the drum is so regulated that the layer of food will be dry when it reaches the scraper blade, which also is referred to as a doctor blade. The layer of food is dried in one revolution of the drum and is scrapped from the drum before that position of the drum returns to the point where more wet food is applied. Using steam under pressure in the drum, the temperature of the drum surface may be well above 100oC, and is often held at about 150oC. With a food layer thickness commonly less than 2 mm, drying can be completed in 1 min or less, depending on the food material. Other features of drum driers include hoods above drums to withdraw moisture vapor and conveyers in troughs to receive and move dried product.
            Typical products dried on drums include milk, potato mash, heat tolerant purees such as tomato paste, and animal feeds. But drum drying has some inherent limitations that restrict the kinds of foods to which it is applicable. To achieve rapid drying, drum surface temperature must be high, usually above 120oC. This gives products a more cooked flavour and colour than when they are dried at a lower temperature. Drying temperature can, of course, be lowered by constructing the drums within a vacuum chamber but this increases equipment and operating costs over atmospheric drum or spray drying.
            A second limitation is the difficulty of providing zoned temperature control needed to vary to drying temperature profile. This is particularly important with thermoplastic food materials. Whereas dried milk and dried potato are easily scraped from the hot drum in brittle sheet form, this is not possible with many dried fruits, juices and other products which tend to be sticky and semimolten when hot. Such products tend to crimp, roll up, and otherwise accumulate and stick to the doctor blade in a taffy like mass.
This condition can be substantially improved by a cold zone to make the tacky material brittle just prior to the doctor blade. But zone controlled chilling is not as easy to accomplish on a drum of limited diameter and therefore limited arc, as it would be in perhaps 6 m of length of a horizontal drying belt 45 m long. One means of chilling is by directing a stream of cool air onto a segment of the product on the drum prior to the doctor blade.
For relatively heat resistant food products, drum drying is one of the least expensive dehydration methods. Drum dried foods generally have a somewhat more cooked character than the same materials spray dried; thus drum dried milk is not up to beverage quality but is satisfactory as an ingredient in less deligately flavoured manufactured foods. More gentle vacuum drum drying or zone-controlled drum drying increases dehydration costs.
III. Vacuum driers
Vacuum dehydration methods are capable of producing the highest quality dried products, but costs of vacuum drying generally also are higher than other methods which do not employ vacuum. In vacuum drying, the temperature of the food and the rate of water removal are controlled by regulating the degree of vacuum and the intensity of heat input.  Heat transfer to the food is largely by conduction and radiation.
All vacuum drying systems have four essential elements. These include a vacuum chamber of heavy construction to withstand outside air pressures, that may exceed internal pressures by as much as 9800 kg/cm2; means to supply heat; a device for producing and maintaining the vacuum; and components to collect water vapour as it is evaporated from the food.
The vacuum chamber generally will contain shelves or other supports to hold the food and these shelves may be heated electrically or by circulating a heated fluid through them. The heated shelves are called platens. The platens convey heat to the food in contact with them by conduction, but where several platens are one above another they also radiate heat to the food on the platen below. In addition, special radiant heat sources such as infrared elements can be focussed onto the food to supplement the heat conducted from platen contact.
The device for producing and maintaining vacuum will be outside the vacuum chamber and may be a mechanical vacuum pump or a steam ejector. A steam ejector is a kind of aspiration in which high velocity steam jetting past an opening draws air and water vapour from the vacuum chamber by the same principle that makes an insect spray gun draw fluid from the can.
 The means of collecting water vapour may be a cold wall condenser. It may be inside to vacuum chamber or outside the chamber but most come ahead of the vacuum pump so as to prevent water vapour from entering and fouling the pump. When a steam ejector can condense water vapour as it is drawn along the air from the vacuum chamber and so a cold wall vapour condeser may not be needed except where a very high degree of efficiency is required.
Degree of vacuum
            Atmospheric pressure at sea level is approximately 15 psi, or sufficient pressure to support a 30 inch column of mercury. This is equivalent to 760 mm of Hg or 1 in Hg is approximately 25 mm. At 1 atm or 30 in., or 760 mm of Hg, pure water boils at 100oC. At 10 in or 250 mm of Hg pure water boils at 72oC.  At 2 in. or 50 mm of mercury pure water boils at 38oC. High vacuum dehydration operates at still lower pressures such as fractions of mm of Hg. Freeze drying generally will operate in the range of 23 mm down to about 0.1 mm of Hg.
            There are two kinds of vacuum drier.
1. Vacuum shelf driers  
Batch type
If liquids such as concentrated fruit juices are dried above about 55 mm Hg, the juice boils and splatters, but in the range of about 3 mm Hg, and below, the concentrated juice puffs as it loses water vapour. The dehydrated juice then retains the puffed spongy structure. Since temperature well below 40oC can be used, in addition to quick solubility there is minimum flavour change or other kinds of heat damage. A vacuum shelf drier is also suitable for the dehydration of food pieces. In this case, the rigidity of the solid food prevents major puffing, although there also is a tendency to minimize shrinkage.
2. Continuous vacuum belt drier
Continuous type drier
This drier is used commercially to dehyderate high quality citrus juice crystals, instant tea and other delicate liquid foods.
            The drier consists of a horizontal tank like chamber connected to a vacuum producing, moisture condensing system. The chamber is about 17 m long and 3.7 m in diameter. Within the chamber are mounted two revolving hollow drums. Around the drum is connected a stainless steel belt which moves in a counter clock wise direction. This drum on the right is heated with steam confined within it. This drum heats the belt passing over it by conduction. As the belt moves, it is further heated by infrared radiant elements. The drum to the left is cooled with cold H2O circulated within it and cools the belt passing over it. The liquid food in the form of a concentrate is pumped into a feed pan under the lower belt strand. An applicator roller dipping into the liquid continuously applies a thin coating of the food onto the lower surface of a moving belt. As the belt moves over the heating drum and past the radiant heaters, the food rapidly dries in the vacuum equivalent to about 2 mm Hg. When the food reaches the cooling drum, it is down to about 2% moisture. At the bottom of the cooling drum is a doctor blade which scrapes the cooled, embrittled product into the collection vessel. The belt scrapped free of product receives additional liquid food as it passes the applicator roller and the process repeats in continuous fashion.
            Products dried with this equipment have a slightly puffed structure. If designed, a greater degree of puffing can be achieved. This has been done in the case of milk by pumping nitrogen gas under pressure into the milk prior to drying. Some of the gas goes into solution in the milk. Upon entering the vacuum chamber this gas comes out of solution violently and further puffs the milk as it is being dried.
3.  Freeze drying
            Freeze drying can be used to dehydrate sensitive high value liquid foods such as coffee and juices, but it is especially suited to dry solid foods of high value such as straw berries, whole shrimp, chicken dice, mushroom slices and sometimes food pieces as large as steaks and chops. These types of foods, in addition to having delicate flavours and colors, have textural and appearance attributes which cannot be well preserved by any current drying method except freeze drying. Any conventional drying method that employs heat would cause considerable shrinkage distortion and loss of natural strawberry structure (texture), upon reconstitution such as dried strawberry would not have the natural colour, flavour or turgor and would be more like a strawberry preserve or jam. This can be largely prevented by drying from the solidly frozen state, so that in addition to low temperature, the frozen food has no chance to shrink or distort while giving up its moisture. 
            The principle behind freeze drying is that under certain conditions of low vapor pressure, water can evaporate from ice without the ice melting. When a material can exist as a solid, a liquid and a gas but goes directly from a solid to a gas without passing through the liquid phase. The material is said to sublime. Dry ice sublimes at atmospheric pressure and room temperature. Frozen water will sublime if the temperature is 0oC or below and the frozen H2O is placed in a vacuum chamber at a pressure of 4.7 mm (or) less. Under such conditions the H2O will remain frozen and water molecules will leave the ice block at a faster rate than water molecules from the surrounding atmosphere reenter the frozen block.
            Within the vacuum chamber heat is applied to the frozen food to speed sublimation and if the vacuum is maintained sufficiently high usually within a range of about 0.1 to 2 mm g and the heat is controlled just short of melting the ice, moisture vapour will sublime at a near maximum rate. Sublimation takes place from the surface of the ice, and so as it continues the ice front recedes towards the center of the food piece; i,e. the food dries from the surface inward. Finally, the last of the ice sublimed and the food is below 5% moisture. Since the frozen food remains rigid during sublimation, escaping H2O molecules leave voids behind them, resulting in porous sponge like dried structure. Thus freeze dried foods reconstitute rapidly but also must be protected from ready absorption of atmospheric moisture and O2 by proper packaging.
A heating plate is positioned above and below the food to increase heat transfer rate but an open space is left with expanded metal so as not to seal off escape of sublimed H2O molecules.  Nevertheless, as drying progresses and the ice front recedes, drying rate drops off for several reasons. Thus the porous dried layer ahead of the reducing ice layer acts as an effective insulator against further heat transfer and the porous layer slows down the rate of escape of H2O molecules subliming from the ice surface.
4. Foam mat drying
            The foam is deposited on a perforated tray or belt support as a uniform layer approximately 3 mm thick. Just before the perforated support enters the heated oven it is given a mild air blast from below. This forms small craters in the stiff foam which further expands foam surface and increases drying rate. At oven temperatures of about 82oC foam layers of many foods can be dried to about 2 to 3% moisture in approximately 12 min.
Preservation by Irradiation
            Sterilization of food by ionizing radiations is a recently developed method of preservation which has not yet gained general acceptance. The unacceptable flavour of some irradiated foods and the fear that radioactivity might be induced in such food has come in the way of its greater use.
            When gamma rays (or) electron beams pass through foods there are collisions between the ionizing radiation and food particles at atomic and molecular levels, resulting in the production of ion pairs and free radicals. The reactions of these products among themselves and with other molecules results in physical and chemical phenomena which inactivate microorganism in the food. Thus irradiation of food can be considered to be a method of ‘Cold sterilization’ i.e. food is free of microorganism without high temperature treatment. Radiation dose of upto 1 Mrad is not hazardous. 
            Ionizing radiations can be used for sterilization of foods in hermetically sealed packs, reduction of the spoilage organisms in the perishable foods, delays ripening of fruits, inhibits sprouting of root vegetables and controls infestation (insects) in stored cereals.

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PREPARATION OF JAMS, JELLIES, MARMALADES, CANDIES, CRYSTALLIZED AND GLAZED FRUITS, PRESERVES, CHUTNEYS, PICKLES, KETCHUP, SAUCE, PUREE, SYRUPS, JUICES, SQUASHES AND CORDIALS
PREPARATION OF JAMS

Jam is a product made by boiling fruit pulp with sufficient quantity of sugar to a reasonably thick consistency, firm enough to hold the fruit tissues in position.  Apply, sapota, papaya, plums, mango, grapes, jack, pineapple, banana, guava and pears are used for preparation of jam. It can be prepared from one kind of fruit or from two or more kinds.In its preparation about 45% of fruit pulp should be used for every 55% of sugar.The FPO specification of jam is 68.5% TSS, 45% of fruit pulp and 0.5-0.6% of acid (citric acid) per 100 gm of the prepared product.
a) Selection and preparation of fruit    
Select good quality ripe fruits. Wash the fruits well in cold water.  Peel the fruits and remove the stones and corers present. Cut the peeled fruit into small pieces with a stainless steel knife. If the fruit is hard, it should be cut into very small pieces. Pulp the fruits by using pulper.
b) Addition of sugar and acid
c) Cooking
            Cook the mixture slowly with occasional stirring.The fruit pulp should be crushed with a laddle during cooking. Continue cooking till the temperature of the mass reaches 105.5oC.
 Sheet (or) Flake Test
            A small portion of jam is taken out during boiling in a spoon or wooden laddle and cooled slightly. It is then allowed to drop. If the product falls off in the form of a sheet (or) flakes instead of flowing in a continuous stream (or) syrup, it means that the end point has been reached and the product is ready. Otherwise boiling is continued till the sheet test is positive.
d) Packaging 
            Fill the hot jam into clean dry sterilized jars. Allow the jam to cool and fix the sterilized lid to the jar. Store in a cool place.
Process
            Ripe firm fruits → Washing → Peeling →Pulping (Remove seed and core) → Addition of sugar and acid → Boiling (with continuous stirring) → Judging of end point by further cooking upto 105oC (or) 68% TSS (or) by sheet test → Filling hot into sterilized bottles → cooling → Sterilized bootles → cooling → Waxing → Capping → Storage (at ambient temperature).
PREPARATION OF JELLY
            A jelly is a semi solid product prepared by boiling a clear, strained solution of pectin containing fruit extract, free from pulp, after the addition of sugar and acid. A perfect jelly should be transparent, well set but not too stiff, and should have the original flavour of the fruit. It should be of attractive colour and keep its shape when removed from the mould. It should be firm enough to retain a sharp edge but tender enough when it is pressed. It should not be gummy, sticky or syrupy or have crystallized sugar.The product should be free from dullness with little (or) no syneresis (weeping) and neither tough nor rubbery. The FPO specification for jelly is the final product should have 65% solids, 45% fruit extract and 0.5-0.75% acid.
            Guava, sour apple, plum, karonda, wood apple, papaya and jack fruit are rich in pectin and generally used for preparation of jelly. Pineapple, strawberry grapes etc. can be used but only after addition of pectin powder, because these fruits have low pectin content. Preparation of jelly is similar to that of jam.
 Process
            Fruit (Firm, not over ripe) → Washing → Cutting into thin slices → Boiling with water (1 ½ times the weight of fruits for about 20-30 min) → Addition of citric acid during boiling (2 g per kg of fruit) → Straining of extract → Pectin test (for addition of sugar) → Addition of sugar → Boiling → Judging of end point (sheet / drop / temp test)  → Removal of scum (or) foam (one teaspoonful of edible oil added for 45 kg sugar) → Addition of colour and remaining citric acid → Filling hot into clean sterilized bottles → Waxing (paraffin wax) → Capping → Storage at ambient temperature.
Important considerations in jelly making
            Pectin, acid, sugar (65%) and water are the four essential ingredients. Pectin test and determination of end point of jelly formation are very important for the quality of jelly.
PREPARATION OF MARMALADE
            This is a fruit jelly in which slices of the fruit (or) its peel are suspended. The term is generally used for products made from citrus fruits like oranges and lemons in which shredded peel is used as the suspended material. Citrus marmalades are classified into (1) jelly marmalade (2) jam marmalade. The FPO specifications for marmalade are TSS- 65% and fruit juice – 45% of the prepared product.
Ingredients
Pectin extract – 1 litre
Sugar – 750 gm
Shredded peel – 62 gm
Jelly marmalade
It prepared from the clarified pectin extract.
 Process 
Ripe fruits → Washing → Peeling outer yellow portion (Flavedo) thinly → Cutting yellow portion into fine shreds (1.9 – 2.5 cm long and 0.8 – 0.12 cm thick)  Cutting of 0.3-0.45 cm thick slices of peeled fruit (or) crushing into pulp in a greater → Boiling (in 2-3 times its weight of H2O for 40-60 min.) Straining the extract  Testing for pectin content (alcohol test) → Addition of sugar (as required)   Cooking to 103-105oC (Continuous stirring)  Addition of prepared shreds (shredded peel boiled for 10 to 15 min. in several changes of water for softening and removing bitterness and added @ about 62 g per kg of extract)  Boiling till jellying point (continuous stirring)  Testing for end point (sheet / drop / temp. test)  Cooling (to 82-88oC with continuous stirring)  Flavouring (orange oil)  Filling in sterilized bottles → Sealing → Storage at ambient temperature.
Jam Marmalade
            The method of preparation is practically the same as that for jelly marmalade. In this case the pectin extract of fruit is not clarified and the whole pulp is used. Sugar is added according to the weight of fruit, generally in the proportion of 11. The pulp – sugar mixture is cooked till the TSS content reaches 65%.
PREPARATION OF CANDIED FRUITS / VEGETABLES
            A fruit /vegetable impregnated with cane sugar (or) glucose syrup and subsequently drained free of syrup and dried is known as candied fruit / vegetable. The most suitable fruits for candying are amla, kranda, pineapple, cherry, papaya, apple, peels of orange, lemon, grape fruit and ginger etc. The FPO specifications for candied fruits are TSS -75%, total sugar-70% and reducing sugar-25%.
            The process for making candied fruit is practically similar to that for preserves.The only difference is that the fruit impregnated with syrup having a higher percentage of sugar – 75obx.The syrup left over from the candying process can be used for candying another batch of the same kind of fruit after suitable dilution, for sweetening chutneys, sauces and pickles and vinegar making.
PREPARATION OF CRYSTALLIZED FRUITS /VEGETABLES
Candied fruits /vegetables coated with crystals of sugar, either by rolling in finely powdered sugar or by allowing sugar crystals from dense syrup to deposit on them are called crystallized fruit / vegetable.

The candied fruits are placed on a wire mesh tray which is placed in a deep vessel. Cooled syrup (70% TSS) is gently poured over the fruit so as to cover it entirely. The whole

mass is left undisturbed for 12-18 hrs during which a thin coating of crystallized sugar is formed. The tray is then taken out carefully from the vessel and the surplus syrup dried off. The fruits are then placed in a single layer on wire mesh trays and drained at room temperature or at about 49oC in driers.
PREPARATION OF GLAZED FRUITS /VEGETABLES
Covering of candied fruits / vegetables with a thin transparent coating of sugar, which imparts them a glossy appearance is known as glazing.
Cane sugar and water (21 by weight) are boiled in a steam pan at 113-114oC and the scum is removed as it comes up. Thereafter the syrup is cooled to 93oC and rubbed with a wooden laddle on the side of the pan when granulated sugar is obtained. Dried candied fruits are passed through this granulated portion of the sugar solution, one by one, by means of fork and then placed on trays in a warm dry room. They may also be dried in a drier at 49oC fir 2-3 hrs when they become crisp, they are packed in airtight containers for storage.
Preparation of Preserves
            A mature fruit / vegetable (or) its pieces impregnated with heavy sugar syrup till it becomes tender and transparent is known as preserve. Aonla, apple, pear, mango, cherry, karonda, strawberry, pineapple, papaya, carrot etc. can be used for making preserves. FPO specifications for preserve is TSS 68obx and fruit pulp – 55%.
General considerations
            Cooking of fruit directly in syrup causes shrinking of fruit and reduces absorption of sugar. Therefore, the fruit should be blanched first to make it soft enough to absorb water, before steeping in syrup. However, highly juicy fruits may be cooked directly.
            Fruits may be cooked in syrup by three processes as given below
i. Rapid process
Fruits are cooked in low sugar syrup. Boiling is continued with gentle heating until the syrup becomes sufficiently thick. Soft fruits such as strawberries, grapes which require very little boiling for softening.  Unlike hard fruits like apples, pears and peaches, which require prolonged heating. Rapid boiling should, however be avoided as it makes the fruit tough, especially when heating is done in a large shallow pan with only a small quantity of syrup. The final concentration of sugar should not be less than 68% which corresponds to a boiling point of 106oC. This is a simple and cheap process but the flavour and colour of the product are lost considerably during boiling.
ii. Slow process
            The fruit is blanched until it becomes soft. Sugar, equal to the weight of fruit, is then added to the fruit in alternate layers and the mixture allowed to stand for 24 hrs. During this period, the fruit gives out water and the sugar goes into solution, resulting in a syrup containing 37-38% TSS. Next day, the syrup is boiled after removal of fruits to raise its strength to about 60% TSS. A small quantity of citric acid (1 to 1.5 g/kg  sugar) is also added to invert a portion of the cane sugar and thus prevent crystallization. The whole mass is then boiled for 4-5 min. and kept for 24 hrs. On the third day, the strength of syrup is raised to about 65% TSS by boiling. The fruit is then left in the syrup for a day. Finally, the strength of the syrup is raised to 70% TSS and the fruits are left in it for a week. The preserve is now ready and is packed in containers. This method is usually practiced.
3. Vacuum process
            The fruit is first softened by boiling and then placed in the syrup which should have 30-35% TSS. The fruit-syrup blend is then transferred to a vacuum pan and concentrate under reduced pressure to 70% TSS. Preserves made by this process retain the flavour and colour of the fruit better than by the other two methods.
            In all these processes, the fruit is kept covered with syrup during cooking as well as afterwards otherwise it will dry up and the quality of the product would be affected.
            The product should be cooled quickly after the final boiling to prevent discolouration during storage.
            The fruits are drained free of syrup and filled in dry containers or glass jars. Freshly prepared boiling syrup containing 68% TSS is then poured into the jars / containers which are then sealed airtight. In the commercial scale production, however, it is better to strerilize the cans to eliminate any possibility of spoilage of product during storage.
Process
Mature fruits → Washing → Preparation of fruit for sugar treatment → Keeping fruit and sugar in alternate layers (1.0 kg Fruit: 1 kg Sugar) (or) steeping fruit in syrup of 40% TSS for a day → Removal of fruit →  Increasing consistency of syrup to 60% TSS by boiling  Steeping of fruit for a day →Repeating the process and raising strength of syrup by 5% TSS to 70% on alternate days – Steeping in 70% TSS for a week → Preserve – Draining – Filling in jar (or) container → Covering fruit with freshly prepared sugar syrup of 68% TSS   Sealing (airtight) – Storage.
PREPARATION OF CHUTNEYS
              A good quality chutney should be palatable and appetizing. Mango chutney is an important food product exported from India to many countries. Apple and apricot chutneys are also very popular in the country.
            The method of preparation of chutney is similar to that for jam except that spices, vinegar and salt are added. The fruits / vegetables are peeled, sliced or grated or cut into small pieces and cooked in water until they become sufficiently soft. The quality of chutney depends to a large extent on its cooking which should be done for a long time at a temperature below the boiling point. To ensure proper thickening, cooking is done without a lid even though this results in some loss of volatile oils from the spices. Chopped onion and garlic are added at the start to mellow their strong flavours. Spices are coarsely powdered before adding. Vinegar extract of spices may be used instead of whole spices. Spices and vinegar are added just before the final stage of cooking, because prolonged boiling causes loss of some of the essential oils of spices and of vinegar by volatilization. In mango and apricot sweet chutneys, where vinegar is used in large quantity, the amount of sugar added may be reduced, because vinegar itself acts as a preservative. These chutneys are cooked to the consistency of jam to avoid fermentation.
Sweet mango chutney
Recipe
Mango slices (or) shreds – 1.0 kg, sugar (or) gur – 1.0 kg, salt – 45 g, onions (chopped) – 50 g, garlic (chopped)-15 g , ginger (chopped) – 15 g, red chilli powder – 10 g, black pepper, cardamom, cinnamon, cumin – 10 g each, cloves – 5 nos. and vinegar – 170 ml.
Process
            Mature mangoes → washing → Peeling →Grating (or) slicing → cooking with a little water to make highly soft → Mixing with sugar and salt and leaving for an hour → Keeping all ingredients (except vinegar) in cloth bag, tied loosely, putting in mixture and cooking on low flame →During cooking, spice bag pressed occasionally   Cooking to consistency of jam (upto 105oC) with stirring occasionally → Removal of spice bag after squeezing → Addition of vinegar → Cooking for 2-5 min. → Filling hot into bottles → Sealing (airtight) → Storage at ambient temperature.

PREPARATION OF PICKLES         
            The preservation of food in common salt (or) in vinegar is known as pickling. It is one of the most ancient methods of preserving fruits and vegetables. Pickles are good appetizers and add to the palatability of a meal. They stimulate the flow of gastric juice and thus helps in digestion.
Preservation by salt  (NaCl2)
Sodium chloride is an indispensable component of food. At lower concentrations it contributes significantly to the flavour.  At higher concentrations it exhibits an important bacteriostatic action. Salt is easily available and not expensive.
Pickling process
            Pickling is done in two stages (1) By curing (or) fermentation with dry salting (or) fermentation in brine (or) salting without fermentation (2) By finishing and packing.
            Pickling is the result of fermentation by lactic acid forming bacterial which are generally present in large numbers on the surface of fresh vegetables and fruits. Theses bacteria can grow in acid medium and in the presence of 8-10% salt solution whereas the growth of a majority of undesirable organisms is inhibited. Lactic acid bacteria are most active at 30oC, so this temperature must be maintained as far as possible in the early stage of pickle making. When vegetables are placed in brine, it penetrates into the tissues of the farmers and soluble material present in them diffuses into the brine by osmosis. The soluble material includes fermentable sugars and minerals. The sugars serve as food for lactic acid bacteria which convert them into lactic acid and other acids. The acid brine thus formed acts upon vegetables tissues to produce the characteristics taste and aroma of pickle. There are two methods for pickling
1. Dry salting method
Alternate layers of vegetables and salt (20-30 gm of dry salt/kg vegetables) are kept in a vessel which is covered with a cloth and a wooden board and allowed to stand for about 24 hrs. During this period, due to osmosis, sufficient juice comes out from the vegetables to form brine.
            The amount of brine required is usually equal to half the volume of vegetables. Brining is the most important step in pickling. The growth of a majority of spoilage organisms is inhibited by brine containing 15% salt. Lactic acid bacteria, which are salt tolerant can thrive in brine of 8-10% strength though fermentation takes place fairly well even in 5% brine. In a brine containing 10% salt, fermentation proceeds somewhat slowly. Fermentation takes place to some extent upto 15% but stops at 20% strength. It is therefore, advisable to place the vegetables in 10% salt solution for vigorous lactic acid fermentation.
            As soon as the brine is formed, the fermentation process starts and Co2 begins to evolve. The salt content is now increased gradually, so that by the time the pickle is ready, salt concentration reaches 15%. When fermentation is over, gas formation ceases.

Under favourable conditions fermentation is completed in7-10 days. When sufficient lactic acid has been formed, lactic acid bacteria cease to grow and no further change takes

place in the vegetables. However, precautions should be taken against spoilage by aerobic microorganisms, because in the presence of air, pickle sum is formed which brings about putrefaction and destroys the lactic acid. Properly brined vegetables keep well in vinegar for a long time.
II. Fermentation in brine
Steeping of the vegetable in a salt solution of pre-determined concentration for a certain length of time is called brining. This type of treatment is adopted in the case of cucumbers and similar vegetables which do not contain sufficient juice to form brine with dry salt. Brine can be prepared by dissolving in common salt in water and filtering it through the cloth to remove insoluble impurities. The remaining process is similar to that of dry salting method.
 Raw materials used in pickling
1. Salt:  Free from impurities, and salts such as lime (CaO), iron (blackening), magnesium (results bitter taste) and carbonates (makes the pickle soft in texture).
2. Vinegar:  Vinegar of good quality should contain atleast 4% acetic acid. Synthetic vinegar (or) low quality vinegar are not suitable for pickle preparations. Usually malt (or) cider vinegar is used. In order to ensure good keeping quality pickle, the final concentration of acetic acid in the pickle should not be less than 2%. Acetic acid (commercial) is also used because it is highly concentrated.
3. Sugar:  Used in the preparation of sweet pickles should be of high quality.
4. Spices: Spices are added practically to all pickles, the quantity added depending upon the kind of fruit (or) vegetable taken and the kind of flavour desired. The spices generally used are bay leaves, cardamom, chillies, cinnamon, clove, coriander, dill herb, ginger, mace, mustard,black pepper, cumin, turmeric, garlic, mint, fenugreek, asafoetida etc.
5. Water: Only potable water should be used for the preparation of brine. Hard water contains salts of Ca, Na, Mg etc., which interfere with the normal salt curing of the vegetable. If hard water is to be used, a small quantity of vinegar should also be added to the brine the neutralize its alkalinity. Iron should not be present in the water in any appreciable quantity as it causes the blackening of the pickle.
6. Cooking utensils:  Metallic vessels should be non-corrodiable. Vessels made of iron (or) copper are not suitable. Glass -lined vessels, and stainless steel vessels are preferred. The laddles, spoons and measuring vessels should also be masde on non-corrodible materials. At present, pickles are prepared with salt, vinegar, oil (or) with a mixture of salt, oil, spices and vinegar. These methods are discussed below
I. Preservation with salt
            Salt improves the taste and flavour and hardens the tissues of vegetables and controls fermentation. Vegetables do not ferment when they are packed with a large quantity of salt. Spoilage is prevented by adding sufficient common salt, bringing its final concentration in the material from 15-20%. At this high salt concentration, mould and even lactic acid forming bacteria do not grow. This method of preservation is applicable only to vegetables which contain very little sugar because sufficient lactic acid cannot be formed by fermentation to act as preservative. Some fruits like lime, mango, etc. are also preserved with salt.
Example
1. Lime pickle:  Lime – 1 kg, salt – 200 g red chilli powder –15 g, cinnamon, cumin, cardamom and black pepper (powdered) each –10 g cloves – 5 Nos.
Process
            Limes → Washing  →Cutting into 4 pieces → Squeezing out juice from ¼ amount of fruit → Mixing spices and salt with juice → Mixing with lime pieces → Filling in jars → Covering with lid → Keeping in sun for 4-6 days (shaking jar atleast twice a day) → Storage at ambient temperature.
II. Preservation with vinegar
            In vinegar pickles, vinegar acts as a preservation. The final concentration of acid as acetic acid in the finished pickle should not be less than 2%. To avoid dilution of vinegar below this strength by the H2O liberated from the tissues, the vegetables (or) fruits are generally placed in strong vinegar of about 10% acidity for several days before final packing. This treatment helps to expel the gases present in the intercellular spaces of vegetable tissues. Papaya, pears, onion, garlic, chillies, mango and cucumber pickles are prepared in this method.
Example
Cucumber pickle 
Cucumber – 1.0 kg, salt – 200 g red chilli powder – 15 g, cardamom (large), cumin, black pepper (powdered) each – 10 g, cloves –   6 Nos., vinegar – 750 ml.
Process 
Cucumbers → Washing → Peeling → Cutting into 5 cm round pieces → Mixing with salt → Filling in jar → Standing for 6-8 hrs → Draining off H2O → Adding spices and vinegar → Keeping in sun for a week → Storage.
III. Preservation with oil
The fruit (or) vegetable should be completely immersed in the edible oil. Cauliflower, lime, mango, amla, karonda, bittergourd, brinjal, turnip pickles are prepared from this method.
Example 
Green chilli pickle: Green chillies – 1 kg, salt – 150 gm, mustard (ground) – 100 gm lime juice – 200 ml (or) amchur – 200 gm, fenugreek cardamom (large), turmeric, cumin (powdered) each – 15 gm, mustard oil – 400 ml.
Process
Green chillies → Washing →Drying → Making incision → Mixing all spices in a little lime juice → Mixing with chillies → Filling into jar → Adding lime juice and oil → Keeping in sun for a week – Storage.
IV. Preparation with mixture of salt, oil, spices and vinegar
Example
Tomato pickle: Tomatoes – 1 kg, salt 75 g, garlic (chopped) – 10 g, ginger (chopped)- 50 g, red chilli powder, cumin, cardamom (large), cinnamom, turmeric, fenugreek – each – 10 g, cloves – 50 nos, asafoetida (powdered) – 2g, vinegar – 250 ml, oil – 300 ml.
Process
Tomatoes (ripe, firm and pulpy) → Washing → Blanching for 5 min → Cooling immediately in water → Peeling → Cutting into 4-6 pieces (or) mashing → Frying all ingredients in a little oil except vinegar → Mixing with pieces → Heating for 2 min → Cooling → Addition of vinegar and remaining oil → Filling in jar → Storage.
PREPARATION OF SAUCES / KETCHUPS
            There is no essential difference between sauce and ketchup. However, sauces are generally thinner and contain more total solids than ketchups. Tomato, apple, papaya, walnut, soybean etc. are used for making sauces. The FPO specifications of sauces are TSS – 25% and acidity – 1%.
            Sauces are of two kinds (i) thin sauces of low viscosity consistency mainly of vinegar extract of flavouring materials like herbs and spices and (ii) thick sauces that are highly viscous.
            Sauces / ketchups are prepared from more or less the same ingredients and in the same manner as chutney, except that the fruit or vegetable pulp or juice used in sieved after cooking to remove the skin, seeds and stalks of fruits. Vegetables and spices and to give a smooth consistency to the final product. However, cooking takes longer because fine pulp (or) juice is used.

Some sauces develop a characteristic flavour and aroma on storing in wooden barrels. Freshly prepared products often have a raw and harsh taste and have, therefore, to be matured by storage. High quality sauces, are prepared by maceration of spices herbs, fruits and vegetables in cold vinegar or by boiling them in vinegar. Thickening agents are also added to

the sauce to prevent sedimentation of solid particles. Apple pulp is commonly used for this purpose in India but starch from potato, maize, arrow root (cassava) and sago are also used.
            A fruit sauce should be cooked to such a consistency that it can be freely poured without the fruit tissues separating out in the bottle. The colour of the sauce should be bright. Sauces usually thicken slightly on cooling. By using a funnel hot ketchup is filled in bottles leaving a 2 cm head space at the top and the bottles are sealed or corked at once. The necks of the bottles when cold, are dipped in paraffin wax for airtight sealing.

Apple sauce
Recipe : Apple – 1.0 kg, sugar – 250  g, salt – 10 g, onion (chopped) – 200 g, ginger (chopped) – 100 g, garlic (chopped) – 50 g, red chillipowder – 10 g, cloves – 5 Nos. cinnamon, cardamom – 15 g (each), vinegar – 50 ml, sodium benzoate – 0.7 g/kg of finished product.
Process
Apples → Washing → Peeling → Removal of core and seeds → Making into fine pulp → Straining of pulp → Cooking pulp with one third quantity of sugar → Putting spice bag in pulp and processing occasionally → Cooking to one – third of original volume of pulp → Removal of spice bag (after squeezing in pulp) →Adding remaining sugar and salt → Cooking to one – third its original volume → Addition of vinegar and preservative → Filling hot into bottles → Crown corking → Pasteurization at 85-90oC for           30 min. → Cooling → Storage at ambient temperature.
PREPARATION OF PUREE AND PASTE
            Tomato pulp without skin or seeds, with or without added salt, and containing not less than 9.0% of salt free tomato solids, is known as medium tomato puree’. It can be concentrated further to heavy tomato puree which contains not less than 12.0% solids. If this is further concentrated so that it contains not less than 25% tomato solids, it is known as tomato paste, on further concentration to 33% or more of solids it is called concentrated tomato paste.
            Tomato pulp is prepared from ripe tomatoes in the same manner as tomato juice. Cooking for concentration of the pulp can be done either in an open cooker or a vacuum pan. In the former most of the vitamins are destroyed and the product become brown. On the other hand, use of vacuum pans, which are extensive, help to preserve the nutrients, and also reduce the browning to a great extent. In vacuum pans the juice is boiled at about 71oC only. While cooking in an open cooker, a little butter or edible oil is added to prevent foaming, burning and sticking.
After    cooking, the total solids content of the juice is higher than required, more juice is added to lower it, if it is lower, cooking is continued till the desired concentration is reached. The endpoint of cooking puree and paste can be determined either with a hand refractometer or by measuring the volume.
Process
Tomato juice (strained) → Cooking to desired consistency (open cooker / vacuum pan) → Judging of endpoint for puree (or) paste → Filling hot into bottles or cans (82-88oC) → Sterilization in boiling water for 20 min. →Cooling → Storage at ambient temperature.
PREPARATION OF SYRUP
            This type of fruit beverage contains 25% fruit juice (or) pulp, 65% TSS, 1.3 to 1.5% acidity and 350 ppm of So2 or 600 ppm of KMS. It is diluted before serving, Fruits like aonla, jamun, pomegrante, grape, lemon, orange and sometimes ginger can be used for the preparation of syrup. It is also prepared from extracts of rose, sandal almond etc.
Synthetic syrups
            Heavy sugar syrup of 70-75 per cent strength is used as the base of all synthetic syrups and they are flavoured and coloured with artificial essence/flavours and colours. They never contain fruit pulp/juice. A large proportion of these syrups can, however, be replaced by real fruit juices, squashes and syrups which are more nutritious.
            Large quantities of synthetic syrups (orange, lemon, pineapple, strawberry) are manufactured and sold in varius countries. These can be prepared by using 1.5 kg of sugar, 500 ml of H2O and 15 g of citric acid.  Different colours and flavours are added as required. Among colours, orange red, lemon yellow, green, raspberry red etc. are mostly used, while artificial essence/flavours of rose, orange, pineapple, strawberry, lemon etc. are added as flavouring substances.
PREPARATION OF FRUIT JUICES
i. Selection of fruit:
  All fruits are not suitable because of difficulties in extracting the juice or because the juice is of poor quality. The variety and maturity of the fruit and locality of cultivation influence the flavour and keeping quality of its juice. Only fully ripe fruits are selected. Over ripe and green fruits, if used, adversely affect the quality of the juice.
ii. Sorting and washing
Diseased, damaged (or) decayed fruits are rejected or trimmed. Dirt and spray residues of arsenic, lead etc., are removed by washing with water or dilute hydrochloric acid (1 part acid 20 parts water).
iii. Juice extraction  
Generally juice is extracted from fresh fruit by crushing and pressing them. Screw type juice extractors, basket presses or fruit pulpers are mostly used.
The method of extraction differs from fruit to fruit because of differences in their structure and composition. Before pressing, most fruits are crushed to facilitate the extraction. Some require heat processing for breaking up the juice – containing tissues. In case of citrus fruits, the fruit is cut into halves, and the juice extracted by light pressure in a juice extractor or by pressing the halves in a small wooden juice extraction.  Care should be taken to remove the rind of citrus fruits completely otherwise it makes the juice bitter. Finally, the juice is strained through a thick cloth or a sieve to remove seeds. All equipments used in the preparation of fruit juices and squashes should be rust and acid proof. Copper and iron vessels should be strictly avoided as these metals react with fruit acids and cause blackening of the product. Machines and equipments made of aluminium, stainless steel etc. can be used.  Extracted juices should not be unnecessarily exposed to air as it will spoil the colour, taste and aroma and also reduce the vitamin content.
IV. Deaeration
Fruit juices contain some air, most of which is present on the surface of the juice and some is dissolved in it. Most of the air as well as other gases are removed by subjecting the fresh juice to a high vacuum. This process is called deaeration and the equipment used for the purpose is called a deaerator. Being a very expensive method, it is not used in India at present.
V. Straining (or) Filtration 
Fruit juices always contain varying amounts of suspended matter consisting of broken fruit tissue, seed, skin, gums, pectic substances and protein in colloidal suspension. Seeds and pieces of pulp and skin which adversely affect the quality of juice, are removed by straining through a thick cloth or sieve. Removal of all suspended matter improves the appearance but often results in disappearance of fruity character and flavour. The present practice is to let fruit juices and beverages retain a cloudy or pulpy appearance to some extent. In case of grape juice, apple juice and lime juice cordial however, a brilliantly clear appearance is preferred.
VI. Clarification
Complete removal of all suspended material from juice, as inlime juice cordial, is known as clarification which is closely related to the quality, appearance and flavour of the juice. The following methods of clarification are used (a) Settling (b) filtration (c) freezing (D) cold  storage (e) high temperature (f) chemicals such as gelatin, albumen, casein, mixture of tannin and gelatin (g) enzymes such as pectinol and filtragol.
VII.  Addition of sugar
All juices are sweetened by adding sugar, except those of grape and apple. Sugar also acts as preservative for the flavour and colour and prolongs the keeping quality. Sugar based products can be divided into 3 groups on the basis of sugar content.
a.      Low sugar – 30 per cent sugar or below
b.      Medium sugar – sugar above 30 and below 50%
c.      High sugar – 50% sugar and above
Sugar can be added directly to the juice or as a syrup made by dissolving it in hot water, clarifying by addition of a small quantity of citric acid or a few drops of lime juice and filtering.
VIII.  Fortification
Juices, squashes, syrups etc. are sometimes fortified with vitamins to enhance their nutritive value, to improve taste, texture or colour and to replace nutrients lost in processing. Usually ascorbic acid and Beta-carotene (water – soluble form) are added at the rate of 250-500 mg and 7-10 mg per litre, respectively. Ascorbic acid acts as an antioxidant and beta-carotene imparts an attractive orange colour. For a balanced taste some acids are added. Citric acid is often used for all types of beverages and phosphoric acid for cola type of drinks.
IX. Preservation
Fruit juices, RTS and nectars are preserved by pasteurization but sometimes chemical preservatives are used. Squashes, crushes and cordials are preserved only by adding chemicals. In the case of syrup, the sugar concentration is sufficient to prevent spoilage. Fruit juice concentrates are preserved by heating, freezing or adding chemicals.
X. Preservation by Bottling
Bottles are thoroughly washed with hot water and filled leaving 1.5-2.5 cm headspace. They are then sealed either with crown corks (by crown corking machine) or with caps (by capping machine).
Individual Beverages
1. Juices
Juices are of two types
a. Natural juice (pure juice):It is the juice, as extracted from ripe fruits, and contains only natural sugars.
b. Sweetened juice: It is a liquid product which contains at least 85% juice and 10% TSS.
Pure fruit juices such as apple juice and orange juice are commercially manufactured. Apple juice is generally bottled while other juices are canned.
Example Apple juice
Apples → Washing with 1.5% Hcl – Grating (apple grater)→ Crushing for juice extraction → Straining → Clarification (By enzyme (or) gelatin) → Filtration→ Heating at 82-85oC → Filling hot into cans →Sealing  → Processing at 100oC for 15 min. → Cooling → Storage.
Citrus juice
            Mandarin and sweet oranges → Washing → Peeling (By hand) →  Separation and cleaning of segments → Juice extraction (Screw type extractor) → Straining → Heating at 80oC – Bottling (or) canning (Baby food cans) → Crown corking (or) can sealing →Pasteurization → Cooling → Storage.
Example for sweetened juice
Mango juice
Mangoes (ripe) →  washing → peeling   stone removal →straining of pulp – addition of water (1 lit pulp  0.5 lit H2O) → mixing with syrup → Homogenization → Heating at 85oC → Filling hot into cans → sealing → Processing at 100oC for 20 min → cooling → storage.
2. Ready-to-serve (RTS)
            This is a type of fruit beverage which contains atleast 10% fruit juice and 10% total soluble solids besides about 0.3 per cent acid. It is not diluted before serving hence it is known as ready to serve.
            Commercially RTS beverages (with 13% TSS and 0.3 % acid) can be prepared by using SO2 -70 ppm or benzoic acid 120 ppm.
For example:  Papaya RTS
Ripe fruits → Washing → Peeling → Cutting into halves → Seed removal → Passing through pulper → Pulp → Mixing with strained syrup solution (Sugar + Water acid, heated just to dissolve) Homogenisation → Bottling → crown corking → Crown corking → Pasteurization (about 90oC for 25 min) – Cooling →  Storage.
PREPARATION OF SQUASH
            This is a type of fruit beverage containing atleast 25 per cent fruit juice (or) pulp, 45% TSS, 1.0% acidity and 350 ppm of So2 (or) 600 ppm of sodium benzoate. It is diluted before serving (13). Lime, mango, orange and pineapple are used for making squash commercially using KMS as preservative or fruits viz. jamun, passion fruit, raspberry, strawberry, grape fruit etc. with sodium benzoate as preservative.
PREPARATION OF CORDIAL
            It is a sparkling, clear, sweetened fruit juice from which pulp and other insoluble substances have been completely removed. It contains atleast 25% juice, 30% TSS, 1.5% acid and 350 ppm of So2.This is very suitable for blending with wines. Lime and lemon are suitable for making cordial.
Process 
Fruits → Washing → Cutting into halves →Juice extraction → Straining →Addition of preservative (kms/gm/litre juice) → Storing in glass container for 10-15 days for clarification (suspended material settles down)  → Syphoning off the suspernatant clear juice → Straining and measuring → Preparation of Syrup → Straining → Mixing of juice with syrup → Addition of preservative → (KMS 0.6 g / lit product) → Bottling → Capping → Storing in cool and dry place.

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SPOILAGE OF CANNED PRODUCTS – BIOCHEMICAL, ENZYMATIC AND MICROBIAL SPOILAGE
SPOILAGE OF CANNED PRODUCTS
Enzymatic spoilage

Many reactions in plant and animal tissues are activated by enzymes. The changes in foods during storage can be produced both by enzymes present in the food or by enzymes from microorganisms that contaminate the food. A good example of the former is the ripening of banana due to the enzymes present which hasten the ripening process. After some time the fruit become too soft and unfit to eat. If there is a bruised spot on the fruit, yeasts can grow and produce enzymes which spoil the fruit.
            Enzymes convert starch into sugars, protein into amino acids, and pectin into pectic acids and thus change the constituents of food. Some fruits and vegetables turn brown when damaged or when their cut surfaces are exposed to air due to the presence of the enzymes phenolase, peroxidase and polyphenol oxidase. Their actions can be easily controlled by regulating the temperature and excluding moisture and air. Enzyme can act between zero and 60oC. the optimum temperature of reaction is usually 37oC, the rate varying directly with temperature. All enzymes are inactivated at 80oC.
Microbial spoilage
            Bacteria, yeasts and moulds may infect food after harvesting, during its handling, processing and storage. But not all microorganisms cause spoilage, e.g., lactic acid bacteria are used in the making of cheese and other fermented dairy products, yeasts for the production of wine and beer and Acetobacter bacteria for vinegar production. Spoilage organisms are present everywhere- in soil, air, water and even in the raw and processed food.
(i) Bacteria
            These are unicellular microorganisms that are classed as plants though they do not contain chlorophyll. A bacterial cell is about I m in length and somewhat smaller in diameter. Bacteria are classified according to their shape. Cocci are spherical, bacilli are cylindrical and spirilla and vibrios are spiral. Bacterial spores are more resistant than yeast or mould spores to most processing conditions. Bacteria, with a few exceptions, cannot grow in acid media in which yeasts and moulds thrive. They multiply by ‘fission’ or division of cells. When a bacterium becomes mature it divides into two, these two become four and so on. The growth of bacteria is very rapid and depends upon the nature of the food material, moisture, temperature and air. Some bacteria do not grow in air but temperature plays a major role in their growth, the optimum being generally 37oC.
            Some bacteria produce spores which can be destroyed by heating at 121oC for 30-40 minutes. Bacteria are very sensitive to acids and are destroyed in their presence even at the temperature of boiling water. Hence, most fruits being acidic can be easily sterilized at 100oC whereas vegetables being non-acidic require a higher temperature of 116oC. The important groups of bacteria are:
(a) Bacillus:  rod-shaped;
(b) Coccus:  spherical;
(c) Coccobacillus:  oval-shaped;
(d) Aerobes :require atmospheric oxygen for growth, e.g., Acetobacter aceti;
(e) Facultative anaerobes: can grow with or without atmospheric oxygen;
(f) Obligate anaerobes: do not grow in atmospheric oxygen;
(g) Mesophiles: require a temperature below 38oC for growth;
(h) Obligate thermophiles: grow between 38 and 82oC;
(i) Facultative thermophiles: grow over the whole range of temperature covered by mesophiles and obligate thermophiles and below; and       
(j) Psychrotrophs: grow fairly well at refrigeration temperatures and some can even grow slowly at temperature below freezing.
Important Food Spoilage Bacteria

Some useful bacteria
            The following bacteria are of great importance in the food processing industry.
Acetobacter sp.
            These bacteria, also known as “Vinegar bacteria”, cause significant spoilage in the wine industry but are necessary for vinegar production. The important species are Acetobacter aceti, A. orleansis and A. Schutzenbachi. They are very small, usually non-motile and generally do not form spores. These bacteria are aerobes and in the presence of oxygen convert ethyl alcohol to acetic acid. They are of two types-one type forms a tough shiny film on the surface of wine and the growth is known as “vinegar mother”, while the other grows throughout the wine without forming “vinegar mother”. These bacteria can be easily destroyed by heating to 65oC.
Lactobacillus sp.
            Different organisms of this group, also known as “lactic acid bacteria”, have different properties but all of them produce lactic acid from carbohydrates. Those which are used in distilling and brewing industries are facultative thermophiles (heat-tolerants) which grow abundantly at 50 to 55oC and produce much lactic acid. Mesophiles are used in the preparation of pickles. Lactobacillus plantarum is generally found in pickles and olives. The other important species are Pediococcus cerevisiae, Leuconostoc mesenteroides, Streptococcus faecalis and Lactobacillus brevis. These bacteria cause “lactic souring” and spoil wines, which can be easily prevented by maintaining a sulphur dioxide concentration of 0.007 per cent in wine.
(ii) Yeasts
            Yeasts are unicellular fungi which are widely distributed in nature. They are somewhat larger than bacteria. The cell length is about 10 m and the diameter is about a third of this. Most yeasts are spherical or ellipsoidal. Yeasts that multiply by means of ‘budding’ are known as ‘true yeasts’. The bud when it becomes mature separates from the mother cell and functions like an independent organism. Yeasts grow luxuriantly at a moderate temperature in a solution of sugar in plenty of water. Under suitable conditions the sugar is converted into alcohol and carbon dioxide gas is evolved.
          Yeast + Sugar                Alcohol + Carbon dioxide ­
            This is the reason that carbon dioxide is evolved from food materials spoiled by yeasts and pushes out corks from bottles with great force. Active fermentation can be easily recognized by the formation of carbon dioxide foams or bubbles. Yeasts prefer a low concentration of sugar for their growth. Most of them do not develop in media containing more than 66% sugar or 0.5% acetic acid. Boiling destroys the yeast cells and spores completely. Some of the yeasts which grow on fruits are Saccharomyces, Candida and Brettanomyces.
Pseudo-yeasts
            These are like true yeasts but do not form spores. All the members of this group are particularly unsuitable for fermentation purposes as they produce off-flavours and cloudiness.
Yeasts causing food spoilage

  (iii) Moulds
            Moulds are multicellular, filamentous fungi belonging to the division Thallophyta but are devoid of chlorophyll. They are larger than yeasts. They are strict aerobes and require oxygen for growth and multiplication and tend to grow more slowly than bacteria.
            The principal parts of a mould are a web-like structure known as mycelium and the spore. The mycelium is often white and cottony and penetrates into the attacked foodstuff. After fixing itself the mould produces viable spores which resist the unfavourable conditions after dispersal and germinate when they get favourable conditions. They thrive best in closed, damp and dark situations with an adequate supply of warm, moist air but require less free moisture than yeasts and bacteria. They prefer                      sugar-containing substances and may spoil jams, jellies, preserves and other sugar-based products. Acid medium favours their growth and, therefore, they grow well in pickles, juices, etc. This is the main reason that fruits and fruit products are attacked by moulds which not only consume nutrients present in the food thereby lowering its food value but also spoil the flavour, texture and appearance of the product. They may grow even on moist leather but do not thrive in an alkaline medium. Moulds are sensitive to heat; boiling quickly destroys both moulds and their spores. The most important moulds are;
a)     Penicillium sp. (Blue moulds),
b)      Aspergillus sp. (Black moulds),
c)      Mucor sp. (Gray moulds), and
d)      Byssochlamys fulva
a. Penicillium sp.
            These are also known as blue moulds. In the initial stage of growth they have a cottony appearance but later when the spores or conidia are formed, their appearance becomes powdery and the colour becomes blue, brown or pink according to age. The spoiled materials have a ‘mouldy’ odour and flavour.
b. Aspergillus sp.
            In the initial stages of growth it is white and cottony like Penicillium but later with the formation of spores, it becomes black and is hence known as “black mould”. Unlike Penicillium it does not produce off-odour and flavour. They generally attacks grapes and bael.
(c) Mucor sp.
            It is gray in colour and hence is known as ‘gray mould’. It is also known as ‘pin mould’ or bread mould’ because if frequently grows on moist bread. Although Mucor attacks fruits, in the preservation of fruits and vegetables it does not pose a serious problem like blue and black moulds.
(d) Byssochlamys fulva
            This mould causes spoilage of canned fruits. The infected fruits disintegrate and sometimes carbon dioxide gas is also produced. It can grow under reduced oxygen tension and the ascospores posses high resistance to heat. For destroying spores heating of the cans at 88 to 90oC is essential.
            Although the organism is not as resistant as some of the thermophiles, its control in canned foods is difficult. Canned products which cannot withstand prolonged heating without deterioration are ultimately spoiled. Association of this mould with fruit in the field has been observed. Hence the emphasis should be on eliminating the organism from the raw material itself instead of processing to destroy it in the can.
            A small number of moulds produce toxic substances, known as mycotoxins, in food. Aspergillus flavus produces aflatoxins in harvested crops, such as groundnut, which are stored in the field without drying properly.

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PRESERVATIVES, COLOURS PERMITTED AND PROHIBITED IN INDIA

PRESERVATIVES
Any substance which is capable of inhibiting, retarding or arresting the growth of microorganisms is known as a preservative.

1.  It may be a chemical or a natural substance (sugar, salt, acid).
2. The term preservative includes fumigants, e.g., ethylene oxide and ethyl formate, used to control microorganisms on spices, nut and dried fruits.

Classification of preservatives

1. Class I
   1. Common salt, Sugar ,Dextrose, Glucose ,Wood smoke, Spices, Vinegar, Honey
2. Class II
   1. Benzoic acid, sulphurous acid
   2. Nitrates / nitrites of sodium/ potassium in respect of foods like ham, pickled meat.
   3. Sorbic acid- sodium, potassium & calcium salts
   4. Nisin
   5. Sodium and calcium propionate

Permissible limits of Class II preservatives  in food products (FPO)
Sulphurdioxide

 COLOURS          
Permitted Natural Food Colours (FPO-1995)
These are isolated from the natural sources/synthesized.

1. 1. 1. 1. 1. Cochineal
            2. Carotene
            3. Chlorophyll
            4. Lactoflavin
            5. Caramel
            6. Annatto
            7. Ratanjot
            8. Saffron
            9. Curcumin

Synthetic colours
Permitted synthetic food colours (FPO-1995)

• Dye should be pure & free from all harmful impurities.
• Should be in high solubility.
• Acid dyes generally more stable than alkaline ones.
• Sunlight, oxidation, reduction by metals & microorganisms affect dyes.
• Degrade by thermal processing.

• Colour should not contain more than

                        Copper                        – 10  ppm
Chromium                   – 20 ppm
Arsenic                        – 1 ppm
Lead                            – 10 ppm

• Available in the form of powder / ready-to-use solutions.
• Prevent sedimentation – glycerine is added to the solution to increase density.
• Permitted level in fruit products – 0.2 /kg
• Synthetic colour preserved by addition of
  • • Alcohol            –  10%
    • Glyerine          –  25%
    • Citric acid        –  12.1%
    • Tartaric acid    –  15.6 %

Banned colours (Public Health Regulations, 1925)
Metallic colours
Antimony, arsenic, cadmium, chromium, copper, mercury, lead & zinc.
Vegetable colouring matter
            Gamboge.
Coal tar colours
            Picric acid, victoria yellow, manchester yellow, aurantia & aurine.
Other colour
Magetna-II & blue V.R.S, red 6B, Red FB & brilliant black. 

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