I UG Food Preservation

Dr Ambedkar Government Arts College , Vyasarpadi, Chennai - 39 I B.Sc - Home Science - Nutrition , Food Service Management and Dietetics (UG) 2020-2021 Major paper FOOD PRESERVATION AND PROCESSING Unit - I Nature of harvested crop • The quality of harvested crop is dependant on the conditions of growth and on post harvest treatment. Storage condition of a crop is dependent on the function of composition, resistance to attacks by microorganisms, external conditions of temperature and gases in the environment • The most important characteristic of freshly harvested fruits and vegetables is that they are alive and respiring. • Ripening rendering the produce edible; as indicated by by taste. During ripening, starch is converted to sugar. When respiration declines, senescence (it ends at the death of the tissue of the fruit) develops in the last stage. • Maturity is indicated by skin colour, optical methods, shape, size, aroma, fruit opening, leaf changes and firmness. • Low temperature also disrupt the complex sequence of biochemical reactions taking place in plant tissue and cause a disorder known as chilling injury. • After harvesting decline in the rate of oxygen uptake and Carbon dioxide evolution to a low value is followed by a shark rise to a peak, terminating in pest- climacteric stage. The peak to minimum ratio tends to increase with temperature. this ratio varies among fruits. the slope of the rise varies with species maturity, temperature and the oxygen and Carbon dioxide of the storage chamber. Plant product storage Fresh fruits and vegetable maintain life processes during storage. As long as they are alive, they are able to resist the growth of spoilage organisms to some degree. Crop treatment Apple sodium -o- phenylphenate Banana thiabendazole benomyl Grape sulphur di oxide fumigation Potato hypochlorite vegetables chloramines • Antimicrobial agents and senescence inhibitors can be used to delay the onset of spoilage in storage. The storage life varies with the rate of respiration. • Higher temperature are injurious to foods. lower temperature are effective in reducing the rate at which respiration occurs. • The temperature near 0 - 5 degree prolongs the prolongs the storage period. Animal product storage • Microorganisms causing spoilage of animal product requires 20- 30 degree Celsius for their growth, they grow best at room temperature. • Psychrotropic bacteria increases at the temperature of of 3-5 degree celsius. Survival is hindered when the temperature is raised from 8 degree celsius to 10 degrees celsius. • The spoilage of egg depend upon the degree of refrigeration. Bacterial species dominate at 5 degree celsius and a decrease was noted when the temperature reaches 20 degree celsius. • Meat must be refrigerated at all stages from butchering to eating. Meat must be maintained below 4 degree celsius to prevent spoilage. If required for a long period, freezing, canning, irradiation, drying and curing methods can be used. The heat present in freshly killed animals must be removed rapidly to avoid decomposition. • Storage of fish in ice slows the process. Effect of cold storage on quality • When foods are placed on cold storage shelf life is increased. Perishable foods on cold storage to be consumed shortly after removal from storage rooms. • It is necessary to refrigerate fruits and vegetables in separate storage chambers. when placed together cross transfer of odour occurs. Example: Apple should not be stored with celery and onions because they damage each other’s food quality . • Eggs stored with fish or vegetable lead to off flavoured eggs. • Packaging is an important area. It is needed for the the protection of food, economy of the package , convenience of the package and its appearance. Compression test, Standard method, drop test impact and vibration test on used to determine the quality of the food packed containers. Quality is hampered when food is harvested, gathered or slaughtered in a decayed condition. • Foods can be stored when their environment is altered. Cold storage is modified environment in which we place foods. The storage chamber is a large package. pre-packing perishable foods is an application of of controlled environment. The ability to control moisture in foods improves distribution and marketing. Storage of grains High moisture in foods increases storage hazards. Control measures need to be taken to ensure grains are stored in an environment which is free from all factors leading to its destruction. Strict cleaning procedures need to be carried out before storing grains. Also, care needs to be taken to check if grains have been dried completely in sunlight and then in shade. The factors affecting the grain storage are: Bulk storage It is a man made ecological system in which living organism and their non living environment interact. Deterioration results from interactions among physical, chemical, and biological variables. The environment of the grain includes physical variables such as temperature carbon dioxide, oxygen and moisture. The major biological variables include fungi, bacteria, anthropoids such as insects and mites, vertebrates such as rodents and birds. The increase in relative humidity of the atmosphere can result in large rise in grain moisture content. Temperature Heat from external sources penetrate slowly into the grain bulk. daily temperature fluctuation rarely affect the grain. Mites do not develop below 5 degree Celsius nor insects below 15 degree celsius, fungi do not develop below zero degree Celsius. Moisture It is critical in controlling the development of bacteria, actinomycetes, fungi and insects. Moisture content of grain below 13% arrest the growth of most micro-organisms and mites. Moisture content below 10 %limits development most stored grain insect & pest. weather with change in pressure the grain bulk breathes by taking in fresh air and releasing inter granular air.All this effect the storage. Respiration The respiration of the grain and the micro-flora it contains are also important in understanding deterioration. With respiration, loss of weight, grain in the moisture content, raise in the level of carbon di oxide in the air and a rise in temperature of the grain. Chemical aspects Grain can be stored with minimum quality loss if oxygen is excluded or manipulated by the structural modification of the granary. Control of insects and mites The protection of grains from destruction by insects and mites depends largely on chemical treatments. Fumigation is done to eliminate infestation and residual pesticides to protect from pest invasion. Fumigants penetrate into place that are inaccessible to liquid or solid pesticides. Importance of food storage It is necessary to store food, listed below are a few points f the same: • Storing food is economical to the consequences that can be caused otherwise. • Food Corporation of India(FCI) buys grains from farmers and stores in warehouses to be able to supply food hence meeting the ever-growing demand • Increases the shelf-life of a food item. There are different ways of storing various food items. For example, food item such as meat requires to be stored in the refrigerator as they tend to decay quickly because of its high moisture content • Proper storage enables uniform distribution of produce throughout the year • Useful in case of emergencies such as famines Water activity Water activity is defined as the ratio of the vapor pressure of water in a material (p) to the vapor pressure of pure water (po) at the same temperature aw = p/po Water is an important constituent of all foods. The minimum water activity is the limit below which a microorganism or group of microorganisms can no longer reproduce. For most foods, water activity is in the range of 0.6–0.7. Pathogenic bacteria cannot grow below a water activity of 0.85– 0.86, whereas yeast and molds are more tolerant of a reduced water activity of 0.80, but usually no growth occurs below a water activity of about 0.62. The critical limits of water activity may also be shifted to higher or lower levels by other factors, such as pH, salt, antimicrobial agents, heat treatment, and temperature to some extent. Removing water, adding solutes, or change of solute– water interactions can reduce the water activity of a food. Unit - II Pasteurization Pasteurization is a heat treatment that kills part but not all the micro organisms present and involves the application of temperatures below 100°C. The heating, may be by means of steam, hot water, dry heat or electric currents and the products are cooled immediately after the heat treatment. Milk is usually pasteurized. Pasteurized products are not sterile. They contain vegetative organisms and spores which are still capable of growth. Hence many pasteurized foods must be stored under refrigeration. Pasteurized milk can be stored for over a week under refrigeration while pasteurized milk stored at room temperature will spoil within a day. Table 2 The Time and Temperature for the Patseurization of Various Food Products Food Temperature (°C) Duration 62.8 30 mts. Milk 71.7 15 sec. 71.1 30 mts. Ice cream mix 82.2 60–20 secs. Grape wine 82–85 1 min. Dried fruits 65.6–85 30–90 mts. Bottled grape juice 76.7 30–90 mts. Carbonated juices 65.5 30 mts. Blanching Blanching is a heat treatment like pasteurization. It is done by dipping the products in boiling water for two to three minutes at 180°F to 190°F. Blanching focuses on deaerating the product and inactivating degradative enzymes before further processing. Blanching is an important step in freezing food, as frozen foods can develop off flavour, vitamin losses and colour changes while in storage. Blanching • Prevents bacterial growth. • Fixes the natural colour of vegetables – holds the colour. • Shrinks the product, better for filling the container. Canning Canning involves the application of temperatures to food that is high enough to destroy essentially all micro organisms present.

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