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 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. It also involves airtight sealing in sterilized containers to prevent recontamination. The degree of heat and the length of time of heating vary with the type of food and the kinds of micro organisms. Large quantities of food are canned for preservation. In developed countries, canned foods form a major part of the diet of the people. Items often canned are meats and meat products, fruits and vegetables, fish products, soups, etc.

The process of canning involves the following steps:

• Receiving, cleaning, grading and inspecting of raw commodity. Blanching to inactivate enzymes. Placing in the container with added brine or syrup and deaeration of the product.

• The next process is exhausting. Exhausting is done to expel the air and gas from the can so that it’s internal pressure, after heating and cooling, is the same as the atmospheric pressure.

• After exhausting, the filled cans are permanently sealed mechanically.

• The sealed containers are subjected to high temperatures, to destroy the most heat resistant organisms.

• After this, the cans are cooled by water in a cooling canal to about 38°C, before storage. The final step is casing and storing the cans

Dehydration

Dehydration is the extraction of moisture from food products like fruits, vegetables, herbs and meat. It inhibits the growth of microorganisms and imparts a long storage life. This is a modern development of and drying. Some changes that occur during the process of dehydration are: Chemical changes Browning and flavour changes Denaturation of proteins Concentration on the surface of the food (case hardening). Dehydration can be done by drying and salting. Evaporation is quickened with the addition of moderate heat which is sometimes provided by natural sunlight. The ultraviolet rays from the sun serve to kill microbes. Modern methods of dehydration use circulating air that is heated just enough to promote dehydration with- out the food. by drying is one of the oldest methods used by human beings. Drying is one of the methods used for dehydration.

Dielectric heating

The term dielectric is used to represent both the radiofrequency and microwave bands of the electro- magnetic spectrum. Radiofrequency energy is in the frequency range 1–200MHz and microwave from 300 MHz to 300 GHz. A basic radiofrequency (platen) applicator consists of two metal plates, between which the food is placed or conveyed. In radiofrequency heating, heat is generated by the passage of an electric current through the water. This is due to the presence of ions in the water, which give it a degree of electrical conductivity. In microwave heating, foods are placed in the chamber, the dipolar molecules in the water are stressed by the alternating magnetic field and this results in the generation of heat.

Dielectric heating is used for cooking, thawing, melting, and drying. The advantages of this form of heating over more conventional methods are that heat generation is rapid and occurs throughout the body of the food material. This is known as volumetric heating. Water is heated more rapidly than the other components in the food. This is an added advantage when it is used for drying foods.

Sterilisation

In sterilisation, temperatures generally range from 110 to 120°C with sterilisation times being from 20 - 40 minutes. For example, with acid fruit juices, jam, or desserts, heating to 80 – 100˚C for 10 min is normally sufficient. For killing bacterial endospores by dry heat, longer exposure times (e.g. up to 2 hours) and higher temperatures (e.g. 160 – 180˚C) are required than with moist heat. Solutions containing thermolabile compounds can be sterilised by filtration through mediums such as nitrocellulose membranes, kieselguhr, porcelain, asbestos. UV irradiation is used to keep rooms partially sterile. Bacteria and their spores are killed quickly, but fungal spores are only moderately sensitive to radiation. Ionising radiation (X ray, gamma radiation) is used to sterilise food and other compact materials. Chemical means may also be applied. Ethylene oxide is used to sterilize food, plastics, glassware, and other equipment. Generally for sterilisation, the product is canned or bottled and then heat-treated in a steriliser with steam or hot (superheated) water. Sterilisers may be batch or continuous by operated.

UHT treatment UHT treatment means a very short heat treatment at temperature of approximately 140°C (135 -150˚C) for only a few seconds. This results in a sterilised product with minimal heat damage to the product properties. UHT treatment is only possible in flow-through equipment. The product is thus sterilised before it is transferred to pre-sterilised containers in a sterile atmosphere. This requires aseptic processing. For UHT treatment, indirect heating in plate and frame or tubular heat exchangers is applied. However, direct steam injection or steam may also be applied. Extraction cooking In food processing, extraction is defined as the transfer of one or more components of a biological feed from its source material into a fluid phase, followed by separation of the fluid phase and recovery of the component(s) from the fluid. The feed is usually of plant origin, but the principles of extraction remain the same if the material is animal origin. For example, sugar is extracted from sugar beets with hot water, which yields a sucrose stream free of contaminants and of higher concentration (typically 15% sugar) than can be achieved by expression.

Retort processing of Ready to eat foods

A “Ready-To-Eat” food product may be defined as any food product which does not require any elaborate processing procedures on the part of consumer before it is good enough for consumption. It is ready-to-eat as soon as the pack is opened in a form, which is tasty and appetizing. Ready-to-Eat (RTE) and Ready-To-Serve (RTS) food - e.g. Idlis, , , meat products like pre-cooked sausages, ham, chicken products, curries, chapattis, rice, vegetables like aloo chole, navratan kurma, channa masala etc. • Ready-to-Cook food – e.g. instant mixes like cake mixes, gulab-jamun mix, falooda mix, ice- cream mix, jelly mix, pudding mix etc., pasta products like noodles, macaroni, vermicelli etc. Retort technology systems uses team or super heated water to cook food in its own package, thus extending shelf life and ensuring .

Microwave heating

Electromagnetic waves from a power source called magnetron are absorbed by the food and food becomes hot at once. Microwave cooking enhances the flavour of food because it cooks quickly with little or no water and thus preserves the natural colour of vegetables and fruits.

Merits:

1. Quick method – 10 times faster than the conventional method. So loss of nutrients can be minimized. 2. Only the food gets heated and the oven does not get heated. 3. Foods get heated uniformly. 4. Leftovers can be reheated without changing the flavor and texture of the product. 5. Microwave cooking enhances the flavor of the food because it cooks quickly with little or no water. Demerits:

1. Baked products do not get a brown surface. 2. Microwave cooking cannot be used for , or stewing. 3. Flavour of all ingredients do not blend well as the cooking time is too short.

Here food gets cooked by hot air inside the oven. Foods baked are generally brown and crisp on the top and soft and porous in the centre, (eg) cakes and breads. The temperature that is normally maintained in the oven is between 120°C–260°C.

Merits:

1. It gives a unique flavour to food. 2. Foods are made light and fluffy – cakes, rolls, custard, bread. 3. Certain foods can be prepared only by this method – bread, cakes. 4. Uniform and bulk cooking can be achieved. 5. Flavour and texture of the food is enhanced. 6. A variety of dishes can be made. Demerits: 1. Special equipment like oven is required.

2. Baking skills are necessary to obtain a product with ideal texture, Flavour and colour characteristics. Careful monitoring needed to prevent scorching.

Roasting

When food is cooked uncovered on heated metal or a , the method is known as pan- broiling, (e.g) chapathis.

Merits:

1. Quick method of cooking. 2. It improves the appearance, texture and flavor of the food. 3. Minimum oil is used. 4. Spices are easily powdered if they are first roasted. Demerits : 1. Foods can be burnt due to carelessness. 2. denatures the proteins.

Frying

Here food is cooked on a tava with little oil (eg) chapathi, cutlets, etc. Deep fat frying Food is totally immersed in hot oil and cooked. The temperature maintained is 180°–220°C (eg.) Samosa, Bajji, etc. The taste of the food is improved along with texture.

Merits:

1. Very quick method of cooking. 2. The calorific value of food is increased as fat is the medium of cooking. 3. It gives a delicious flavour and appearance to the food. 4. Taste and texture are improved. Demerits: 1. Constant monitoring is needed to prevent scorching. 2. The food may become soggy due to too much fat absorption. 3. Fried foods are not easily digested. 4. Repeated use of heated oils will have ill effects on health.

Unit -III

Refrigeration Chilling (refrigerator) temperatures are obtained and maintained by means of ice or mechanical refrigeration.

Fruits and vegetables, meat, poultry, fresh milk and milk products, fish and eggs can be preserved from two days to one week when held at this temperature. In addition to the foods mentioned above, foods prepared for serving or left-overs may also be stored in the household refrigerator. The best storage temperature for many foods, eggs for example is slightly above 00C. Low temperatures chiefly inhibit the growth of microorganisms but not permanently.

Freezing is a means of preserving food through the application and maintenance of extreme cold temperature (−4°C to −40°C). It is effective because most of the water of the food tissue is changed from the liquid to the solid state. This change in the physical state of water retards enzymatic action and stops microbial growth, the cause of food spoilage, thus preserving food. Many foods can be frozen for twelve months or more without major changes in size, shape, texture, colour and flavour.

Slow freezing process

It is also known as sharp freezing. In this method, the food is frozen under temperatures ranging from −4oC to −29oC. Freezing may require three to seventy-two hours under such conditions. Home freezing is done by this method.

Quick freezing process

The temperatures used in the quick freezing process range from −32 C to −40 C. It freezes food so rapidly that fine crystals are formed. The time taken for quick freezing is significantly lower than that of slow freezing. In quick freezing, large quantities of food can be frozen in a short period of time. The use of very low temperature for both freezing and frozen products adds to the cost but of desirable for many products in terms of retention of palatability and nutritive value.

Dehydrofreezing of fruits and vegetables is the drying of the food to about 50 percent of its original weight and volume and then freezing the food to preserve it. The quality of dehydro frozen fruits and vegetables is equal to that of fruits and vegetables which are frozen without preliminary drying. The cost is marginally less because of weight and volume savings in packing, freezing, storing and shipping.

Points to be Considered Before Freezing Food Vegetables: Blanching (dipping the products in boiling water for two to three minutes) vegetables before freezing reduces the number of microorganisms, removes some air from the tissues, makes them more compact and enhances their colour. Its most important function is to inactivate enzymes otherwise that would cause deterioration in palatability, colour and ascorbic acid content during storage.

Fruits:

The enzymes of fruits can be inactivated by blanching but it is not done as it gives the fruit a cooked flavour and soft texture. Rather fruits are cut directly into sugar syrup or sugar to prevent oxidation. Sugar not only increases the sweetness but helps to retain volatile aroma.

Meat and poultry:

Meat and poultry require only wrapping for freezing. After slaughtering the animal, the pork, meat and poultry is chilled promptly to avoid spoilage. The tendency of the fat of the pork and poultry to become rancid during storage in a freezer is aggravated by storage before freezing.

Food irradiation Food irradiation is a process of food preservation in which food is exposed to ionizing energy – radio isotope cobalt 60 and cesium-137. The electromagnetic radiation suppresses the growth of most microorganisms.

Hospitalized patients, who have compromised immune systems and astronauts in space, consume irradiated foods. More than forty years of scientific research show that this process is safe. The radiant energy kills the bacteria in the food, but it does not touch the food directly.

The uses of food irradiation are:

• To avoid the use of harmful chemical compounds in insect disinfestations of stored products and microbial decontamination of spices. • To extend the shelf life of meat, poultry and sea foods by killing microorganisms which cause spoilage. • To replace the chemicals used for slow- ing sprouting in tubers and bulbs and delay ripening of fruits.

UNIT -4 Processing and preservation by drying, concentration and evaporation: various methods sun – drying, tray or tunnel drying, spray drying, drum drying freeze drying, fluidized bed drying. Advantages and disadvantages.

Processing and preservation by drying

Dehydration is the extraction of moisture from food products like fruits, vegetables, herbs and meat. It inhibits the growth of microorganisms and imparts a long storage life. This is a modern development of smoking and drying. Some changes that occur during the process of dehydration are: Chemical changes, Browning and flavour changes, Denaturation of proteins, Concentration on the surface of the food (case hardening)

Dehydration can be done by dry-ing and salting. Evaporation is quickened with the addition of moderate heat which is sometimes provided by natural sunlight. The ultraviolet rays from the sun serve to kill microbes. Modern methods of dehydration use circulating air that is heated just enough to promote dehydration with- out cooking the food. Food preservation by drying is one of the oldest methods used by human beings. Drying is one of the methods used for dehydration.

Drying Drying is the method nature resorts to preserve foods. Natural drying was adopted by early man to dry fruits, fish and meat by exposing them to the sun.

Methods of drying

Sun drying Tray or tunnel drying, Spray drying, Drum drying Freeze drying, Fluidized bed drying.

Sun drying

Sun drying is used in many parts of the world for preserving certain foods, such as fruits and nuts. However, this method can be used only if the climatic conditions are hot with low humidity. In many cases foods are pretreated before drying to make the structure more porous and to facilitate transfer of moisture, thereby speeding the drying rate. Food porosity increases the chance of quick solubility on reconstitution, but is at a disadvantage due to increased bulk and shorter storage stability. Vegetables like beans, peas, potatoes, cauliflower, ladies finger, garlic, onion and all leafy vegetables can be sundried.

Earlier, only sun drying was used for drying. In this process, foods are directly exposed to the sun by placing them on the land or left hanging in the air. The main disadvantages of this type of drying are (i) contaminations from the environment, (ii) product losses and contaminations by insects and birds, (iii) floor space requirements, (iv) difficulty in controlling the process, and (v) bad odor. When the climate is not particularly suitable for air drying or better quality is desired, mechanical air drying is mainly used. However, sun drying is the cheapest method of drying foods. Nowadays, solar and mechanical air drying is widely used commercially.

Changes during drying

• Shrinkage occurs on the surface first and then proceeds to the inner layers. With quick high temperature drying of food, the surface becomes dry and rigid long before the center dries out.

• Dried food pieces may also contain cracks and pores of various diameters. The shrinking and pore clogging by the solutes is known as core hardening. It can be minimized by gradual drying with low surface temperature. • Foods that lack good structure and are high in sugar content, give an impres- sion of retaining moisture even after the drying process. Fruits like grapes and figs have high sugar content and lack good structure, hence appearing moist even after dehydration.

• Complete prevention of these changes is impossible. They can be minimized by using appropriate technology.

A number of drying methods are available; some are suitable for liquids, others for solid foods or mixtures containing food pieces. The common drier types used for liquid and solid foods may be categorized as the air-convection drier, drum or roller drier and vacuum drier.

Air-Convection drier – In the air-con-vection drier, hot air supplies the heat for evaporation. Though there are dif- ferent types of air-convection driers, they all have an insulated enclosure, a means of circulating air through the enclosure and a means of heating this air.

If liquid, the food may be sprayed or poured into pans or on belts. Food in the form of a fine spray or mist is introduced into a tower or chamber along with heated air. The small drop- lets come into contact with the hot air, blast off their moisture, become small particles and drop to the bottom where they are removed. This method can produce a high quality product even with heat sensitive products like milk, eggs and coffee.

Drum or Roller drier – Liquid foods, purees and mashes are dried by this method. The food to be dried is applied, as a continuous thin layer, on to the surface of a revolving drum or between a pair of drums moving in opposite directions heated by steam. The dried layer of food is scraped by a scraper blade positioned at a point on the drum. Foods that are sticky cannot be scraped when it is hot. Such a sticky food becomes brittle when cooled, which facilitates scraping. For heat resistant food products, drum drying is one of the inexpensive dehydration methods.

Vacuum driers – This method is quiet expensive but gives good quality foods. It consists of a vacuum chamber that can withstand air pressure and contains shelves to hold food. The shelves are heated. The food gets heated by conduction and radiated heat. Liquid foods dehydrated by vacuum drying have a puffed structure and are easily dis- solved in water. There is minimum flavour change and heat damage because low temperature is used in this method. Dried foods are very convenient as they are light weight, take up little storage space and can be stored for long periods as emergency foods.

Fluidized Bed Drying

This technique involves the movement of particulate matter in an upward-flowing gas stream, usually hot air. Fluidization mobilizes the solid particulates, thus creating turbulences on the solid surfaces, which increases the drying rate. The hot gas is introduced at the bottom of a preloaded cylindrical bed and exits at the top. In some cases, a vibratory mechanism is used to increase the contact of the product with the hot gas. Fluidized bed drying is usually carried out as a batch process and requires relatively small, uniform, and discrete particles that can be readily fluidized. The main advantages of fluidized bed drying are uniform temperature and high drying rates, thus less thermal damage. A rotating chamber is also used with the fluidized bed, thus increasing centrifugal force to further increase the drying rate and mixing. The use of a solid carrier, such as sea sand, and wheat bran could prevent the biomaterial from deterioration due to thermal shock.

Spray drying

Spray drying is used to remove water from a free-flowing liquid mixture, thus transforming it into a pow- der form. The fluid to be dried is first atomized by pumping it through either a nozzle or a rotary atom-izer, thus forming small droplets with large surface areas. The droplets immediately come into contact with a hot drying gas, usually air. The liquid is very rapidly evaporated, thus minimizing contact time and heat damage. Disadvantages include the size of the equipment required to achieve drying is very large and very oily materials might require special preparation to remove excessive levels of fat before atomization. Ultrasonication in the chamber can be used instead of complex atomization to produce small-diameter droplets in spray drying.

Tray drying

Cabinet- and bed-type dryers (i.e., kiln, tray, truck tray, rotary flow conveyor, and tunnel) fall into the first generation. This is the simplest drying technique, which takes place in an enclosed and heated cham-ber. The drying medium, hot air, is allowed to pass over the product, which has been placed in open trays. Convection drying is often a continuous process and is mostly used for products that are relatively low in value. Air drying is usually accomplished by passing air at regulated temperature and humidity over or through the food in a dryer. Factors that affect the rate of drying are temperature, humidity, air velocity and distribution pattern, air exchange, product geometry and characteristics, and thickness. The sample is usu-ally placed on mesh trays in one layer or in bulk on a bed or hung from a string for better air circulation over the product. Air circulation can be horizontal or vertical to the layer or bed.

Freeze drying

In freeze drying, frozen material is subjected to a pressure below the triple point (at 0°C, pressure: 610 Pa) and heated to cause ice sublimation to vapor. This method is usually used for high-quality dried products, which contain heat-sensitive components such as vitamins, antibiotics, and microbial culture. The virtual absence of air and low temperature prevents deterioration due to oxidation or chemical modification of the product. It also gives very porous products, which results in high rehydration rates. However, freeze drying is a slow and expensive process. A long processing time requires additional energy to run the com- pressor and refrigeration units, which makes the process very expensive for commercial use. Thus, it is mainly used for high-value products.

Many physical modifications are made in ingredients or foods during preservation. Such modifications can also improve the sensory, nutritional, and functional properties of foods. Changes experienced by foods during processing include glass formation, crystallization, caking, cracking, stickiness, oxidation, gelatinization, pore formation, and collapse. Through precise knowledge and understanding of such modifications, one can develop safe, high-quality foods for consumption.

CONCENTRATION

CONCENTRATION involves partial removal of moisture from liquid foods to increase their final solids upto 70%. Example : jelly and candied fruits. Foods can be stored with hermetic sealing and they are very attractive. Prevents microbial spoilage and can be preserved for a longer period of time.

Evaporation

Evaporation is a common unit operation in food processing industries in which partial removal of water takes place from an aqueous solution. The removal of water in the form of vapour is achieved by the process of vaporization or boiling of aqueous solution. Evaporation is confined to the preservation of liquid foods by concentrating them as a result, microbiological damage is checked and shelf life increased. One more advantage is the in mass and volume of material, resulting in reduced cost of packaging, storage and transportation. The application of evaporation in food industries includes concentration of aqueous solution of sugar, milk, sodium chloride, fruit juices etc. But, in processes like desalination, water is the required product.

Unit - 5

Preservation by salt, sugar and chemicals

Preservatives are chemical agents which serve to retard, hinder or mask undesirable change in food. Preservatives help in retaining the original quality of food and delaying their spoilage.

Preservatives are classified into class I and class II preservative. Class I preservatives are available at home. Class II preservatives are prepared in the industries. • Sulphur dioxide is the only permitted preservative used in the form of sulphites. • In India, sodium benzoate, sulphites and sorbic acids are permitted preservatives used in fruits and vegetables. • Dried fruits are treated with sulphur dioxide to conserve the colour and to prevent the growth of microorganisms. • Sodium benzoate is preferred to benzoic acid because of its solubility and used in tomato ketchups, sauces, jams, jellies, pickles and fruit juices.

Sorbic acid and its salts are effective against yeasts and moulds but less effective against bacteria. They are good preservatives for foods with high fat content e.g., low fat spreads and processed cheese.

Sugar is used to preserve fruits. Preserving fruits in honey to avoid spoilage is a well known practice. Nowadays jams and jellies prepared from fruits have a high concentration of sugar and it acts as a preservative. Pectin, acid and sugar are essential to prepare jam. Jam or jelly are prepared by adding commercially prepared it also reduces the cooking time. Jellies are clear substances made of fruit juice or the extract of a fruit.

Sugar acts in the following ways:

Sugar draws the water out of food therefore making it unavailable for microorganisms. As a result of water loss, microbial metabolism is stopped. Hence, the growth of microorganisms is stopped Preparation of jelly: Under-ripe fruits are used, because the pectin content is high and good acidity is essential for a good jelly. Pieces of fruit are completely immersed in water and cooked for 10–20 minutes. Hard fruits like guavas need to be cooked for 45 minutes. After the fruit is cooked, it is strained without disturbing the fruit pieces. The fruit extracts contain pectin which determines the addition of sugar. When the level of pectin is high, it needs more sugar but requires less boiling time. Rapid boiling facilitates rapid evaporation, which avoids strong flavour and darkened colour. Then the jelly is poured in bottles or moulds, and allowed to set without any disturbance.

Preparation of jam:

• Fruits like apples are cooked with skin and made into pulp with the strainer for making jam

• Equal quantities of sugar and pulp are taken to make jam.

• After it is cooked, it is transferred to a sterilized bottle and allowed to cool.

Test for doneness for jam

Sheet test – the mixture is allowed to drip from a large cool spoon. If the syrup forms a sheet instead of two separate drops, the jam is done.

Bubble test – when the end point reaches, big bubbles can be seen throughout the jam.

Plate test – set a plate in the freezer for some time. Put the jam and tilt the plate slowly. The jam should come down as a whole mass forming “U” shape. Water should not separate out.

Fork test – dip the fork into the jam or jelly. Jam of correct consistency forms a sheet between the needles of the fork.

Honey

Honey is a natural preservative in its original state and was one of the earliest preservatives used by ancient civilizations. It has a high concentration of sugar that draws out the water out of yeast or bacteria cells which contaminate the food.

High Concentration of salt

Foods are also preserved by the principle of osmotic pressure in salting and pick- ling. Most commonly used preservative is sodium chloride. Required quantity may be added to slow down or prevent the growth of microorganisms or enough to permit lactic acid fermentation to take place.

Sodium chloride preserves the food by the following principles:

• It causes the high osmotic pressure and hence plasmolysis occurs.

• It dehydrates foods by drawing out and tying up moisture, as it dehydrates microbial cell. • It ionizes to yield the chlorine ion which is harmful to organisms.

• It reduces the solubility of oxygen in the moisture.

• It sensitizes the cell against carbon dioxide.

• It interferes with the action of pro-teolytic enzymes.

• : In pickling, food is placed in edible liquids like brine, vinegar or vegetable oil which inhibit or kill microorganisms Sometimes, food is heated along with pickling agent so that it gets saturated with it.

Pickles may be broadly divided into three groups:

Sweet pickles e.g., tomato sweet pickle, mango sweet pickle.

Sour pickles e.g., mango pickle, lime pickle.

Fermented pickles e.g., cucumber pickle, cabbage pickle, chilli pickle, meat and sausages.

The important preservative agents in pickles are salt, vinegar, sugar, oil, spices and condiments. Each has a specific role in preservation.

Salt:

Salt is employed to control microbial population in foods such as butter, cheese, cabbage, olives, cucumbers, meats, fish and bread. There are four methods of salt curing; dry salting (fish), brimming (vadu manga), low salt fermentation (chilli pickle, sauerkraut from cabbage) and pickling (lime pickle). Sodium chloride or common salt is used primarily as a preservative and flavouring agent.

Vinegar:

Vinegar is a natural preservative. Vinegar is made from a two step process. The first process involves the carbohydrate being converted into alcohol by fermentation. The second step is its conversion to an acetic acid. The acetic acid in vinegar kills microbes and stops food spoilage. Pickling is a common method of using vinegar as a preservative. It is also used to improve the flavour of foods.

Spices and condiments:

These have bacteriostatic effect (slowing the growth and multiplication of microbes). The essential oil of spices is inhibitor of microorganism. The inhibitory effects of the spices differ with the kind of spice and the microorganisms being tested. Mustard flour and the volatile oil of mustard, for example, are very effective against Saccharomyces cerevisiae. In pickles like avakai and chilli pickle, mustard flour helps in the prevention of the growth of spoilage organisms in the food.

Turmeric powder, tamarind, chilli powder, asafoetida, fenugreek seed, cin- namon and cloves are usually bacterio- static. Ground pepper corn and all spices are less inhibitory than cinnamon and cloves. Extracts of these plants have been shown to be inhibitory to Bacillus subtilis and E. coli. Allicin is the active principle in onions and garlic that kills bacteria and acts against fungi.

Oil

In addition to salt and several spices, oils are used in making pickles. Spice mixtures and oil are added to the fruit or vegetable. It is allowed to ferment for a month or so. The fermentation process renders fruits soft and the fruit take on the additional aroma and flavour of the spices. Aerobic bacteria and mould growth are prevented by covering the top with oil. Properly pre- pared and stored pickles can last upto a year or more without spoilage.

Smoking of foods

Smoking is mostly done to preserve the meat. This process helps to develop flavours in it. Wood smoke contains small amounts of formaldehyde, higher aldehydes, formic acid, acetic acid and resins. These compounds have antiseptic proper- ties and destroy microorganisms present. The temperature and period of smoking vary with the type of meat. In sausages, the smoking is done for a few hours after smoking the material is packed in polythene bags and kept at refrigerated conditions.

Food additives

Substances that are added to food to maintain or improve the safety, freshness, taste, texture, or appearance of food are known as food additives. Some food additives have been in use for centuries for preservation – such as salt (in meats such as bacon or dried fish), sugar (in marmalade), or sulfur dioxide (in wine). Many different food additives have been developed over time to meet the needs of food production, as making food on a large scale is very different from making them on a small scale at home. Additives are needed to ensure processed food remains safe and in good condition throughout its journey from factories or industrial kitchens, during transportation to warehouses and shops, and finally to consumers. The use of food additives is only justified when their use has a technological need, does not mislead consumers, and serves a well-defined technological function, such as to preserve the nutritional quality of the food or enhance the stability of the food. Food additives can be derived from plants, animals, or minerals, or they can be synthetic. They are added intentionally to food to perform certain technological purposes which consumers often take for granted. There are several thousand food additives used, all of which are designed to do a specific job in making food safer or more appealing. WHO, together with FAO, groups food additives into 3 broad categories based on their function. Flavouring agents Flavouring agents – which are added to food to improve aroma or taste – make up the greatest number of additives used in foods. There are hundreds of varieties of flavourings used in a wide variety of foods, from confectionery and soft drinks to cereal, cake, and yoghurt. Natural flavouring agents include nut, fruit and spice blends, as well as those derived from vegetables and wine. In addition, there are flavourings that imitate natural flavours. Enzyme preparations Enzyme preparations are a type of additive that may or may not end up in the final food product. Enzymes are naturally-occurring proteins that boost biochemical reactions by breaking down larger molecules into their smaller building blocks. They can be obtained by extraction from plants or animal products or from micro-organisms such as bacteria and are used as alternatives to chemical- based technology. They are mainly used in baking (to improve the dough), for manufacturing fruit juices (to increase yields), in wine making and brewing (to improve fermentation), as well as in cheese manufacturing (to improve curd formation). Other additives Other food additives are used for a variety of reasons, such as preservation, colouring, and sweetening. They are added when food is prepared, packaged, transported, or stored, and they eventually become a component of the food. Preservatives can slow decomposition caused by mould, air, bacteria, or yeast. In addition to maintaining the quality of the food, preservatives help control contamination that can cause food borne illness, including life-threatening botulism. Colouring is added to food to replace colours lost during preparation, or to make food look more attractive. Non-sugar sweeteners are often used as an alternative to sugar because they contribute fewer or no calories when added to food.

Types of Examples Names Found Ingredients What They Do of Uses on Product Labels

Preservatives Prevent food spoilage Fruit sauces and Ascorbic acid, citric acid, sodium from bacteria, molds, jellies, benzoate, calcium propionate, fungi, or yeast beverages, sodium erythorbate, sodium (antimicrobials); slow baked goods, nitrite, calcium sorbate, potassium or prevent changes in cured meats, sorbate, BHA, BHT, EDTA, color, flavor, or texture oils and tocopherols (Vitamin E) and delay rancidity margarines, (antioxidants); cereals, maintain freshness dressings, snack foods, fruits and vegetables

Sweeteners Add sweetness with or Beverages, Sucrose (sugar), glucose, without the extra baked goods, fructose, sorbitol, mannitol, corn calories confections, syrup, high fructose corn syrup, table-top sugar, saccharin, aspartame, sucralose, substitutes, acesulfame potassium many processed (acesulfame-K), neotame foods Color Offset color loss due to Many processed FD&C Blue Nos. 1 and 2, FD&C Additives exposure to light, air, foods, (candies, Green No. 3, FD&C Red Nos. 3 temperature extremes, snack foods and 40, FD&C Yellow Nos. 5 and moisture and storage margarine, 6, Orange B, Citrus Red No. 2, conditions; correct cheese, soft annatto extract, beta-carotene, natural variations in drinks, jams/ grape skin extract, cochineal color; enhance colors jellies, gelatins, extract or carmine, paprika that occur naturally; pudding and pie oleoresin, caramel color, fruit and provide color to fillings) vegetable juices, saffron (Note: colorless and "fun" Exempt color additives are not foods required to be declared by name on labels but may be declared simply as colorings or color added)

Flavors and Add specific flavors Pudding and pie Natural flavoring, artificial flavor, Spices (natural and synthetic) fillings, gelatin and spices dessert mixes, cake mixes, salad dressings, candies, soft drinks, ice cream, BBQ sauce

Flavor Enhance flavors Many processed Monosodium glutamate (MSG), Enhancers already present in foods hydrolyzed soy protein, autolyzed foods (without yeast extract, disodium guanylate providing their own or inosinate separate flavor)

Fat Replacers Provide expected Baked goods, Olestra, cellulose gel, (and texture and a creamy dressings, carrageenan, polydextrose, components "mouth-feel" in frozen desserts, modified food starch, of reduced-fat foods confections, microparticulated egg white formulations cake and protein, guar gum, xanthan gum, used to dessert mixes, whey protein concentrate replace fats) dairy products

Nutrients Replace vitamins and Flour, breads, Thiamine hydrochloride, riboflavin minerals lost in cereals, rice, (Vitamin B2), niacin, niacinamide, processing macaroni, folate or folic acid, beta carotene, (enrichment), add margarine, salt, potassium iodide, iron or ferrous nutrients that may be milk, fruit sulfate, alpha tocopherols, lacking in the diet beverages, ascorbic acid, Vitamin D, amino (fortification) energy bars, acids (L-tryptophan, L-lysine, L- instant breakfast leucine, L-methionine) drinks Emulsifiers Allow smooth mixing of Salad dressings, Soy lecithin, mono- and ingredients, prevent peanut butter, diglycerides, egg yolks, separation chocolate, polysorbates, sorbitan margarine, monostearate Keep emulsified frozen desserts products stable, reduce stickiness, control crystallization, keep ingredients dispersed, and to help products dissolve more easily

Stabilizers and Produce uniform Frozen Gelatin, pectin, guar gum, Thickeners, texture, improve desserts, dairy carrageenan, xanthan gum, whey Binders, "mouth-feel" products, cakes, Texturizers pudding and gelatin mixes, dressings, jams and jellies, sauces pH Control Control acidity and Beverages, Lactic acid, citric acid, ammonium Agents and alkalinity, prevent frozen desserts, hydroxide, sodium carbonate acidulants spoilage chocolate, low acid canned foods, baking powder

Leavening Promote rising of Breads and Baking soda, monocalcium Agents baked goods other baked phosphate, calcium carbonate goods

Anti-caking Keep powdered foods Salt, baking Calcium silicate, iron ammonium agents free-flowing, prevent powder, citrate, silicon dioxide moisture absorption confectioner's sugar

Humectants Retain moisture Shredded Glycerin, sorbitol coconut, marshmallows, soft candies, confections

Yeast Promote growth of Breads and Calcium sulfate, ammonium Nutrients yeast other baked phosphate goods

Dough Produce more stable Breads and Ammonium sulfate, Strengtheners dough other baked azodicarbonamide, L-cysteine and goods Conditioners

Firming Maintain crispness and Processed fruits Calcium chloride, calcium lactate Agents firmness and vegetables Enzyme Modify proteins, Cheese, dairy Enzymes, lactase, papain, rennet, Preparations polysaccharides and products, meat chymosin fats

Gases Serve as propellant, Oil cooking Carbon dioxide, nitrous oxide aerate, or create spray, whipped carbonation cream, carbonated beverages

Use and application of enzymes and microorganism in processing

Traditionally, enzymes have been obtained by extracting them from plant and animal tissues. Examples include the protease papain, which is extracted in crude form from plant material, and is used for meat tenderization and haze reduction in beer, and the protease chymosin, which is extracted from calf stomach and is used in cheese processing to promote the coagulation of milk. This increases the costs and reduces the scalability of the process. For the above reasons, the production of enzymes by extraction from animal and plant sources is nowadays limited.

The main alternative for producing enzymes is through microbial fermentation. The advantages of this method are that the enzymes are produced in a more cost effective way, scale-up is easier, the process is more reproducible and robust, and can be used for different enzymes with certain modifications. Important criteria for selecting a particular microbial strain to produce an enzyme include that the strain must give high yields and productivities, it must secrete the enzyme into the medium, as it is significantly more cost effective than to extract it from the cells, and should have a GRAS (generally regarded as safe) status.

Enzymes Applications in food processing Microorganisms

α-Amylase Starch liquefaction, alcohol production Bacillus spp. , Aspergillus spp.

β-Amylase Maltose production, alcohol production Malt

Cellulase Fruit and vegetable processing Aspergillus spp., Trichoderma spp.

Chymosin Cheese manufacturing Calves, Aspergillus spp.

β -Galactosidase Dairy products Aspergillus spp., Kluyveromyces spp.

Glucoamylase Starch saccarificati, brewing Aspergillus spp., Rhizopus spp.

Glucose isomearse High fructose corn syrup production bacillus spp Enzymes Applications in food processing Microorganisms

Hemicellulase Bread making Aspergillus spp. , Bacillus spp. ,

Trichoderma spp. a

Lipase/esterase Cheese manufacture, milk fat modification Aspergillus spp. , Candida spp., Penicillium spp.

Pectinase Extraction and clarification of fruit juices Aspergillus spp., Penicillium spp

Pentosanase Bread making Humicola spp., Trichoderma spp.

Pullulanase Starch saccharification, brewing bacillus spp

Protease Cheese manufacture, bread making, meat Aspergillus spp, Pencillium spp, Rhizopus processing spp, Bacillus spp