PRESERVATION OF FOOD

PRESERVATION OF FOOD

                     It is often convenient to preserve foods such as fish, eggs, fruits and vegetables while they are cheap and plentiful, for use when they are not. Careful preservation of food eliminates waste which may happen otherwise during a time of glut. It also helps to prevent undue fluctuation of prices.

                      Although preservation in one form or another has been practiced throughout the world, it developed scientifically into a technology only after the First World War when it was found convenient to use preserved food for the armed forces. The technology has continued to progress, and preserved food is used by rich and poor in everyday life in the West. Easy transportation, variety in food and convenience in use have all added on to the popularity of preserved foods. The development of this technology has now made it possible to have preserved food of practically the same nutritive value and palatability standards as fresh foods.

                   The object of food preservation is to destroy or inactivate spoilage by micro-organisms. Toxins produced by them and the chemicals present which are responsible for the deterioration of food. This has to be done without affecting the palatability of the food to be preserved, its colour, flavour and nutritive value.

                     Preservation can be divided into short or long period preservation.

Short period preservation

                    All moist foods are inclined to decompose rapidly and it is often necessary  to use some temporary method of preservation to prevent food deteriorating before use. In this type of preservation the spoiling agents are not killed but their growth is retarded or inactivated for period. This is done in the following ways:

Asepsis The number of micro-organisms is reduced by

(1) Washing: Along with the dirt some of the microorganisms are removed

(2) Careful handling: Crushing and bruising of fruits and vegetables is avoided and damaged ones are discarded.

(3) Packing in sanitary packages: This reduces the number of microorganisms to a great extent. Nature preserves nuts, etc., by this method.

Low temperature (chilling or cold storage) This is keeping food at refrigerated temperature. This is not a drastic method. The food is not altered but the bacteria is held dormant. This method keeps food whole only for short periods.

              Some fruits such as bananas however, spoil under refrigeration so they must be kept at 12°C (about 54°F).

             Apples and hard fruits will keep for a long time in cold storage as long as they are wrapped in grease proof paper.

             Cold storage has been practiced for thousands of years. In old temples and caves (eg. Kanheri Caves, Bombay) one can see niches surrounded by running water to keep them cool. In Pompeii in Roman times each house had a food storage compartment cut out of rock with running water

playing on it.

By heating - Cooking of food and boiling of milk helps to preserve these longer than if left fresh.

By mild antiseptics - Sugar and salt can be sprinkled over fruits and vegetables respectively that are to be used for the next day.

By removal of air - If butter is spread over potted meat or egg is dipped in a wax emulsion it can be kept for a longer period than if untreated as the air that is necessary for growth of micro-organisms is not available.

                Waxing fruits by means of sugarcane wax is another old method which is now being revived in India and is being developed on a commercial scale in Nagpur. The purpose is to exclude air by covering fruits and vegetables with wax emulsion. The results have been very encouraging.

Long period preservation

The storage life of foods is increased for a longer period by these methods:-

Sun drying - This is perhaps the oldest method of food preservation and has been used by hunters and travelers for generations. 
                     The method of preservation is the removal of moisture to render germs inactive. It has been extensively used in India and fish, meat, vegetables and fruits have been preserved by this method; eg dried fish, such as Bombay Duck, dried game meat, lentils, peas, chilies, etc., and dried fruits and nuts such as apricots, dates, raisins, cashew nuts, etc.

Dehydration - whilst sun-drying is a method of dehydration, by using mechanical devices this process has been speeded up considerably.

                         Dehydration is the removal of moisture to the extent that mould growth does not flourish under carefully controlled conditions of air flow, temperature, and humidity, in a special piece of apparatus known as a dehydrator. By using dehydrators a more standard product is also obtained. Milk and eggs, for example, are roller-dried or spray-dried.                                  The products can be successfully reconstituted. Dehydrated vegetables such as potatoes, peas, carrots, cabbage, etc., are extensively used. All vegetables must be blanched before being dehydrated (except onion, garlic, etc). Dehydrated food can be easily transported and does not need refrigerated storage. The storage space required is also reduced.

Salting - This very often accompanies dehydration. When foods are just salted, this must be done at as low a temperature as possible. In tropical countries it must be done under refrigeration. Use salt that is as pure as possible, or else the impurities cause a bitterness in the fish or meat

being salted.

Two methods are used:

(i) Rubbing the salt on the flesh of fish or meat.

(ii) Soaking in a brine tub. This method is used particularly for tongue, beef, pig's trotters and pig's head. Sometimes the brine solution is injected into the meat. Microbes cannot grow in a strong salt medium.

Smoking - This is also a very old method of preservation. Fish or meat is exposed to the smoke of a slowly burning wood fire thus imparting a smoked flavour and assisting in the preservation of the food stuff.

                Bacterial growth is stopped by the drying of the food surface and by the antiseptic action of certain constituents of the smoke, such as creosote, formaldehyde and acetic acid.

               The wood must not contain any substance that will impart a foreign flavour to the food, nor must the temperature be too high, or else the food will become too dry, and the smoke will not be able to penetrate the food thoroughly.

Deep freeze - This does not kill germs, but prevents them from being active. This method is being used more in recent years, with the advancement in refrigeration machinery.

Freezing is a relatively simple method of preserving food and is accepted as one of the most satisfactory ways of storing perishable foods. Research done in this field has shown that freezing food is the simplest and safest method of preservation provided one follows the five cardinal points. Careful selection, proper packaging, freezing at -18°C (0°F) or lower, storage at -18°C (0°F) or lower with the minimum of fluctuation, and avoiding long storage.

         Meat, poultry, poultry products, game, fruits and vegetables and prepared and cooked foods can be preserved by this method.

         It is recommended that beef be consumed within twelve months, fresh pork within six months and ground meat, especially pork sausages, within four to six months. Pork and pork products tend to develop rancidity early and cured pork products even earlier; therefore, it is a good practice to stock only a six months’ supply of pork at one time.

                These are the five cardinal points for successful storage. They are not over-exacting and not beyond reach. It is believed that home freezer owners will be far wiser to have all their bulk processing done at the nearest commercial freezer plant and use the home unit only as a home reservoir. This will leave all processing to the professional at the plant, where adequate facilities and equipment are available, and thus relieve the householder. Where small quantities of food are to be handled, as a day's supply of peas, beans or strawberries from the garden, they may safely and without materially influencing the storage temperature.

 Hermetically sealed containers - The absence of air from any containers is a principle of food storage. This method is used for biscuits, cereal preserved food in bottles.

Canning and bottling - In this method preservation of food is done in hermetically sealed containers sterilized by heat.

The word 'canning is of American origin but is now used internationally in connection with preserving foods in tin containers. In its broader sense it also includes preservation by application of heat in glass containers as well. Tins are standardized. Al T A2/2 and A10 are the commonly used sizes in India. A10 has a capacity of about 3 liters and is used for the trade as it is an economical size.

                 The canning of vegetables, fruits, meat, fish, dairy products and most edible products cooked and uncooked, has reached a very high degree of efficiency. Each food item uses a special technique. Colouring agents if added in canned and bottled products are strictly controlled by the Food and Drugs Act. In India colouring agents are specially used for canning cherries and green vegetables.

By sugar - Food products containing 60% sugar do not ordinarily spoil. Jam, jelly, marmalade, preserves, candy fruits, fruit syrups and confectionery are preserved by this method.

Gas storage - Oxygen (air) is replaced by inert gases e.g. aerated water.

Acid - Acids preserve foods by virtue of their hydrogen ion concentration, which produces a toxic effect on microbial protoplasm. e.g., pickles in vinegar.

By spices - Essential oils of spices produce a toxic effect on microorganisms, e.g., as in pickles.

By vacuum packing - Coffee powder, milk powder, etc.

By fermentation - Alcoholic beverages, etc.

By chemical preservatives - Sodium benzoate and potassium metabisulphite are the two preservatives permitted by the Food and Drugs Act.

Irradiation - Preservation by irradiation is a new technique which is being explored at present. This is done by radiation of various frequencies ranging from the low frequency electric current to the high frequency gamma rays. In 1957 it was reported that 100 food items have been cleared for human testing. The obvious advantage of food preserved by this method is that food can be stored without refrigeration. Bacon, beans, and peaches have been kept for one year at 22°C (about 72°F) storage temperature without spoilage after irradiation treatment.

                  Ionized radiation produces some destruction of nutritive value, but not sufficient to be nutritionally significant. Experiments on irradiated powdered milk showed no loss of vitamins. This may be due to a lack of

Moisture.

                  Colour changes were noticed in strawberry and milk powder amongst the foods studied. There was some flavour change in the foods, the most noticeable being in ground beef. It is believed, however, that acceptability of the strangeness in odor will be only a matter of time.

                  Work done hitherto does prove, however, that irradiation as a form of food preservation although still in its infancy, has great possibilities.

Preservation by Antibiotics - This is another method of preservation now under study. Much work has been done on Penicillin, Streptomycin, Aureomycin, Terramycin, Chloromycetin, Subtlin, Tetracyclin.

Oxytetracyclin, Chlortetracyclin, etc.

          Eviscerated chicken dipped in Aureomycin and stored at 4.4°C (about 40°F) was found fresh 7 to 14 days longer than untreated chicken.

                Chlortetracyclin (aureomycin) is recognized as one of the most effective of the broad range of antibiotics.

                 This method is still in the experimental stage. Although food bacteriologists realize the advantage of the preservation of raw foods by means of a non-toxic antibiotic or the use of one in combination with reduced amounts of heat in the processing of canned foods, they are aware of certain problems that could arise with the use of antibiotics as preservatives.

(i) The effect of an antibiotic on a micro-organism is known to vary with the species or even with the strains of the organism. Hence the antibiotic may be effective against some spoilage organisms but not others, or against part of the population in a culture but not all.

(ii) Organisms are known to be able to adapt themselves to increasing concentrations of antibiotics, so that new resistant strains may develop. There is also the possibility that other organisms not yet significant in food spoilage but resistant to the antibiotic might assume new importance in food spoilage.

(iii) Effects of the antibiotic on the consumer, sensitization to it, changes in his intestinal flora and the development of strains of pathogen in the body resistant to that antibiotic, are all possibilities. It is, therefore, recommended that the antibiotics used for food preservation be other than those used for therapeutic reasons.