How to preserve food

The proper storage  of food

 The proper storage of food for a longer use has long been an important field for scientific investigation. Of the foods available to mankind few can be stored for any length of time without special processing and handling. Delay in the use of fresh food alters its freshness, palatability and nutritive value. Food stored without adequate process spoils and becomes unfit for use.

 Need to Preserve Food 

With the industrial revolution and the increase in the urbanization human beings have become dependant on food, prepared, shipped and stored by others. Such food stuffs are treated with chemical preservatives to retard spoilage resulting either from the growth of moulds (fungi) or bacteria or by the process of oxidation. 

Causes of Food Spoilage

 In general, food spoilage is mainly due to micro-organism (bacteria, moulds, and yeasts) and to a lesser extent by chemical reactions catalyzed by enzymes. 

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Water and Moisture (cause of food spoilage)

Water is closely linked to food spoilage. Many agricultural products of low moisture contents, such as corn and soyabean, if exposed to atmosphere of 75% relative humidity or higher may take up enough moisture content to permit the growth of moulds and bacteria. Foodstuffs with moisture below the critical level required for microbial growth, cannot be stored in a warm climate where high humidity may persist fora long period. The release of water from one piece of decaying food can increase the rate of decay of other foods close to it. 

Microbial Activities (cause of food spoilage)

Bacteria, yeast and moulds are often responsible for food spoilage. Most kinds of food are subject to microbial spoilage unless special methods are used for their preservation. Fish is spoiled chiefly by microbial growth. Undesirable changes in poultry and dairy products are brought about by the growth of micro-organisms. 

Chemical Changes(cause of food spoilage)

 Chemical changes are also responsible for food spoilage. These changes are brought by enzymes. These enzymes may have their origin in the food material or may be produced by micro-organisms such as yeast, moulds and bacteria which contaminate the product. The rancidity of fats and oils and the browning of fruits and vegetable are examples of food spoilage due to chemical or biochemical changes. The browning of fruit tissues is especially noticeable in apples. 

Methods of Preservation of Food

 A practical method of food preservation must retain, as far as possible, the original characteristic of food and it must not be harmful for health. 

Removal of Moisture(Preservation of Food)

The drying of food is an ancient method for its preservation. The presence of even a small amount of moisture will permit enzyme or microbial action which results in spoilage. During drying process many micro organisms are destroyed by heat. 

Addition of Salt or Sugar(Preservation of Food)

 The rate of food decomposition can be slowed down by using common salt or sugar. The addition of these substances increase the solute concentration in water present in food. If the cell of a micro-organism is in contact with the concentrated salt or sugar solution, it would lose water to the surrounding food. As a result the micro-organism would not be capable of multiplication and therefore would not cause food spoilage. 

Changing Temperature(Preservation of Food)

 Food can be preserved by increasing or decreasing temperature. At high temperature bacterial cells and spores are destroyed. At low temperature, both the growth of micro-organisms as well as the rate of chemical reaction which cause food spoilage are retarded.

 Chemical Additives for Food preservation

Chemical additives for food are chemical substances which are added in small amounts to preserve it. Salts of calcium, magnesium, potassium and sodium are all commonly used as food additives. Sodium sulphite and potassium metabisulphate are used as preservatives because they prevent the growth of micro-organisms. Sodium dihydrogen phosphate is used to improve the texture of foods and magnesium hydroxide is used as an alkali to reduce acidity in foods. Common salt is added to preserve meat and fish, propanoic acid, benzoic acid and their salts are added in bread and cheese as mould and yeast inhibitors. Sulphur dioxide or salts of sulphurous acid are added to preserve dry fruits, jams and jellies. 

Canning of Food for food preservation

 Canning is also a way to preserve food for longer time. Now-a-days foods to be canned are placed in thermally sealed containers and then heat processed. Severe heat treatment destroys the spores of harmful organisms present in food.

 Method of the Preservation of Fruits and Vegetables 

 Before packing the vegetables and fruits in the boxes, they are peeled, boiled and dried. Mixing of common salt preserves the dried vegetables for a longer period of time. 

How to makeTomato Ketchup 

 For the preparation of “Tomato Ketchup” tomatoes are boiled, peeled and then passed through the sieves to separate the seeds and the resultant juice is concentrated by heating. For each kilogram of tomato juice, 1/4 kilogram of sugar is added. It is cooked for few minutes and then salt, chillies and spices are added according to the taste. At the end, add 0.1% sodium metabisulphate and mix it thoroughly. 

Peservation of of Jam and Jelly

 The preservation of fruit in the form of jams, jellies and marmalades is an older method than canning and freezing. Many fruits contain enough pectin to make a gel product. When sugar and acids are added to the fruits in right proportion and heat is applied, the fruits can be preserved without sterilization which is necessary in canning.

Preservation of Food by Irradiation 

 Gamma rays have a high preservation power. If foodstuffs are irradiated by a beam of gamma rays, bacteria that may be present are killed. In the absence of bacteria, the food will not be spoiled for a long time especially if it is stored in air tight containers.