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Methods Of Food Preservation and Sterilisation (Part I)

By Mumtaz Khalid Ismail

More Links Methods of Food preservations House hold methods of preservation and sterilisation

These days I am receiving a lot of queries about food sterilisation, preservation, and its effects. I hope this article will clear their doubts to some extent regarding this. It is very important to know the proper methods of food preservation not only to store the eatables but also to take adequate precaution to avoid the ill effects of preservatives.

There is no doubt that the fresh food is always better than the preserved food. But it would not be possible as well as practicable to have always fresh food. Food preservation is not a new concept. Right from prehistoric ages man has adopted various techniques for the preservation of food. Techniques used for the preservation of foods attempt to protect food from getting spoiled due to yeast, mould, bacteria, contact with rodents, cockroaches or lizards and contamination with metals such as lead, copper etc.

Methods of food preservation would help to prevent a large amount of food being wasted. Some of the preservation methods not only reduce the nutritive value of foods but causes harmful effect directly.

Preservative methods vary according to the food items and quantity of the items to be preserved. There are household and commercial methods of food preservation available. The principles of food preservation can be broadly classified into two types. They are -

1. Bactericidal method.
2. Bacteriostatic method.

Bactericidal method: In these methods most of the micro-organisms are killed. Examples of bactericidal methods of preservations are cooking, canning, pasteurisation, sterilisation, irradiation etc.

Bacteriostatic method: The principle of this method is prevention of multiplication of micro-organisms. This may be achieved by removal of water, use of acids, oil, or spices and by keeping in low temperature. The commonly used methods of this principle are drying, freezing, pickling, salting, and smoking. A layer of oil on the top of any food prevents growth of micro-organisms such as moulds and yeast's by preventing exposure to air. Spices like pepper and turmeric have little bacteriostatic effect.

Different methods are used for getting rid of micro-organisms and for food preservation.

1. Washing: It is the first level defence. Food items should be washed in clean water to get rid of dirt, micro-organism, helminthic ova or cyst, insecticide etc. Avoid prolonged soaking in water and washing after cutting the vegetables and fruits. Major disadvantage of over washing and soaking is that the water soluble vitamins and minerals will be lost in this process.

2. Cooking: Cooking is the most commonly used food preservative method. This also improves digestibility, taste, flavour, and appearance. If boiling temperature is maintained for a sufficiently long period during cooking will be sufficient to get rid of bacteria and most of the spores. But if low heat is used the spores may survive and at favourable temperature it may germinate releasing bacteria. On re-heating bacteria may get killed but the toxin that produced may survive. This may cause life-threatening diseases.

One of the common example is botulinum toxin. It is commonly associated with vegetables such as peas, corn, green beans and meat and meat products. Disadvantage of cooking is that the over cooking leads to loss of nutrient such as water-soluble vitamins and minerals. Different types of cooking have been practised. They are-

• Boiling and stewing - The disadvantage of this type of cooking is that it leads to loss of nutrients especially water soluble vitamins (B&C) and minerals. This can be limited by using only adequate amount of water for cooking and for required time. The left over water could be used as stock for making soup or other liquid preparations.

  

• Steaming - This is one of the most preferred methods of cooking. By this method nutrient loss in minimal.

• Frying - Do frying only if required. Shallow frying is preferable compared to deep frying. Deep frying at high temperature will produce toxic chemicals such as peroxides, aldehydes, ketones, hydroperoxidases, cyclic monomeres etc. Preferably avoid reusing the fried oil.

• Pressure Cooking - Loss of nutrient is less in this method since only little water is used.

• Baking - Baking is cooking by dry heat. The advantage is that large quantities of food can be cooked. There is not much loss of nutrients and food is easily digestible.

• Grilling - It is one of the ancient methods of cooking. In this method if the food is burnt with coals and fire can cause carcinogenic effect.

• Microwave Cooking - This is the most advanced method of cooking. The disadvantages of microwave cookery are that food is only cooked in small quantities, unattractive, and comparatively expensive for household use. The flavour and nutritive values of vegetables are good in comparison with other methods.
  

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