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Food Preservation - Homescience Form 4

Food Preservation


This is the process of treating food to stop or slow down food decay and deterioration.











Causes of Food Decay

Food spoilage and decay is brought about by:

  • Bacteria
  • Fungi
  • Enzymes
  • Oxidation

Objectives


By the end of the lesson, you should be able to:
i) Define food preservation
ii) Identify the agents of food decay and spoilage

Bacteria

These are single celled micro-organisms that multiply rapidly under warm and moist conditions.


Fungi

These include the yeasts and moulds. They thrive under warm, moist conditions.


Enzymes

They are organic catalysts that speed up rate of reaction. They are responsible for the ripening of fruits and decay of fruits, vegetables and meat.

Oxidation

This is a reaction in which oxygen is added to a substance. This brings about change especially in colour.

Objectives


By the end of the lesson, you should be able to:
i) Classify methods of food preservation
ii) Describe the methods used in food preservation

Traditional Methods



Salting


This is the use of high concentration of salt which draws water from the food. This makes the conditions unfavourable for the thriving of micro-organisms.

Salted Meat

Smoking


This is a method of using smoke from burning firewood. The food is placed on a rack above the fireplace. The heat partly dries the food and the smoke coats it providing a protective layer. Examples of food which is smoked include fish, meat and maize on the cob.


Smoking Fish

Sun Drying


Drying removes moisture from food, hence depriving micro-organisms the moisture required for survival. The food is spread on a surface under direct sunshine and is occasionally turned for complete drying e.g. grains, omena/ dagaa, meat, and some tubers.



Sun drying fish

Fermentation


This is the process of using yeast or healthy bacteria. Yeast ferments to produce alcohol while the healthy bacteria for example in milk chage the lactose into lactic acid, making the conditions unsuitable for the harmful micro-organisms. Examples of food which are fermented are porridge and milk.


Fermented porridge

Modern methods

Refrigeration and Freezing

This involves the use of low temperatures which slow down or inactivated the action of micro-organisms. In refrigeration the food is chilled while in freezing, there is formation of ice which solidifies the food.

Canning and Bottling

The food to be canned/ bottled is heated to kill micro-organisms and drive out air out of the jar/can. The food is then sealed and a vacuum is created as it cools. The vacuum prevents the re-entry of air, which may contain micro-organisms.

Pasteurization

This is the process of heating food e.g. milk to a specific high temperature for a definite length of time (in seconds). It is then cooled immediately for storage. The high temperature destroy the micro-organisms.

Use of Additives

These are either natural or chemical substances added to food to destroy or inhibit the action of micro-organisms. They include,
sugar, v
inegar, b
enzoic acid, s
ulphur dioxide and c
arbon IV oxide.


Irradiation

This is the exposure of food to gamma rays radiation. The treatment kills moulds, bacteria and insects. It also reduces the ripening and spoilage of fruits. Some of foods that are irradicated spices and condiments.

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