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Food Decay and Preservation

Bacteria and fungi are the main groups of decomposer organisms. In this lesson let’s discuss how these microorganisms involve in food decay. Food decay is also known as food spoilage. Also, you can learn about a list of ways of food preservation in order to avoid food spoilage.


What are the factors needed by bacteria and fungi to grow?


1) Food

2) Warmth

3) Moisture


What is the factor which is needed by plants and not needed by bacteria and fungus?



E.g. If you leave moist food in a cupboard and forget about them, they will go bad.

Examples of food spoilage


How do bacteria and fungus involve in food decay or food spoilage?


The tiny spores (tiny reproductive cells in bacteria and fungus) of bacteria and fungi land on the foods from the air. As they grow, the bacteria and fungi produce chemicals that allow them to dissolve the foods. These chemicals can make us ill. Then we are said to have food poisoning.


Example of Food Spoilage - Mouldy Bread

Example of Food Spoilage – Mouldy Bread


Food Preservation (Preserving food)


What is meant by food preservation or preserving food?


Several ways to stop or slow down the decay of foods


Examples of food preservation


Following is the list of food preservation methods;


a) Freezing

b) Drying

c) Chemical preservatives

d) Canning and bottling



Bacteria and fungi need warmth to grow. In low temperatures they stop growing.


Examples of food preserved by freezing


Following is the list of food preserved by freezing;


1)    Meat

2)    Fish

3)    Fruits

4)    Vegetables

5)    Fresh foods

6)    Cooked foods



Bacteria and fungi need moisture to grow. They cannot grow in dried foods which are stored in sealed containers.


Examples of food preserved by drying


Following is the list of food preserved by drying;


1)    Vegetables

2)    Fruits

3)    Soup

4)    Milk

5)    Cereal

6)    Fish

7)    Lentils

8)    Chick peas

9)    Beans


Chemical preservatives

Safe chemicals can be added to food to stop the bacteria and fungi from feeding and growing.


Examples of chemical food preservation


Following is the list of examples of chemical food preservation;


E.g. – 1) A lot of sugar is added to fruit to make jam and marmalade.

          2) Vinegar, used in pickles, is too acid for bacteria and fungi to be able to grow.

          3) A lot of salt is added when bacon is produced. 


Canning and bottling


Why will canned and bottled food last for many months or even years?


1) Some foods like fruits and vegetables are heated strongly to destroy or kill any germs such as bacteria and fungi.

2) Then the foods are sealed in airtight containers.

3) So that no more bacteria and fungi can get into the food until the can is opened.


Taking care


It is important to be careful when we handle stored or preserved food. The surface where we prepare food need to be very clean, or bacteria will spread to the foods we eat and may make us ill.


How fast can bacteria grow?


A bacterium can divide into two new bacteria in minutes.


List of places where bacteria can stay


1) In our nose

2) In our throats

3) In our cuts and sores

4) On our skin

5) On our hands


List of animals that can pass bacteria on to the food


1) Mice

2) Rats

3) Flies


Flies can pass bacteria on food

Flies can pass
bacteria on food

Rats can pass bacteria on food

Rats can pass
bacteria on food


Try this activity on harmful and useful microorganisms.