Causes and Sources of Food Contamination and Poisoning – JSS3 Home Economics Lesson Note (Second Term)

Food contamination is the presence of harmful agents in food, and food poisoning is the illness that follows when contaminated food is eaten.

Behavioural objectives

By the end of the lesson, students should be able to:

1. State the causes of food contamination and food poisoning.
2. Name the major sources of food contamination and poisoning.
3. Name the three types of food contamination.
4. Explain what food spoilage means.
5. List the signs of food spoilage.

What is food contamination?

Food contamination is the presence of harmful substances or organisms in food that make it unsafe to eat.

• Contaminant: any harmful agent in food, such as germs, chemicals or stones.
• Contaminated food: food that has come into contact with a contaminant.
• Food poisoning: illness caused by eating contaminated food.

What are the types of food contamination?

There are three types of food contamination: biological, chemical and physical.

Biological contamination

• Cause: bacteria, viruses, moulds, yeast and parasites in food.
• Example: germs from unwashed hands passing onto cooked rice.

Chemical contamination

• Cause: poisonous chemicals getting into food.
• Examples: insecticide on vegetables, or detergent left on plates and pots.

Physical contamination

• Cause: solid objects found in food.
• Examples: stones in rice or beans, hair, nails, broken glass.

What are the causes of food contamination and poisoning?

The main causes are micro-organisms, parasites, toxins, moulds, yeast, chemicals and allergens.

• Micro-organisms: these include bacteria (Escherichia coli, Salmonella) and viruses (norovirus, rotavirus, sapovirus, etc.).
• Parasites: they take their nourishment from their host, e.g. roundworms and tapeworms.
• Toxins: some bacteria release poisonous chemicals, called exotoxins, outside their cells while they grow and multiply in food.
• Heat and toxins: heating may kill the bacteria, but some toxins survive and can still cause food poisoning.
• Moulds: they grow on stored foods such as bread, maize and groundnuts, and some produce poisonous substances.
• Yeast: it is responsible for the decomposition of food with a high sugar content.
• Chemicals: pesticides, cleaning agents and other poisons that get into food.
• Allergens: a food allergy is an abnormal response to food, triggered by the body’s immune system. The food substance that triggers the response is called an allergen.

What are the signs of food poisoning?

Food poisoning usually shows as stomach and bowel upset within hours or days of eating contaminated food.

• Nausea: a feeling of wanting to vomit.
• Vomiting: the stomach throws out its contents.
• Diarrhoea: frequent, watery stools.
• Stomach pain: cramps in the abdomen.
• Fever: a raised body temperature in some cases.

What are the sources of food contamination and poisoning?

The major sources are air, dust, sewage, rodents, flies, dirty equipment, insects and people.

What is food spoilage?

Food spoilage is the undesirable change that takes place in food and eventually leads to its rejection.

• Another definition: it is the deterioration of the physical and chemical properties of food, making it unfit for consumption.
• Main agents: micro-organisms, enzymes in the food, air, moisture and warm temperature.

What are the signs of food spoilage?

The signs of food spoilage are changes in odour, taste, texture and colour.

Sensory signs of food spoilage

• Unpleasant odour: sour, rotten or strange smell.
• Unpleasant taste: sour or bitter taste in food that should not taste so.
• Unpleasant texture: slimy, sticky or mushy surface.
• Unpleasant colour: fading, darkening or patches of mould.

What is the difference between food contamination, food poisoning and food spoilage?

• Food contamination: harmful agents are present in the food.
• Food poisoning: the illness caused by eating contaminated food.
• Food spoilage: the food changes and becomes unfit to eat.

Evaluation

1. State four causes of food poisoning.
2. Mention five sources of food poisoning and contamination.
3. Name the three types of food contamination.
4. Give two ways in which flies contaminate food.

Assignment

1. Explain what food spoilage means and list four signs of food spoilage.