Biology- micro-organisms and food

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Microorganisms and food spoilage:

Many microorganisms obtain their nutrition by digesting organic matter around them. In doing so, they leave behind waste products. The organic matter they digest might well be our food. Once the effects of their activities are noticeable, we consider the food to be spoilt.

There are four main ways that microorganisms can spoil our food:

·         Visible growth of microorganisms on food. This is most obvious when fungi grow on food. For example, colonies of the moulds MUCOR and PENICILLIUM often grow on bread. The mould had usually been growing for a few days before it becomes noticeable as either black (MUCOR) or blue/green (PENICILLIUM) mould.

·         Microorganisms use external digestion processes. They release enzymes into the food and absorb the nutrients relapsed by the breakdown of the food molecules. When this happens, food often smells sweet as sugars are released from carbohydrate molecules. The food will eventually be reduced to mush by the action of enzymes.

·         The bacterium CLOSTRIDIUM BOTULINUM produces a toxin called botulinum. This causes botulism. If these bacteria are growing on food, the toxin will be present. It is one of the most toxic substances known - as little as 1 microgram can kill a person.

·         The presence of microorganisms in food can cause infection. For example SALMONELLA bacteria, sometimes present in poultry products, attack the lining of the stomach and digestive system.


How do we prevent food spoilage?

We can prevent food spoilage by using. Food quickly, while it is still fresh. If food is to be kept for longer, it must be treated to prevent spoilage. This can be done by either killing any microbes already on the food, or preventing them from reproducing. The food must then be packaged to prevent further contamination with microbes.

Treatment methods to kill microorganisms or prevent their reproduction include:

·         cooking- the heat denatures enzymes and other proteins and kills microorganisms

·         pasteurising- this involves heating to 72°c for 15 seconds and then cooling rapidly to 4°c, killing harmful microorganisms

·         drying, salting and coating in sugar-these processes dehydrate any microorganisms as water leaves by osmosis

·         smoking- the food develops a hardened, dry outer surface,, and smoke contains antibacterial chemicals

·         pickling- this uses and acid pH to kill microorganisms by denaturing their enzymes and other proteins

·         irradiation- ionising radiation kills the microorganisms by disrupting their DNA structure

·         Cooling and freezing- these do


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