Microorganisms & Enzymes (AQA GCSE Food Preparation & Nutrition)

Microorganisms, enzymes & food

• Food spoilage can be defined as:

Loss of food quality that causes food to become inedible

• Food spoilage can occur due to:

  • activity of microorganisms

  • enzyme activity within the food

Microorganisms and food spoilage

• Microorganisms are very small organisms that can only be seen using a microscope, e.g.

  • bacteria

  • fungi, such as yeast and mould

• Not all microorganisms are harmful, but some can cause food spoilage and may result in food poisoning if consumed

Conditions for microorganism growth

• In order to grow, microorganisms need specific conditions, including:

  • correct temperature

    • Conditions need to be warm enough for microorganisms to survive without being hot enough to destroy them

  • water

    • Moisture needs to be present in the food or in the surrounding air

  • food

    • Microorganisms need nutrients to enable them to survive and reproduce

  • correct pH

    • Most microorganisms cannot survive in highly acidic or highly alkaline conditions

• In order to reach harmful levels, microorganisms need a sufficient length of time under suitable conditions

Preventing microorganism growth

• Microorganism growth can be reduced by making the conditions inhospitable; this can be achieved by:

  • reducing the temperature, e.g. by putting food in the fridge or freezer

  • increasing the temperature by cooking food

  • reducing the length of time for which food is left at room temperature

  • providing an acidic environment, e.g. by pickling

  • removing water, e.g. by drying, salting or adding lots of sugar

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High risk foods for microorganism growth

• Foods that spoil easily due to microorganism growth are known as high risk foods

  • These foods provide an environment that aids the growth of microorganisms; they are often

    • moist

    • high in protein, which provides food for microorganisms

  • High risk foods are generally 'ready-to-eat', meaning that they will not undergo a further heating process before consumption that might destroy microorganisms

• Examples of high risk foods include:

  • cooked meat and fish

  • dairy products, such as cheese and milk

  • some forms of egg, and foods that contain egg, e.g. mayonnaise

  • precooked shellfish, e.g. mussels and prawns

  • meat products, including gravy, stock and sauces

  • cooked rice

Enzymes and food spoilage

• Enzymes are biological catalysts made of protein

• The activity of enzymes that are already present inside foods can lead to enzymic browning

• Food spoilage due to enzymes can be prevented by denaturing enzymes to reduce their activity; this can be achieved by:

  • heating, e.g. by blanching vegetables in boiling water for a few minutes before freezing

  • adding an acid, e.g. putting lemon juice on sliced apple