Fruit & Vegetables (AQA GCSE Food Preparation & Nutrition)

Cooking with fruit & vegetables

• When preparing fruits and vegetables it is important to consider processes that may reduce food quality or nutritional value; such process include:

  • enzymic browning

  • oxidation

Enzymic browning

• Fruits and vegetables may turn brown when cut surfaces come into contact with oxygen in the air; this process is sped up by enzymes, and so it is known as enzymic browning

  • Enzymes are proteins found within living organisms that act as biological catalysts

  • Biological catalysts speed up the rate of chemical reactions in living organisms

Alexas_fotos, via pixabay

• Enzymic browning can be slowed down by reducing the activity of enzymes within the food; this can be achieved by:

  • blanching

    • Fruit or vegetables are boiled in water for a short period

    • The high temperature causes the enzymes to denature, reducing the rate at which browning occurs

    • Blanching is often used to prepare fruit or vegetables for freezing

      • Note that freezing alone will slow down enzyme activity, but blanching will destroy enzymes so has a greater effect

  • application of acid

    • Adding an acid to a fruit or vegetable will also cause enzymes to denature, e.g. adding lemon juice to sliced apple

Loss of vitamins by oxidation

• Oxidation is the loss of water soluble vitamins when fruits or vegetables are exposed to the air, or to heat

  • Examples of water soluble vitamins include:

    • B vitamins

    • vitamin C

• The longer a fruit or vegetable is exposed to the air, the more vitamins will be lost, so reducing exposure time helps to reduce oxidation; this can be achieved by:

  • minimising the time between cutting and cooking fruits and vegetables

  • boiling the water before cooking and using a pan lid to reduce cooking time

  • not overcooking fruits and vegetables

  • serving cooked fruit and vegetables immediately after cooking