OCR F212 2.2.4

Microorgansims have been used for many years in the manufacture of food, eg:

• Yoghurt is milk that has been affected by the Lactobacillus bacteria. The Lactobacillus uses the lactose sugar in milk to make lactic acid, which causes the milk protein to thicken. The bacteria partially digests the milk, making it easier for humans to digest. Yoghurt helps ensure that our digestive system contains the non-pathogenic bacteria it needs to aid digestion.
• Cheese is made from milk that has curdled. The solid portion of the milk is acted upon by Lactobacillus, the cheese can be given additional flavour by contamination with fungi such as Penicillium to produce 'blue' cheese.
• Bread is made to rise by yeast, which respires anaerobically to release carbon dioxide. The bubbles of gas collect in the dough causing it to rise.
• Alchohol is another product of anaerobic respiration of yeast. Cereal grains containing the sugar maltose can be used to brew beer, as the yeast respires the sugar. Grapes contain the sugars fructose and glucose, which the yeast uses in maikng wine.

Recently microorganisms have been used to manufacture protein that is used directly as food. This protein is known as single-cell protein (SCP). The best known protein made by microorganisms is Quorn, a mycoprotein - a protein made by fungus. Quorn is marketed as a meat substitue, it is also healthy for non-vegetarians as it contains non animal fat or cholesterol.

There is huge potential in SCP production using microorganisms like