• Microorganisms?can be used by humans to produce foods and other useful substances
• As well as fungi (e.g. yeast used to make bread),?bacteria?are also used in the production of certain foods
• Bacteria are useful because they are?capable of producing complex molecules?(e.g. certain bacteria added to milk produce enzymes that turn the milk into yoghurt)
• They are also useful because they?reproduce rapidly, meaning the amount of chemicals they can produce can also rapidly increase

Using bacteria to make yoghurt

• Yoghurt is made in a process that relies on the presence of a specific type of bacterium – in this case,?Lactobacillus
• First, all equipment is?sterilised?to kill other, unwanted bacteria and to prevent chemical contamination
• Milk is then?pasteurised?(heated)?at 85-95°C?to kill other, unwanted bacteria
  • Contamination with other bacteria could?slow production of the yoghurt?by?competing?with the?Lactobacillus?for the lactose in the milk
  • It could also?spoil the taste?of the yoghurt

   

• The milk is then?cooled?to?40-45°C?and?Lactobacillus?bacteria is added?
• The mixture is?incubated?at this temperature for several hours, while the?Lactobacillus?bacteria?digest milk proteins?and?ferment (digest)?the sugar?(i.e. the?lactose) in the milk
• The?Lactobacillus?bacteria?convert the lactose into lactic acid?and?this increased acidity?sours and thickens the milk?to form?yoghurt
  • This lowering of the pH also helps to prevent the growth of other microorganisms that may be harmful, so acts as a preservative
  • This means the yoghurt can be kept for a longer time (compared to fresh milk)

   

• The yoghurt is then stirred and?cooled to 5°C?to?halt the action of the?Lactobacillus?bacteria
• Flavourings, colourants and fruit may be added before packaging

Industrial fermentation

• Fermenters?are containers used to grow (‘culture’) microorganisms like bacteria and fungi in?large amounts
• These can then be used for?brewing beer, making yoghurt?and?mycoprotein?and other processes not involving food, like producing?genetically modified bacteria?and?moulds that produce antibiotics?(e.g. penicillin)
• The advantage of using a fermenter is that?conditions can be carefully controlled?to produce large quantities of exactly the right type of microorganism

A diagram of an industrial fermenter used to produce large quantities of microorganisms

Controlling Conditions in an Industrial Fermenter Table

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