OCR AS Biology- Microorganisms

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  • Created on: 25-03-13 21:55
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When food is created using microorganisms, there needs to be controlled conditions
otherwise food will be spoiled as microorganisms will grow etc.
There are six types of treatment that you need to know about that affect microorganisms:
Adding sugar
Adding salt
Heat treatment
Methods to prevent further contamination include:
- Canning- the food is heated and sealed in airtight cans
-Vacuum wrapping- air is excluded so microbes cannot respire aerobically
-any plastic or paper packaging
Some foods can be freeze dried, e.g. fruits, and this is done via putting the food
into a vacuum, and this keeps food below minus eighteen degrees Celsius.
The food doesn't freeze, the low pressure surrounding the food items turn into
water vapour.
This does less damage as ice could pierce and break cell membranes.
Salting is traditionally used for meat, fish and some kinds of vegetables.
Salt may be rubbed into the food or the food is submerged into a low potential
This interferes with the microorganism's ability to absorb water (which they need
to survive).
Enzymes and other proteins may denature if placed in an acidic solution.
Vinegar (an alkali) is often used for products such as pickles and they keep the
food at its original condition.
Microorganisms are killed by extreme heats; some heat-resistant pores can survive
above 100 degrees.
Pasteurised milk is an example, it doesn't kill all of the bacteria (heats up to 65
degrees and then cools down to 20 degrees), and this is why milk can be stored
for five days.
UHT (Ultra High Temperature) milk kills all bacteria as the milk is boiled and stored
in a container.

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It is made by mixing yeast, sugar, flour and water into a dough. The yeast turns the sugar
into ethanol and carbon dioxide.
This is made by adding yeast to grape juice. The yeast turns the sugar in the grape juice
into ethanol and carbon dioxide.
This is made by adding bacteria to milk. The bacterium turns the sugar in the milk to lactic
acid causing the milk to clot and thicken into yoghurt.…read more

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