OCR AS Biology - Microorgasims and Food

Clear notes on Microorganisms and Food - based on OCR syllabus.

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Microorganisms and food
Preventing food spoilage
COOKING The heat denatures the enzymes and other
Kills the microorganisms
PASTURISING Heating to 72C for 15 seconds
Cooling rapidly to 4C, killing harmful
DRYING, SALTING, COATING IN Dehydrate any microorganisms
SUGAR As water leaves them by osmosis
SMOKING Food develops a hardened, dry outer surface
Smoke contains anti-bacterial chemicals
PICKLING Uses an acid pH to kill microorganisms
by denaturing their enzyme sand other proteins
IRRADIATION Ionisation radiation kills the microorganisms
By disrupting their DNA structure
COOLING & FREEZING Do not kill microorganisms
But delay enzyme activity so their metabolism,
growth and reproductively is slow.
Preventing further contamination
CANNING ­ the food is heated and sealed in airtight cans
VACCUUM WRAPPING ­ air is excluded so microbes cannot respire aerobically
Any plastic or paper PACKAGING

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Microorganisms and food
Using microorganisms to make food
Is milk affected by Lactobacillus bacteria
The Lactobacillus uses the lactose sugar in milk lactic acid = causes the milk protein to
Yoghurt can help to ensure that our digestive system contains the non-pathogenic bacteria it
needs to aid digestion
Is made from milk that has curdled
Curds is acted upon by Lactobacillus bacteria
For additional flavour chees is contaminated with Penicillium
Rises by yeast
Yeast anaerobically respires to release Carbon dioxide
Bubbles…read more

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Microorganisms and food
How do microorganisms cause food to spoil?
Microorganisms can start to digest food
Things happen externally and the food may begin to smell sweet
This is the smell of sugars released from polysaccharides.
Other organisms may release their waste products into food, these may act as a toxin.
Visible presence of fungi or bacterial colonies on our food is also considered spoilage.…read more


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