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Food Biotechnology
Techniques to prevent
food spoilage
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p g
Micro-organism Growth
Reminder that optimal conditionsfor micro-organism growth are:
- warm (usually !-"#o$%
- good food supply- moist
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&ow can we preventfood going 'ad
To some e)tent we can stop or delay thespoilage of food*
Mainly this is done 'y stoppingdecomposers or micro'es getting to the
food or changing the conditions to slow oreliminate micro'e growth*
This is the 'asis of food preservation*
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&ow can we preventfood going 'ad
There are four main ways to preserve food:
Cold treatment:eg deep free+e, refrigeration*
Drying: eg dehydration
Heat treatment:eg sterilisation, &T (ultra
heat treatment%, 'ottling, canning,pasteurisation*
Chemical treatment:eg pic.ling, smo.ing,salting
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$old Treatment
Free+ing does not kill microbes, 'ut itstops them from multiplying and slowstheir action/ the colder it is the slowerthey get*
0s soon as the food thaws the micro'es(previously dormant% start up again andfood 'egins to go 'ad*
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Free+ing
Meat decays particularly quic.ly 'ecause thefree+ing process 'rea.s open the cells and themicro'es can invade quic.er*
1epending on the type of food and the free+ingtemperature food can 'e stored for up to a year*
Most free+ers operate at -2o$ or -34o$
Free+ing food is important these days fortransporting*
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Refrigeration
Refrigerating operates at 5ust a'ove free+ingtemperature*
6t slows 'acterial action down 'ut does notstop it*
Therefore food can only 'e stored in the fridge
for a few days*
Food should 'e defrosted in the fridge* Theoutside defrost 7rst, allowing 'acteria tomultiply while the inner part of the foodcontinues to defrost*
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Refrigeration
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1rying
Micro'es need moisture 8 they go
dormant in 'ad conditions*
9ven if spores land on dried foods
they cannot germinate if there is notmoisture*
1ried food lasts inde7nitely*
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1rytorage
$ommon methods
include Evaporation
Dehydration
Adding salt
Adding sugar
Freezing
Freeze drying
Jam
Anchovies
Water notaccessible
Milk
Fruit
Reducing the water helps toeliminate a avourable
environment or bacteria tomultiply!
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Removing moisture from food is called dehydration
sually it is done 'y having hot air 'lown over it*
Mil., eggs, potato, 7sh can all 'e dehydrated/ assoon as you add water it can 'e eaten*
1ehydrated foods are compact and light and can 'eeasily transported eg space travel, camping etc*
;nce water is added it can go 'ad in the usual wayas micro'es 'ecomes active again
1ehydration
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1ehydration
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&eatTreatment
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Bottling
Fruit can 'epreserved 'y 'ottling*
0 special 5ar with a lidand ru''er rim isused*
The 5ar is 7lled withfruit and syrup*
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Bottling
The 5ar is then heated and allowed to cool*
0s it cools the air inside shrin.s and itcreates a vacuum*
The lid pulls on tightly = the ru''er ringma.es it airtight*
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$anning
Food is place in metalcans
The air is suc.ed out ofthe cans and they arethen sealed
The cans are thenheated under pressureuntil all the micro'es
are .illed*
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ltra &eat Treatment(&T%
&eat is used to .ill 'acteria in mil.
Mil. is heated to a very hightemperature and then it is sealed*
6t can alter the >avor so most peopleprefer pasteurised mil.*
&T mil. can last quite a long time*
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?asteurisation
?asteurisation is named after @ouis ?asteur
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?asteurisation
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$hemical Treatment
0dd a chemical to the food which
.ills 'acteria 'ut is harmless toman*
6ncludes/
- pic.ling- smo.ing- salting
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?ic.ling
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mo.ing
The food is heldover a wood 7re
The smo.econtainssu'stances which
.ill 'acteria aswell as giving thefood a delicious>avor*
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alting
The food is either soa.ed in salt 'rine or salt is ru''edinto it
The salt draws the watermoisture out of the 'acterialcells using osmosis, hence .illing them*
6n hot countries, local people often put fruit or 7sh out inthe sun*
This dries the food and reduces the moisture content andleaves a high concentration of sugar or salt*
This .ills any micro'es present and this is why dried fruitlasts so long*
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alting
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?reservatives
0 speci7c category of food additives*
?rotect consumers when using multi-usecontainers
Concentrated tomato paste
Examples include; salt, sugar, sulphur dioxide,
smoke
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Reduced ;)ygen
Many microorganisms require o)ygen tosurvive*
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Food 6rradiation
@ast resort if no other method of preservationavaila'le*
Food is not radioactive*
6t destroys 'acteria* #arasites& moulds and yeast that spoil ood!
+almonella!
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Food 6rradiation
6s used to
,reat herbs and spices
(nwanted pest in traded ood
Carying doses are used
-ow dose destroys moulds
'igh doses kill bacteria that causeood poisoning
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