Food Preservation

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ENZYMES:

They are chemical catalysts found in all cells.

they break animal and plant tissue causing:

Fruit to ripen

meat to tenderise

oxidation

However if the enzymes continue to work food is spoiled.

OXIDATION OR ENZYMIC BROWNING:

Oxidation is when the flesh of fruit turns brown. It can be prevented by:

Adding acid (like lemon juice)

blanching (boiling water destroys enzymes)

Contact with air prevented (good old clingfilm!)

MICROORGANISMS:

Yeasts: Single celled organisms that are found naturally on the skin of fruits and in the air. They're also grown commercially and sold.

USEFUL: make a variety of products: bread, beer and wine.

NON-USEFUL: Can spoil fruits and jams. The food would have an altered taste.

Bacteria: Single celled organisms which are everywhere, even though they cannot be seen,

USEFUL: Needed in the food industry, mainly in the production of yoghurt

HARMFUL: bacteria which causes food poisoning.

Moulds: Fungi which grows from 'spores' found in the air. They settle on food products and multiply. When they're visible the food is describe as being 'mouldy'.

USEFUL: Deliberately used in the food industry, used in quorn and cheese.

HARMFUL: cause food spoilage

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FOOD POISONING

Staphylococcus Aureus: Found due to food handlers poor hygiene

Bacillus Cereus: Found in cooked rice, lentils and beans.

E-Coli: Found in raw meat.

Listeria Monocytogenes: Found in soft cheeses and incorrectly heated cook-chill meals, also meat which is no cooked through and in unpateurised milk

Salmonella: found in poultry and eggs

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CROSS CONTAMINATION

It occurs when:

raw food touches high risk foods

liquid or juices from raw foods drip onto another.

bacteria are carried from one food to another by hands, knifes, chopping boards or dirty cloths.

The symptoms of food poisoning include: diarrhoea Vomiting stomach cramps fever headaches.

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Conditions for Bacteria growth:

TIME: bacteria is able to multiply

TEMPERATURE: bacteria grows best at 37oc. however they produce quickly at any temperature between 5oc and 62oc

MOISTURE: They like these condition and most foods naturally have these conditions

PH LEVEL: bacteria grows best in neutral PH

OXYGEN: Some bacteria (not all) require oxygen to reproduce.

HIGH RISK FOODS:

Raw or cooked meat

raw or cooked fish

egg products

cooked rice and lentils

gravies and soups

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PRESERVATION METHODS.

M.A.P and removal of air

removing air and sealing bacteria means bacteria is not able to grow.

Removal of moisture

all micro-organisms need moisture, and without it they can't survive.

Additives

Chemical preservatives destroy bacteria and prevent them reproducing.

Irradiation

bacteria is destroyed, but it has limited use in the UK

Reducing Heat

bacteria are unable to grow in low temperatures. they reproduce at a slower rate until they become dormant (hibernating) they come back to life after defrosting.

Application of Heat

Micro-organisms are destroyed at high temperatures.

Methods of Extending the shelf-life of foods are by lowering the temperature are: Chilling, cook-chill, freezing and AFD

Cold temperatures slow down the speed that bacteria reproduces but does not destroy it.

very low temperature cause bacteria to be formant or inactive

However as the food warms up, the bacteria begins to reproduce again.

CHILLING

Food is kept in good condition for a short period of time

chilled foods are stored between 1oc and 8oc.

the optinum chilling temperature is 4oc as it prevents the growth of listeria monocytogenes

chilling causes enzyme activity to be reduced

COOK-CHILLING

Prepared dishes are cooked and them cooled between 0oc and 9oc

food is stored in a refridgerator at a temperature between 0oc and 3oc

they have a shelf life of 5 days, including the day they were made.

they have to be heated to at least 72oc before being eaten

they should be eaten within two hours and left overs thrown away

they shouldnt be re-heated

FREEZING

commercially frozen food can be quick frozen.

quick freezing reduces cell damage in the food

it is then stored in the freezer between -18oc and -29oc

there is a high demand for frozen food.

ACCELERATED FREEZE DRYING (AFD)

its a combination of freezing and drying

food is quick frozen then placed ina vacuum.

on heating the food is left dry

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HIGH TEMPERATURE METHODS:

pasteurisation

sterilisation

ultra heat resistant

canning

irradiation

Pasteurisation:

Liquid is heated and held at a high temperature for a short time

The temperature and time vary on the liquid being heated

pasteurisation is a short time preservation

it only kills some bacteria

Sterilisation:

Food is heated to high temperatures

in high temperatures and held for a long time caramelisation occurs

this changes the flavour of the product

it destroys most bacteria

it is used in a wide variety of food

Ultra heat-treatment (UHT)

Liquid is heated to high temperatures for a short period of time

it is a long term method of preservation

it causes no change to the flavour of the product

it kills bacteria

Canning

it is a form of sterilisation

Food can be packed in cans or bottles or pakced into aseptic containers

the containers are sealed to prevent re-contaminatiob

Irradiation

uses ionising radiation from electron beams or gamma rays

the food absorbs energy allowing radicals to develop

radicals destroy bacteria

this is a new form of processing into the Uk

NOT THE SAME AS RADIATION

ADDITIVES

The ingredients by law must be added in descending weight order

The 'E' number is a code used instead of chemical names which are long and complicated

Colours (E100s)

Give colour to food

Preservatives (E200s)

Keep food safe to eat for longer by stopping the growth of bacteria

Emulsifiers and Stablisers (E400s)

Prevent emulsions seperating

Antitoxidants (E300s)

Prevent fats going rancid through oxidation. they help slow down the browning of fruit.

Commonly used additives:

Sweeteners

flavourings

flavour enhancers

thickening/gelling agents

PRESERVATION

EXTENDING SHELFLIFE

ADDITIVES