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Preservation of Food

H4.2: Applies principles of food

preservation to extend the life of

food and maintain safety.

Syllabus Link:

What is Food Preservation?Food Preservation is the process of treating and handling food to stop or slow down food spoilage, thus, allowing the food to last longer.

Unless special methods are used to preserve foods, the the majority of foods are quick to decompose or rot as a result of micro-organisms and enzymes.

Reasons for Preserving FoodsS - Safety

A - Acceptability

A - Availability

N - Nutritive Value

E - Economic Viability

Reasons for Preserving Foods● Safety - Ensures food is safe and free from harmful micro-organisms which can

cause illness.● Acceptability - Keep foods in a state acceptable for the consumer and reduces

wastage.● Nutritive Value - Retain the nutritive value of the food.● Availability - Make perishable foods available all year round which provides for

greater diet variety.● Economic Viability - Achieve economic viability for food producers by reducing

seasonal fluctuations in availability.

Causes of Food Deterioration and Spoilage

Causes of Food Deterioration and Spoilage

M - Microbial Contamination (mould, yeast and bacteria)

E - Enzymatic Activity

E - Environmental Factors (Infestation, oxygen, light and water)

Spoilage of food is caused by one or more of the following factors;

Causes of Food Deterioration and Spoilage1. Microbial Contamination ● Micro-organisms such as; yeasts, viruses, moulds and bacteria cause foods to

spoil.● Example; mould on old bread, sliminess on ageing meat. ● Micro-organisms may be pathogenic, meaning that they have the potential to

make a consumer very ill and, thus, need to be controlled. ● Micro-organisms prefer warm, moist conditions with a neutral pH. When these

conditions are favourable, they begin to multiple.

As micro-organisms grow, they pass through a series of phases.

● PHASE 1 - LAG PHASE

This is the time required for the bacteria to become adjusted to the new environment. The greater the number of micro-organisms present - the shorter the lag time.

● PHASE 2 - LOGARITHMIC PHASE

The bacteria cells grow and multiple because they have adjusted to the environment.

● PHASE 3 - DEATH PHASE

During this phase, the food needed by the bacteria is usually all gone and the bacteria die of starvation.

Especially important in food preservation is the lengthening of the lag phase of micro-organisms as much as possible. This can be accomplished in different ways;

1. Limiting the number of micro-organism will reduce the amount of contamination. The fewer micro-organisms present - the longer the lag time. This can be achieved by avoiding unclean containers, equipment, or utensils used in food preparation.

2. The micro-organisms will take longer to begin multiplying in an unfavourable environment. Such an environment can be produced by changing the moisture, temperature or pH level.

3. Putting the food through processes such as heating to high temperatures or irradiation actually damages the micro-organisms

The time it takes for a single cell to divide and grow into two new cells is called the Generation Time. The time shortens as the conditions become favourable. For example; if the food is chilled, the generation time will lengthen

If the conditions for growth are good, a single bacterium can reproduce every 20 minutes.

● The spoilage of food caused by micro-organisms will be prevented only if all the spoilage organisms are killed (or removed) and re - contamination is prevented

● Stopping the multiplication of micro-organisms does not necessarily prevent the decomposition of a food. For example; freezing - micro-organisms remain dormant.

● Minimising cross-contamination is crucial as it ensures that food remains safe. Cross-contamination is the transfer of microbes to food via other items.

● All foods spoil, however, some spoil faster than others. Perishable foods spoil faster than other foods and are more likely to cause food poisoning.

● Chemical Preservatives used to remove micro-organisms

Causes of Food Deterioration and Spoilage2. Enzymatic Activity:

● An enzyme is a substance produced by a living organism. Enzymes are found in meat, fruits and vegetables.

● Enzymes do not affect the safety of the food if consumed. ● Enzymes cause fruits and vegetables to over-ripen once harvested and results in

loss of turgor due to tissue decomposition.

Causes of Food Deterioration and Spoilage3. Environmental Factors:

● Organisms such as insects and rodents can cause spoilage of food, such as weevils in flour and rodents transmitting bacteria.

● Washing may be dangerous if the water is contaminated and adds spoilage organisms.

● Exposure to oxygen can also encourage microbial growth and speed up enzymatic browning.

Principles behind Food Preservation

Techniques

Principles behind Food Preservation Techniques

Principles behind Food Preservation TechniquesT - Temperature Control

R - Restriction of Moisture

E - Exclusion of Air

P - pH

1. Temperature Control

● Cooking a food by heating is the simplest and most commonly used method of food preservation.

As food is cooked, two important events occur;

- Enzymic reaction rates begin to slow.

- Micro-organisms are killed when temperatures reach above 60 degrees celsius.

-

● Temperatures above 100 degrees celsius destroys all enzymes and micro-organisms. However, some

spore-forming micro-organisms, such as; Clostridium Botulinum can survive at 100 degrees celsius for

up to 5 hours.

● In addition, the higher the acidity of a particular food is, the less time and the lower the temperature it

will take to kill any bacteria present.

● Cooling of the food after cooking is also another important factor in preventing the growth of bacteria. If

the food is not eaten hot and is allowed to cool slowly, it can make a person ill.

● Processes which remove moisture from food, such as dehydration and evaporation, are effective

in preventing the actions of both enzymes and micro-organisms. This is because both enzymes

and micro-organisms need clean, liquid water to survive.

● Enzymes can still be active in freezing conditions, but their activity occurs very slowly - this is

the reason why foods cannot be stored in the freezer indefinitely.

2. Restriction of Moisture

● Most microbes require oxygen to be active. By removing air from around the food, the

environment becomes unfavourable and microbes become dormant.

● Some bacteria are anaerobic and care must be taken with processing and packaging options as

food poisoning may result.

● Manufacturers exclude air from packaging such as cans and bottles through a process known as

‘vacuum packing’. This is a process in which the air in the headspace is removed and a vacuum is

put in its place.

3. Exclusion of Air

● Adding acids to foods can minimise spoilage by denaturing enzymes and destroying micro-

organisms.

● Additives, in the form of chemical preservatives, food acids and smoke can be used to destroy

micro-organisms.

● Tomato salsa, jam and pickles are a few of the foods eaten daily that use chemicals to inhibit

microbial growth.

4. pH

1. Many manufactured food producers apply a variety of the principles of preservation to ensure the stable shelf-life of their products. Suggest which principles of preservation are being used when the following foods are manufactured.

a) Bottled Jam

b) Bacon and Salami

c) Pasteurised Milk

d) Beef Jerky

e) Canned Fruit