1.0 WHAT IS FOOD PRESERVATION?

The dictionary meaning of the word “preserve” is to keep safe, retain

quality, prevent decomposition or fermentation. When we apply this

meaning to food preservation it can be defined as “A process by which

certain foods like fruits and vegetables are prevented from getting spoilt for

a long period of time. The colour, taste and nutritive value of the food is also

preserved.”

The definition of food preservation states that the preserved food should

retain their colour and taste. This means that the colour and taste of food

which is present at the time of preservation should not change. Let us take

the example of preserving grapes as raisins. Raisins are prepared by sun

drying grapes. During the drying process the grapes change colour from

green to brown, and taste, sweeter. However, once they are dried and stored,

they do not change colour or taste. Like colour and taste, a well preserved

food should not change texture.

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2.0 WHY DO WE NEED TO PRESERVE FOOD?

Now that you have understood the definition of food preservation, did you

think about why we should preserve foods? Can you think of a few reasons

for preserving foods?

One of the important reasons for preserving foods is to take care of the

excess produce. The second reason for preserving foods is that they add

variety to our meals. The third reason is it helps reaches areas where the

food item is not grown. Availability of some preserved foods can add to the

variety and nutritive value of meals. For example inclusion of dehydrated

peas, green leafy vegetables or canned fruits in the meals is a good idea in

such areas. Another reason is it makes transportation and storage of foods

easier. Preservation of foods usually reduces bulk. This makes their

transportation and storage easier since it requires less space.

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3.0 WHY DOES FOOD GETS SPOILT?

The definition of food preservation states that preservation is keeping food

in such a state that they do not get spoilt for a long period. Before we look at

the reasons of food spoilage, let us understand when a food is spoilt. When

you keep bread outside the refrigerator for few days, a spongy growth is

seen on it, which may be white, green on black in colour. The bread thus

gets spoilt due to growth of mold and becomes unfit for consumption.

Likewise, if cooked dal or vegetables is left outside for some time, it

develops a bad smell and bubbles due to fermentation. The dal and

vegetables are thus spoilt and cannot be eaten. Can you now say when is a

food spoilt?

Food is said to be spoilt if there is rotting i.e., bad smell, fermentation

example, bubbles/gas in the food or mold example, spongy growth on the

food stuff. Formation of soft spots or soft brown spots on fruits and

vegetables is also food spoilage.

Why do foods get spoilt? Foods get spoilt mainly due to the presence of

micro organisms like bacteria, yeast,and fungi, enzymes (present in foods),

oxidation of fats in food, insects, worms, and rats.

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4.0 METHODS OF FOOD PRESERVATION

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Smoking

Boiling

Pasteurization

Waxing

Freezing

Cooling

Vacuum Pack

Salting

DryingPickling

Bottling & Canning

FOOD PRESERVATION

METHODS

Salting

1. Food can also be preserved with salt. This process is called salting.

2. Salting can be done in two ways as shown below.

a) Adding a lot of salt to the food.

b) Soaking the food in a salt solution.

3. Bacteria and fungi cannot grow in salty conditions. Hence, salted foods

last longer.

4. Examples of food that can be preserved by salting are fish, meat, eggs,

vegetables and fruits.

5. Salting will change the taste, colour and destroy food nutrition.

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Pasteurising

1. Pasteurising is a process in which milk is heated at 63 °C for 30 minutes

or heated at 72 °C fo 15 seconds and followed by rapid cooling to below

10 °C.

2. The pasteurised milk can then be refrigerated to last a few days. 

3. Friut juice can also be preserved in this way.

4. This method of preservation retains the natural flavour of milk. Nutriens

like vitamins are not destroyed. 

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Canning/Bottling

1. Some foods can be canned and bottled. The canning and bottling of food

allows the food to be kept for a very long time.

2. These methods of preservation involve:

a) heating of the food to a very high temperature

- can kill bacteria and fungi

b) keeping foods in airtight cans or bottles - to prevent the entry of air

that may contain bacteria and fungi

3. Therefore, canned or bottled foods can be kept for a long time in months

or years.

4. Examples of food that can be perserved by canning or bottling are shown

below.

fish

meat

beans

corn

mushroom

chicken

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pineapple

condensed milk

jam

soft drink

soy sauce

syrup

tomato sauce

fruit juice

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Pickling

1. Food can be preserved by soaking it in an acidic solution (vinegar) or

saturated sugar solution. This process is known as pickling.

2. Bacteria and fungi cannot grow in acidic conditions or in saturated

sugar solutions.

3. Therefore, pickled foods last longer and cannot be spoilt easily.

4. However, its taste will be different and it becomes less nutritions.

5. Examples of food that can be preserved by pickling are fruits such as

mango, papaya and guava.

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Cooling and Freezing

1. Cooling ia a process in which foods are kept at low temperature (0°C-5C).

2. Examples of food preserved by cooling are vegetables, friuts, eggs,

margarine, cheese and milk.

3. Freezing is a process in which food is cooled at a very low temperature

below 0°C) until it freezes.

4. Examples of food preserved by freezing are fish, meat, chicken, prwans,

cuttlefish, meat balls and ice-cream.

5. Cooling and freezing can be done by keeping the foods in a refrigerator at

home.

6. In the case of cooling, the idea is to slow bacterial action so that it takes

food much longer (perhaps a week or two) to spoil.

7. In the case of freezing, the idea is to stop bacterial action altogether.

Frozen bacteria are completely inactive.

8. Bacteria and fungi becomes active again when the food is taken out from

the refrigerator.

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9. Therefore, after taking out food from the refrigerator, it must be cooked or

eated quickly before spoils.

10. The advantages of preserving food by cooling and freezing are :

a) the freshness a food is preserved.

b) nutrition content in the food is not destroyed.

Boiling

1. Boiled foods may last longer than unboiled foods.

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2. When food is boiled, all bacteria and fungi will be killed.

Drying

1. We can dry food to remove water from the food.

2. Without water in food, bacteria and fungi cannot grow. This can make the

food last longer.

3. Drying foods can be done as follows.

a) Drying the food under hot sun

b) Heating food to a high temperature

4. The disadvantage of this method is that the food becomes less nutritious

because some nutrition may be lost during the process.

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Smoking

Smoking is used to lengthen the shelf life of perishable food items. This effect is

achieved by exposing the food to smoke from burning plant materials such as

wood. Most commonly subjected to this method of food preservation are meats and

fish that have undergone curing.

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A collection of dried mushroomsA collection of dried mushrooms Drying salted fish

Vacuum packing

Vacuum-packing stores food in a vacuum environment, usually in an air-tight bag

or bottle. The vacuum environment strips bacteria of oxygen needed for survival,

slowing spoiling. Vacuum-packing is commonly used for storing nuts to reduce

loss of flavor from oxidation.

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5.0 ADVANTAGES AND DISADVANTAGES OF EACH FOOD PRESERVATION METHOD

Method Advantages Disadvantages

Drying (e.g. freeze-drying, spray-drying, sun-drying)

Produces concentrated form of food.

Inhibits microbial growth & autolytic enzymes.

Retains most nutrients.

Can cause loss of some nutrients, particularly thiamin & vitamin C.

Sulphur dioxide is sometimes added to dried fruits to retain vitamin C, but some individuals are sensitive to this substance.

Smoking Preserve partly by drying, partly by incorporation of substances from smoke.

Eating a lot of smoked foods has been linked with some cancers in some parts of the world.

Refrigeration Slows microbial multiplication.

Slows autolysis by enzymes

Slow loss of some nutrients with time

Freezing Prevents microbial growth by low temperature & unavailability of water.

Generally good retention of nutrients.

Blanching of vegetables prior to freezing causes loss of some B-Group vitamins and vitamin C.

Unintended thawing can reduce product quality.

Adding salt or sugar Makes water unavailable for microbial growth.

Process does not destroy nutrients.

Increases salt and sugar content of food.

High heat processing (e.g. pasteurisation)

Inactivates autolytic enzymes

Destroys microorganisms.

Loss of heat-sensitive nutrients.

Canning (involves high heat processing)

Destroys microorganisms & autolytic enzymes.

Water-soluble nutrients can be lost into liquid in can.

Chemical preservatives Prevent microbial growth

No loss of nutrient.

Some people are sensitive to some chemical preservatives.

Ionizing radiation Sterilizes foods (such as spices) whose flavour would change with heating.

Inhibits sprouting potatoes

Extends shelf life of strawberries and mushrooms

Longer shelf life of fresh foods can lead to greater nutrient losses than if eaten sooner after harvesting.

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6.0 LESSON LEARNED

From this assignment, we now understand how food can gets spoilt and that

we can prevent it by using food preservation methods. We also understand

that food preservation are important to ensure food do not go to waste and

that it help to keep the food in good condition as it is being transported from

one place to another far away. We had also learned the many ways food can

be preserved and each with its advantage and disadvantage.

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7.0 ACKNOLEDGMENT

We want to take this opportunity to thank teacher Puan Noraini our Science

teacher for giving us this opportunity to learn more about food preservation

through this assignment. We also want to thank our parents for their

guidance on how to use the internet to do research for this assignment.

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8.0REFERENCES

a) http://healthyeatingclub.com/info/articles/food-proc/food-pres.htm

b) http://www.nios.ac.in/SecHmscicour/english/LESSON_05.pdf

c) http://en.wikipedia.org/wiki/Food_preservationd) http://6laksamana.blogspot.com/2009/04/food-

preservation.htmle) http://fnorliezaa.blogspot.com

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