Food Preservation Print
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Transcript of Food Preservation Print
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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