Unit 8 Food Preservation

Unit 8: Food Preservation

by Teacher Jeya

supply energy

provide basic provide heat
needs and
Why Food is
balanced nutrients important?

prevent diseases build the muscle
and repair

damaged tissue

What Happens if.....? SPOILAGE

Foods not stored properly i) smelly
ii) loss of texture
iii) slimy
iv) change in color
v) bad taste
vi) mouldy

Food spoilage means the original nutritional value, texture, flavour of the food are damaged and
can no longer be consumed by humans

Nutrients Air not feasible or slow
growth at too high/
Factors causing the too low temp.
food spoilage
Temperature

5-65˚C suitable
temperature for
microbe growth

Water Acidity

Characteristics of Food Spoilage

Canned Foods: Swollen top or bottom, dented area along the side seam. Unusual odour of

contents.

Fruits & vegetables: Sunken, soft areas, browning, mouldy.

Fish: Gills discolored. Eyes sunken, flesh is easily pulled away from bones. soft when pressed;

rigidity not present. Foul odour.

Meat: Beef usually spoils first on surface while pork spoils at the juncture of bone and meat in

the inner portions. Foul odour is generally detectable and the meat is slimy to the touch.

Poultry: Stickiness appears first under the wing, at the juncture of legs and body as
well as darkening of the tips of the wings.

Frozen foods: Spoilage is promoted by thawing at room temperature, which
provides optimal conditions for the growth of bacteria. Foods should be thawed in
the refrigerator.

Milk products: Unpleasant smell, sour taste, bubbly/frothy, change in texture

Wheat products: black spots, sour sell, mouldy, mushy, slimy



Food Preservation - method of food processing to prevent or slow down the life processes of
microorganisms

Why food preservation is important:

v To minimize pathogenic bacteria – food in long-term storage is at serious risk of spoilage due to bacteria such as coli,
Salmonella, and other pathogens. Bacteria only need warmth, moisture, and time to rapidly multiply in food, but
food preservation inhibits one or more of these conditions and stops their growth.

v To keep food at its best quality – food deteriorates over time due to spoilage. In many cases, mild spoilage doesn’t
make food unsafe to eat, but it significantly affects its taste, texture, and appearance. Proper food preservation can
help retain some of these qualities, as well as the nutritional value of certain foods.

v To save money – waste is costly, both at home and in a commercial setting. Ideally, you should avoid buying more
than you can use, but various preservation methods – if done safely – help you keep vegetables, fruits, meat, etc.
well past their usual expiration so there’s no need to bin them.

v to ease transportation of food to areas affected by disasters such as flood or earthquake.

v seasonal fruits can be enjoyed throughout the year.



Drying is the oldest method of food preservation. This method reduces water activity which prevents bacterial growth.
Drying reduces weight so foods can be carried easily. Sun, wind or household dryers are used for drying.
Eg: Meat, seafoods, chillies and fruits like apples, apricots and grapes.

Adv: removes moisture to inhibit activity of microbes.
Disadv: some nutritional property will be damaged by heat hence redusing the quality of food.

Freezing is keeping prepared food stuffs in cold storages (0˚C or lower). Eg: Meat and seafoods
Cooling is below 18˚C. Potatoes can be stored in dark rooms but potato preparations need to be frozen.
Eg: Eggs, fruits and vegetables
Adv: does not the physical properties of the food

: nutritional properties maintained.
Disadv: too low temperatures may cause injury to the fresh products. Eg: fruits and vegetables.

Smoking is the process of drying food with smoke for a long period of time. Smoke is antimicrobial and antioxidant and
most often meats and fish are smoked.

Disadv: Smoking as a preservative enhances the risk of cancer.

Vacuum packing created by removing air from packaging. Since there is no oxygen in the created vacuum,
bacteria die.
Eg: dry fruit, dried meat/fish

Disadv: proper gas levels must be known to increase shelf life; loss of preservation once packaging opened,
expensive

Salting and Pickling: Salting also known as curing removes moisture from foods like meat. Pickling means preserving
food in concentrated sugar solution, brine (salt solution) or marinating in vinegar (acetic acid). Salt kills and inhibits
growth of microorganisms at 20% of concentration.
Eg of salting: fish, egg, vegetables
Eg of pickling: fruits, onion, soybean, petai, chilli

Disadv: alters food taste permanently

Waxing: pocess of coating fruits or vegetables with very thin layer of liquid wax. This prevents growth of
microorganisms on the surface and ensure the freshness of the food.

Adv: improve appearance of the produce, reduce moisture loss
Disadv: off-flavor development, artifical appearance.

Pasteurization: process of heating food to certain temperature for some time followed by rapid cooling.
Eg: Milk, canned food

Adv: Longer shelf life, taste retained.
Disadv: many nutrients and good bacterias might get destroyed due to high heat

Boiling: process of heating food at 100˚C to kill most bacteria.
Eg: liquid foods.

Disadv: Thermal resistant bacteria may still survive.

Canning/ bottling: best methods to prevent reproduction of bacteria and fungi for a longer period. They are heated
until 115˚Cto kill the microbes and the cap is closed tightly so that the germs cannot go in.
Eg: drinks, fish, meat, vegetables. oil, milk, fruits

Adv: the canned/ bottled food are suitable to be exported to other countries because they lasts longer.
Diasdv: food will be spoilt if the can is rusty or leaking; canning changes the taste and nutritional values of the food.

The Importance of Food Preservation Technology in daily life

Food preservation adds variety to the food. For example, in the absence of fresh peas during the hot
summer months, canned or dehydrated peas may be made use of.

increases the shelf life of food. Pineapples, cherries and other fruits and vegetables may be preserved
by different methods for long periods of time.

increases the food supply Soldiers in a war can easily carry preserved foods than fresh foods.

decreases the wastage of food. Excess foods which would have otherwise been wasted, when pro-cessed and
preserved add to the existing supplies, thus also decreasing the wastage of food.

decreases dietary inadequacies. Variety in diet is brought about with the help of preserved foods. For example, some
Middle-East countries do not grow any vege-tables due to arid soil conditions, This shortcoming is over-come through the
import of fresh and preserved fruits and vegetables.



Questionaire

1. Give 2 examples of foods that can spoil easily.

2. state the characteristics of the spoilt food.

3. State 2 conditions needed for fungi and bacterial growth.

4. Name the following preservation methods:
a) using a bath of salt or sugar solution
b) coatong the food with a thin layer of wax
c) heating food to a certain temperature for a while, followed by rapid cooling

5. give a reason why bacteria cannot live in food preserved using vacuum packaging method?

6. What is the importance of food preservation technology?