1. Food can spoil after a certain period of time.
2. Spoilt food will change in texture and taste.
3. One can get food poisoning by eating spoilt food.
a) Food poisoning can lead to stomach upset, diarrhea and vomiting.
b) Serious food poisoning may cause death.
4. Foods which are spoilt can be identified by observing, touching, smelling and tasting.
5. Spoilt food has one or more of the following characteristics.
a) Unpleasant smell
b) Unpleasant taste
c) Changed colour
d) Changed texture
1. Food preservation is a process that makes food last longer.
2. Food preservation can prevent or slow down the action of bacteria or fungi on the food.
3. There are many methods to preserve food.
- Vaccum packing
- Bottling & Canning
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.
1. Boiled foods may last longer than unboiled foods.
2. When food is boiled, all bacteria and fungi will be killed.
Cooling and Freezing
1. Cooling is a process in which foods are kept at low temperature (0°C - 5 °C).
2. Examples of food preserved by cooling are vegetables, fruits, 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, prawns, 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 become active again when the food is taken out from the refrigerator.
9. Therefore, after taking out food from the refrigerator, it must be cooked or heated 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
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.
6. Mango pickling can be done as follows.
a) Cut some green mangoes.
b) Wash and drain the mango slices.
c) Mix the mango slices with salt and leave them overnight.
and drain the mango slices again. Wash
e) Soak the mango slices in sugar solution for several days.
f) Add a little bit of vinegar and seal the bottle tightly.
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.
- condensed milk
- soft drink
- soy sauce
- tomato sauce
- fruit juice
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.
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.