- 1 What Should You Know About Food Poisoning ? And What are Food Preservation methods ?
- 1.1 Preservation of Food
- 1.2 1. Preservation of Food by Sun-Drying (or Dehydration)
- 1.3 2. Preservation of Food by Heating
- 1.4 3. Preservation of Food by Cooling (or Refrigeration)
- 1.5 4. Preservation of Food by Deep Freezing
- 1.6 5. Preservation of Food by Common Salt
- 1.7 6. Preservation of Food by Sugar
- 1.8 7. Preservation of Food by Mustard Oil and Vinegar
- 1.9 8. Preservation of Food by Using Special Chemicals as Preservatives
- 1.10 9. Preservation of Food by Pasteurisation
- 1.11 10. Preservation of Food by Packing in Air-Tight Packets
Environmental biology is one of the critical Biology Topics that involves understanding how humans impact the environment and how to address environmental issues.
What Should You Know About Food Poisoning ? And What are Food Preservation methods ?
If the food is not covered properly, stored properly or preserved properly, then it gets spoiled by the action of micro-organisms (such as bacteria and fungi) on it. Micro-organisms that grow on our food sometimes produce toxic substances (poisonous substances).
The food spoiled in this manner starts giving foul smell and bad taste. Its colour may also change (see Figure). If such a food is eaten, it will lead to food poisoning.
The disease caused due to the presence of a large number of micro-organisms (like bacteria and fungi) in the food, or due to the presence of toxic substances in food formed by the action of micro-organisms, is called food poisoning. Thus, food poisoning occurs due to the consumption of food spoilt by some micro-organisms.
The major symptoms of food poisoning are : Vomiting, Diarrhoea (Loose motions), Pain in abdomen, Headache and Fever. Food poisoning can cause serious illness and even death. The micro-organisms (like bacteria and fungi) which cause food poisoning come into food from the air, dirty hands, unclean food containers, flies, cockroaches, insects, rats, or sick farm animals.
The two most common examples of bacteria which cause food poisoning are bacteria Salmonella and bacteria Clostridium botulinum. An example of fungus which causes food poisoning is Aspergillus. The spoiling of food is a chemical change.
Food is a very precious material. It should not be allowed to get spoiled, become useless, and cause food poisoning, etc. We ‘preserve ’ food to prevent it from getting spoiled. We will now discuss the preservation of food.
Preservation of Food
The food materials like milk, fruits, vegetables, meat, fish and cooked food, etc., get spoiled easily. This is because they contain a lot of water due to which the food-spoiling micro-organisms can grow in them easily. We can prevent the spoilage and contamination of easily spoilable food materials like milk, fruits, vegetables, meat, fish and cooked food, etc., by proper methods (or techniques) of food preservation.
The process in which the food materials are given a suitable physical or chemical treatment to prevent their spoilage is called food preservation. Some of the methods for preserving foods are :
- Sun-drying (or Dehydration)
- Cooling (or Refrigeration)
- Deep freezing
- Addition of common salt
- Addition of sugar
- Addition of mustard oil and vinegar
- Use of special chemical preservatives (such as sodium metabisulphite, sodium benzoate and citric acid)
- Pasteurisation, and
- Packing food in air-tight packets.
The method to be used for preserving a particular food material depends on the nature of the food material. Different types of foods are preserved by using different methods of preservation. The preservation of food by different methods will become clear from the following examples.
1. Preservation of Food by Sun-Drying (or Dehydration)
Drying (or dehydration) means removal of water from food materials which are to be preserved. Sun-drying (or dehydration) reduces the water content (or moisture content) of food materials and makes them dry. In the absence of moisture, the food does not get spoiled because the micro-organisms which spoil food do not grow in dry food.
The vegetables like Spinach (Palak, Saag), Methi leaves, Cauliflower and Peas (Mutter) are preserved in our homes by the sun-drying method. These dried vegetables can be stored safely for a long time and used whenever required. Grapes are preserved by drying to make raisins (kishmish).
2. Preservation of Food by Heating
Heating kills many micro-organisms and prevents the food from spoilage. So, some foods can be preserved , just by heating. For example, we boil milk to prevent it from spoilage. When we heat the milk during boiling, then the food-spoiling bacteria present in it get killed. So, the boiled milk remains good for a longer time. It does not get sour quickly.
3. Preservation of Food by Cooling (or Refrigeration)
Low temperature inhibits the growth of micro-organisms. So, the food-spoiling bacteria do not grow and multiply in cold conditions (having low temperature). Thus, when food is kept in a cold place (like that in a refrigerator), then the food does not get spoiled easily.
It remains fresh for a much longer period. The food materials like milk, kneaded flour (dough), cooked food (like cooked vegetables and pulses), and fresh fruits and vegetables are kept in a cool place like refrigerator to prevent their spoilage.
4. Preservation of Food by Deep Freezing
Preservation of food by deep freezing means preservation of food by excessive cold (at temperatures much below CPC). Deep freezing of food can be done by placing it in the ‘freezer compartment’ of our refrigerator or in special ‘deep freeze refrigerators’. When the food is kept in a deep freezer (whose temperature is much below CPC), the food gets frozen.
At the very low temperature in deep freezer, the growth of food-spoiling micro-organisms is prevented completely. Due to this, the frozen food remains unspoiled and fresh for long periods. Thus, food can be frozen in deep freezers and kept fresh even for months. This frozen food can be cooked and eaten whenever needed. Deep freezing method is used for the preservation of foods like meat, fish and their products ; fruits and vegetables.
5. Preservation of Food by Common Salt
Common salt prevents the growth of food-spoiling micro-organisms due to which it is used to preserve a number of food materials. Common salt has been used to preserve meat and fish for ages. Meat and fish are covered with dry salt to prevent the growth of bacteria. Such meat and fish do not get spoiled easily. They remain good for a long time.
Common salt is also used to preserve fruits such as raw mangoes, lemon and amla (in the form of their pickles) and tamarind (in the form of chutney). Common salt does not allow bacteria or fungus to grow on fruits and vegetables preserved in it. For example, if ripe mangoes are kept as such for some time, they rot and get spoiled but the raw mangoes preserved by using common salt in the form of pickle do-‘not get spoiled for a long time.
6. Preservation of Food by Sugar
Sugar is used as a preservative in making jams and jellies from fruits (see Figure). Sugar reduces the moisture content from the fruits which inhibits the growth of micro-organisms like bacteria which spoil the fruits, etc.
The fruits which are preserved in the form of jams and jellies by using sugar as preservative are : Apple, Ripe mango, Orange, Strawberry, Pineapple and Guava, etc. The fruits preserved in the form of food materials like jams and jellies can be stored safely for a considerable time and used later.
7. Preservation of Food by Mustard Oil and Vinegar
Mustard oil and vinegar (sirka) are widely used as preservatives for the preservation of fruits and vegetables in the form of pickles (achar) (see Figure).
The use of mustard oil or vinegar prevents the spoilage of fruits and vegetables because food-spoiling bacteria cannot live in such an environment.
Some of the fruits and vegetables which can be spoiled easily are preserved in the form of their pickles by using mustard oil or vinegar. Mustard oil and vinegar are used as preservatives for preserving fruits such as raw mango, amla and lemon, etc., in the form of their pickles.
8. Preservation of Food by Using Special Chemicals as Preservatives
The three special chemicals which are used as preservatives in the preservation of food are : Sodium metabisulphite, Sodium benzoate and Citric acid. Sodium metabisulphite and sodium benzoate are used to preserve foods such as jams, jellies, juices and squashes so as to save them from spoilage. And citric acid is used as a preservative in confectionary (sweets). These special chemicals kill the food-spoiling bacteria but they do not harm us.
9. Preservation of Food by Pasteurisation
A French scientist named Louis Pasteur has given an excellent method of preserving food. This method is called ‘pasteurisation after his name. The method of pasteurisation is used for the preservation of milk in big milk dairies, and it involves the process of heating, followed by quick cooling.
Milk is preserved by the method of pasteurisation as follows : First the milk is heated to about 70°C for 15 to 30 seconds to kill most of the bacteria present in it. Next, this hot milk is cooled very quickly to a low temperature to prevent any remaining bacteria from growing further. And then this milk is stored in cold (in refrigerators).
Pasteurised milk can be consumed without boiling because it is free from harmful micro-organisms. The milk that comes in packets also does not get spoiled for a fairly long time. This is because it is pasteurised milk.
10. Preservation of Food by Packing in Air-Tight Packets
These days, dry fruits and even vegetables are sold in sealed, air-tight packets to prevent the attack of micro-organisms on them. This helps the dry fruits and vegetables to remain unspoiled for a longer time.