food hygiene
2006-11-27 8:16 am
Describe and explain FIVE different methods of food preservation and state their effectiveness in controlling food spoilage.
回答 (2)
2006-11-27 6:56 pm
✔ 最佳答案
Principles of food preservationsMicro-organisms, enzyme, chemical reaction of food components are the main causes of food spoilage.
So the principles of preservations are:
(1)Killing of micro-organisms
(2)Inhibition of microbial growth
(3)Removing micro-organisms
(4)Destroying enzyme
(5) Retardation of chemical changes
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More information about the food preservation, Please see the following website:
http://home.pacific.net.hk/~ppleung/Chem/preservation.htm#Ways%20of%20the%20prevention%20and%20their%20side%20effects
2006-11-29 14:27:14 補充：
詳細說明如下：i. Removal of moisture ii. Altering temperatureiii. Changing pHiv. Use of osmotic pressurev. Use of chemical additivesi. Irradiation 其他方法：i. Heat treatment.ii. Chilling and freezing(由於字數所限，詳細說明請看這個檔案)http://www.shwss.edu.hk/~hks/phenol.doc
2006-12-01 09:48:49 補充：
如果仍然有問題，歡迎隨時與我聯絡：[email protected]謝謝﹗
2006-11-29 10:11 pm
Methods of Food preservations
Methods of food preservation would help to prevent a large amount of food being wasted. Some of the preservation methods not only reduce the nutritive value of foods but causes harmful effect directly.
Preservative methods vary according to the food items and quantity of the items to be preserved. There are household and commercial methods of food preservation available. The principles of food preservation can be broadly classified into two types. They are -
Bactericidal method.
Bacteriostatic method.
Bactericidal method:
In these methods most of the micro-organisms are killed. Examples of bactericidal methods of preservations are cooking, canning, pasteurisation, sterilisation, irradiation etc.
Bacteriostatic method:
The principle of this method is prevention of multiplication of micro-organisms. This may be achieved by removal of water, use of acids, oil, or spices and by keeping in low temperature. The commonly used methods of this principle are drying, freezing, pickling, salting, and smoking. A layer of oil on the top of any food prevents growth of micro-organisms such as moulds and yeast's by preventing exposure to air. Spices like pepper and turmeric have little bacteriostatic effect.
House hold methods of preservation and sterilisation
Different methods are used for getting rid of micro-organisms and for food preservation.
1. Washing:
It is the first level defence. Food items should be washed in clean water to get rid of dirt, micro-organism, helminthic ova or cyst, insecticide etc. Avoid prolonged soaking in water and washing after cutting the vegetables and fruits. Major disadvantage of over washing and soaking is that the water soluble vitamins and minerals will be lost in this process.
2. Cooking:
Cooking is the most commonly used food preservative method. This also improves digestibility, taste, flavour, and appearance. If boiling temperature is maintained for a sufficiently long period during cooking will be sufficient to get rid of bacteria and most of the spores. But if low heat is used the spores may survive and at favourable temperature it may germinate releasing bacteria. On re-heating bacteria may get killed but the toxin that produced may survive. This may cause life-threatening diseases.
3.Dehydration
Preservation of foods by drying is one of the earliest and simplest techniques used for centuries. Dehydration is the process by which surplus water is removed with out drastically reducing the taste and nutritive value of the foods. Foods such as meat, fish, figs, apples, raisins, apricots, gooseberries, herbs, and vegetables are generally preserved by this method. They keep well because of the combination of the physical changes. In fruits as the moisture is removed the concentration of sugar goes up and this increased sugar concentration adds to the unfavourable conditions for bacterial growth.
4.Refrigeration
Refrigeration works on the principle that bacterial and enzymatic activities are minimal at low temperatures. Foods should be placed in the refrigerator as quickly as possible and it should be covered. This will also prevent foods from acquiring the flavour of the other foods.
Methods of food preservation would help to prevent a large amount of food being wasted. Some of the preservation methods not only reduce the nutritive value of foods but causes harmful effect directly.
Preservative methods vary according to the food items and quantity of the items to be preserved. There are household and commercial methods of food preservation available. The principles of food preservation can be broadly classified into two types. They are -
Bactericidal method.
Bacteriostatic method.
Bactericidal method:
In these methods most of the micro-organisms are killed. Examples of bactericidal methods of preservations are cooking, canning, pasteurisation, sterilisation, irradiation etc.
Bacteriostatic method:
The principle of this method is prevention of multiplication of micro-organisms. This may be achieved by removal of water, use of acids, oil, or spices and by keeping in low temperature. The commonly used methods of this principle are drying, freezing, pickling, salting, and smoking. A layer of oil on the top of any food prevents growth of micro-organisms such as moulds and yeast's by preventing exposure to air. Spices like pepper and turmeric have little bacteriostatic effect.
House hold methods of preservation and sterilisation
Different methods are used for getting rid of micro-organisms and for food preservation.
1. Washing:
It is the first level defence. Food items should be washed in clean water to get rid of dirt, micro-organism, helminthic ova or cyst, insecticide etc. Avoid prolonged soaking in water and washing after cutting the vegetables and fruits. Major disadvantage of over washing and soaking is that the water soluble vitamins and minerals will be lost in this process.
2. Cooking:
Cooking is the most commonly used food preservative method. This also improves digestibility, taste, flavour, and appearance. If boiling temperature is maintained for a sufficiently long period during cooking will be sufficient to get rid of bacteria and most of the spores. But if low heat is used the spores may survive and at favourable temperature it may germinate releasing bacteria. On re-heating bacteria may get killed but the toxin that produced may survive. This may cause life-threatening diseases.
3.Dehydration
Preservation of foods by drying is one of the earliest and simplest techniques used for centuries. Dehydration is the process by which surplus water is removed with out drastically reducing the taste and nutritive value of the foods. Foods such as meat, fish, figs, apples, raisins, apricots, gooseberries, herbs, and vegetables are generally preserved by this method. They keep well because of the combination of the physical changes. In fruits as the moisture is removed the concentration of sugar goes up and this increased sugar concentration adds to the unfavourable conditions for bacterial growth.
4.Refrigeration
Refrigeration works on the principle that bacterial and enzymatic activities are minimal at low temperatures. Foods should be placed in the refrigerator as quickly as possible and it should be covered. This will also prevent foods from acquiring the flavour of the other foods.
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