Classification of food

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Classification of food
Introduction:
For the conventional selection of food, food is classified on many bases. One of them is on the basis of their perishability and the other is on the bases of pH. These classifications are the main parameters of concern for a food processor. The industrial world that prepares commercial food products consider these classifications while food packaging and keep them in view to decide the preservative which in turn will decide the shelf life. In this article, the classification details of food on the bases of both parameters that are perishability and pH will be discussed.
Types of Classification of food:
Food is classified on two bases. These are:
On the basis of perishability
On the basis of pH
On the basis of perishability:
All foods differ with respect to their keeping qualities. Some commodities survive for a longer period e.g wheat, rice etc that has low water content but those with high water content are highly perishable and spoils faster e.g vegetables, fruits, milk, meat and milk. On the basis of perishability, food is classified into three main types:
Stable foods
Semi-perishable
Perishable foods
Stable foods:
Stable foods are those foods that remain preserved and acceptable for a longer period of time ranging from at least three months to three years maximum. The foods that fall in this category are:
Wheat
Rice
Maize
Barley
Millet
Sorghum
Honey
Legumes (cowpeas, chickpeas, lentils)
Sugar
Processed foods such as powdered milk, pasta and breakfast cereals are also considered in this group.
The agents which are responsible for food spoilage don’t spoil the stable foods as they don’t find the favourable environment in them for their growth and to run their disease cycle. It is mainly because of the low moisture content that is about less than 15%. But fungus can grow in them too as it is a highly resistant organism found in nature.
Semi-perishable foods:
Semi-perishable foods are those that can survive or preserved for a little longer period with a bit of care during storage and handling. Their shelf life usually ranges from a few weeks to few months. This category involves the foods with fresh nature such as:
Ginger
Potato
Some varieties of apples
Garlic
Onion
Some processed foods e.g fried snacks, few varieties of cheese and ice cream, that usually have shelf life of 4 months are also included in it.
Semi-perishable foods are spoiled by the processes of autolysis and microbial attack especially bacteria and some moulds. The moisture content of semi-perishable foods ranges between 60 to 90%. However, still they are little stable despite of high moisture content. The reason for their stability is due to their special structure and composition that protects them against spoilage.
Perishable foods:
Perishable foods have shelf life of a few hours to a few days under proper storage conditions. Foods classified in this group are:
Milk
Meat
Eggs
Fruits
Vegetables and;
Fruits
Cottage cheese
Fresh cream
Fresh bakery products
Heated canned foods are treated as perishable when opened.
Such foods can be stored at low temperature e.g in refrigerator that increases their shelf life. The maximum storage life of such foods is 4 weeks. The moisture content in these foods usually ranges from 80 to 95%. The perishable foods are readily spoiled by autolysis and microbial attack especially bacteria.
On the basis of pH:
This classification provides information on:
The possible spoilage organisms
Food poisoning micro-organism
The choice of heat processing temperatures
On the basis of pH, the foods can be classified into the following:
High acid foods
Acid foods
Medium acids and;
Low acids
High acid foods:
High acid foods have pH below 3.7. This group includes:
Most citrus fruits
Pickles
The spoilage organisms are usually yeast and moulds. Aciduric bacteria are also responsible for their spoilage. These organisms are destroyed by pasteurization temperature that is 65-88 centigrade.
Acid foods:
Foods within the pH range of 4.5 to 3.7 are included in this class. This group involves:
Guava
Oranges
Mangoes
Pineapples
Tomatoes and; other fruits.
Naturally occurring enzymes and non-spore forming Aciduric bacteria usually spoil them. They can be destroyed by pasteurization.
Medium acids:
Medium acid foods have pH between 4.5 and 5.0. The foods that fall in this category are tomatoes and its sauces. They are spoiled by spore forming bacteria. These microbes can be destroyed by sterilization.
Low acids:
These foods are most sensitive to bacteria especially spore forming bacteria. pH ranges from 5 to 6.99. the foods in this category are:
Milk
Eggs
Meat
Fish
Poultry
Vegetables
They can be saved by sterilization.
Conclusion:
So, in a nut shell foods are preserved and consumed on the basis of their classification. This classification is really meaningful for food processors.

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