how can we classify foods?

The act of classification is the systematic arrangement of information into groups according to some defined principles. Food processors differentiate the food items on the basis of their shelf life and PH value. The major factor that affects shelf life of food is the microbial spoilage. So food processors are interested in classifying the food commodities on the basis of perishability or PH value. Perishability defines water content in food and PH value defines acidity of any food. Water content can accelerate or declines microorganisms activity of spoilage and PH value can provide a platform for microbial attack.

Classification of foods based on perishability

All foods differ with respect to their keeping qualities. Some food commodities like wheat, rice and maize, can stay for longer period without showing signs of deterioration and spoilage, while fresh fruit, vegetables, meat, fish and milk will keep only for very short period. A difference in the storage life of foods can be made by keeping them under identical conditions. Thus, when fresh foods are kept at 22℃, beef, poultry and fish will remain acceptable for one day only, leafy vegetables for one to seven days, fruits and vegetables for one to 20 days and most root crops for 7 to 50 days. Dried commodities can keep for 350 days or longer. Thus, based on the shelf life food processors classifies all foods into three categories:

1. Stable foods

2. Semi-perishable foods

3. perishable foods

  Stable foods

 Water contnet :

                The stable foods have water content less than 15%.

Shelf life:

               As stable foods have very low moisture content so if they are stored in proper conditions they can stay as long as for three months to up to three years.

Example:

               Stable foods include most of legumes (chickpea, mash, lentils, Masoor etc.), dried fruits (dry dates, plums, almond, pistachio etc.), sugar, salt, dry cereals (wheat, maize, barley, rice millet etc.) and processed foods like pasta, noodles, dry snacks etc.

Spoilage:

                Normally they have very low moisture content so stable foods are resistant to spoilage by microbial attack however spoilage can be caused by chemical reactions such as browning of sugars and rancidity of oils leading to taints and off flavours. Spoilage can also be caused by physical factors like if we do not properly store the food in appropriate conditions like at suitable temperature, moisture and storage area where insects and rodents attack easily.

Semi-perishable foods

Foods that can be fit for human consumption for a fairly long period with little care in handling and storage are classified as semi-perishable foods

Water content:

              Semi-perishable foods have water content ranging from 60 – 90%.

Shelf life:

              They have normal shelf life from four weeks to four months. Potatoes and similar commodities can keep for a few months if they are not bruised and are stored under appropriate conditions of temperature and humidity in insect and rodent proof warehouses.

Example:

               In semi-perishable foods fresh commodities like onion, garlic, ginger, potatoes are included. Commercially processed foods like ice cream, cheese and some fried snacks like nuggets, meat, fish, poultry and dairy product are included.

Spoilage:

               Most semi-perishable foods get spoilage by microorganisms and autolysis. Microorganisms include in spoilage are bacteria and mould. Some fried foods get deteriorate by rancidity of fats and oils or browning in sugar by Millard reaction or formation of sugar crystals in ice cream can damage the structure of ice cream. Some physical factors also included in the spoilage of foods like temperature, moisture, light, insects and rodent, bruising or cuts in some part of food.

Perishable foods

 Water content:

                    Perishable foods have moisture content ranging from 80 to 95%.

Shelf life:

                     They have a shelf life from few hours to few days under appropriate storage conditions.

Example:

                  Foods includes in this category are fresh fruits such as oranges, guava, water melon, strawberry, Apple, pineapple, grapes etc. and vegetables include carrots, cabbage, spinach, lady finger, tomatoes  , meat and mat products, chicken, fish, eggs, bread, bakery products like biscuits, cakes, pizza, burger, cooked foods items, donuts, and dairy products like milk, butter, cottage cheese, and fresh cream.

Spoilage:

                     Perishable foods are readily spoiled by microbial attack and autolysis. These food items have higher water content so bacteria and molds can easily grow and spoil the food. Bread and oranges are normally spoiled by molds while dairy products are deteriorated by most bacteria if they are not stored in refrigerator at low temperature.