Food Test: Identification of food nutrients

IDENTIFICATION OF FOOD NUTRIENTS

Carbohydrates

1. Iodine test: cut a section of carbohydrate food to expose the flesh. Then pour drops of iodine on the exposed flesh. If it turns black or darkish brown, it shows the presence of carbohydrate. If it remains light brown, then carbohydrate is absent.
2. Litmus test: this is another simple experiment to detect the presence of carbohydrate in any food substance. The food item is peeled if it has any bark.it is then grated and made into a paste. Red litmus paper is immersed into the paste, if it turns blue it shows the presence of carbohydrate but if it remains unchanged, it does not contain any carbohydrate.

Proteins

1. Foam test: a very simple test for the presence of protein, is todissolve the food substance in water and shake vigorously. If a foam is produced, it shows the presence of protein. Absence of foam indicates that the food substance does not contain protein.
2. Alcohol test: alcohols have a coagulating effect on proteins. Thus if a food product or its solution coagulates, shrinks or curdles when immersed in alcohol, it shows that food is proteineous. In the case of meat apart from shrinking, its color also changes to brown.
3. Million’s test: million’sreagent may be used to detect the presence of protein in foodstuffs. A solution of the foodstuff is warmed with million’s reagent (which contains mercurous and mercuric nitrates in nitric acid). If protein is present, a white precipitate which later turns red is obtained. The only common protein which does not give a positive result with this test is gelatin. 

Fats

Blotting paper test: the presence of fat in any foodstuff can be detected by grinding a small quantity of foodstuff between two pieces of blotting or filter paper. If after grinding, the paper or some portion on it becomes translucent or greasy, it shows the presence of fats or oil in the foodstuff. If not, it indicates the absence of fat.

FOOD COMPOSITION TABLE      

Food composition table is a table that shows in a tabular form the nutritive value (amounts of nutrients) of common food commodities be they raw, processed or cooked.

A food composition table serves many purposes. The purposes are as follows.

1. Gives ready and useful information about the nutritive values of the major food commodities thereby preventing misinformation of consumers by processors and marketers of food.
2. It is used to compare the food values of one food with another and helps consumers to choose foods according to their needs.
3. It is used for planning meals which meet specific needs for specific groups of people such as infants, adolescents, aged etc.
4. It is used to calculate the nutritional contents of food with a view to comparing them with standards in order to determine whether a food meets Recommendation Daily Allowance (RDA) for nutrients or not.

The food composition table is affected by the following factors:

1. The nature and type of the soil used to grow the commodity.
2. The variety of the plant or breed of the animal.
3. The age of the animal will affect the composition of meat and milk obtained from them.
4. The type of feed given to animal and poultry livestock will also affect the composition meat, milk and eggs from these animalsand birds.
5. The climatic condition during the growth of plants.
6. The handling and storage methods.

Evaluation: state the purposes of the food composition table

• State the disadvantages of food composition table

Assignment: Read Meal planning