NUTRITIVE VALUE OF MEAT, POULTRY, EGG AND FISH
Meat refers to the flesh of warm blooded, four legged animals chiefly cattle, sheep and pigs. Meat of sheep which is under 12 months age is sold as lamb. After the age of 12months, it is called mutton.
Pork is the meat of swine (pig) slaughtered between the age 5 and 12 months. Veal is the meat of cattle that is slaughtered 3 to 14 weeks after birth.
If slaughtered between 14 to 52 weeks the meat is called calf. Meat obtained from cattle slaughtered one year after birth is called beef.
Meat is a very good source of protein. The average protein content of meat varies from 16 - 25 percent. The amino acid pattern of meat protein is of outstanding nutritive value. The fat content of meat varies from 5 - 40 percent.
Depending on the type, breed and age of the animal, fat is distributed throughout meat in small particles of large masses. Fat deposited uniformly in small sheets in the connective tissue within the muscle is called 'marbling'. This contributes tenderness and flavour to the meat.
Meat fats are rich in saturated fatty acids. The cholesterol content of meat is 75 mg / 100 gm. Carbohydrate is found in small quantities and present in the form of glycogen and glucose.
Meat is a good source of iron, zinc and phosphorpus. It also contains sodium and potassium. It is an excellent source of B-complex vitamin particularly B12 which is absent in plant foods. Liver is an excellent source of iron and vitamin-A.
Changes in Meat :
After slaughtering, the lean tissues undergo a series of complex physical and chemical changes. As a result muscles loose their soft pliable nature and become rigid, stiff and inflexible. This is termed as 'rigor mortis'.
Stiff muscle starts to soften and becomes tender when it is held in a cold room temperature between 0 o C to 20 o C for 1 - 4 weeks. This is known as 'ripening' or 'ageing'.
During ageing the humidity of the room is to be controlled. Tenderness of meat can also be obtained by the use of mechanical methods such as pounding, cutting and grinding which break muscle fibre. Addition of salt, vinegar, lime juice and enzymes viz., papain, bromelin and ficin also help in tenderising meat.
Changes that occur during cooking:
· On heating, the red pigment turns brown due to the denaturation of protein pigment.
· Heat treatment also brings about inactivation of enzymes and denaturation of proteins, which makes meat tougher. Hence, adopting correct cooking methods, time and temperature will result in a well-cooked product.
· Heating results in release of volatile compounds from both fat and lean meat which contributes to the flavour and taste of cooked meat.
· Heating melts meat fat which increases palatability of meat when eaten warm.
· There is loss of water on heating which does not change the nutritive value but may affect juiciness and bring about shrinkage in volume and weight.
Minerals like calcium may be lost in meat dripping due to the dissolution of calcium from bones. There is loss of B-vitamins also.
The term poultry refers to domestic fowls reared for their flesh and egg. It includes chicken, duck, geese, turkey, pigeon etc.
Poultry meat has a high protein content varying from 18 to 25 percent. It contains all the essential amino acids required for body building.
Fat content of poultry is influenced by age and species of the bird. Young birds have little fat content. Chicken fat is unsaturated and is therefore better than the fat of red meat. Poultry flesh is a good source of B-vitamin and minerals.
The term egg mainly refers to the egg of hen and duck. An average egg weighs 50 gms. approximately and is composed of the shell, egg white and yolk. The weight is distributed in the different parts as follows.
Percentage composition of egg
Shell 8 - 11
White 55 - 61
Yolk 27 - 32
Egg is a rich source of protein and lipids. Egg protein is of high quality as compared to any dietary protein and therefore is used as a standard for evaluating the protein quality of other foods. The nutrient composition of egg white and yolk differ considerably and is represented in the following table.
Percentage nutrient composition of egg white and yolk
Nutrient Egg white Egg yolk
Water 88.0 % 48.0 %
Protein 11.0 % 17.5 %
Fat 0.2 % 22.5 %
Mineral 0.8 % 2.0 %
Vitamin and minerals in Egg:
Egg yolk is rich in vitamin-A. Thiamin and riboflavin are present in appreciable amounts. Calcium is present in the yolk in small amounts.
Phosphorus is abundant in the yolk. Eggs are an important source of bioavailable iron and a fair source of sodium, magnesium chlorine, potassium and sulphur.
Fishes are classified as shell fish and fin fish. The nutrient composition of fish of a given species varies depending on the season of year and maturity. However most fish contain 15 - 24 percent protein, 0.1 - 22 percent fat and 0.8 - 2 percent minerals.
Fish proteins are easily digestable and are of high biological value. The fat content is influenced by the species, feeding habits and maturity of fish. Glycogen is present in fish but is in lesser quantities than meat.
Fish oils are an excellent source of vitamin A and D. They are a good source of thiamin, riboflavin and niacin. Small fishes that can be eaten with bones contribute a significant amount of calcium.
Ocean fish are a rich source of iodine. Oysters are an excellent source of copper. Fishes contain omega - 3 polyunsaturated fatty acids. These acids are found to prevent the degeneration diseases of the heart.