Wheat: Milling process and products

It belongs to the genus triticum and there are 30,000 species. The kernel of wheat is usually 1/8-1/4 inch long.

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Cereals and cereal products

The term cereal is not limited to the principal cereal crops like rice, wheat, maize or corn, jowar, ragi and bajara but also flours meals, breads and alimentary pastes or pasta. The ease with which grains can be produced and stored, together with the relatively low cost and nutritional contribution has resulted in wide spread use of cereal foods. Cereals are the staple foods in the diets of most population groups.

Composition and nutritive value

Carbohydrates: 80% of dry matter of cereals is carbohydrate. The two carbohydrates present are crude fiber and soluble carbohydrate. The fiber constituents are cellulose, hemicellulose and pentosans. Of the soluble carbohydrate, starch is the most important carbohydrate in all cereals. Small quantities of dextrin and sugars are also present. Free sugars present include simple sugars such as glucose and disaccharides like sucrose and maltose.

Protein: The protein content varies as per different cereals. Rice contains less amount of protein compared to other cereals. The protein content of different varieties of the same cereal also varies. Proteins are found in all the tissues of the cereal grain. Higher concentrations occur in the embryo, scutellum and aleurone layer than in the endosperm, pericarp and testa. Within the endosperm the concentration of protein increases from the centre to the periphery. The types of protein present in cereals are albumins, globulins, prolamines (gliadins) and glutelins. The proportion of these proteins differs in different cereals.

Lipids: Lipids are present to the extent of 1-2% in wheat and rice, and 3% in maize. More lipids are present in germ and bran than in other parts of the grain. Wheat germ contains lipids 6-11% and bran 3-5% and endosperm 0.8-1.5%. Lipid content of maize germ is 35% and the bran contains 1%. The lipids are mostly the triglycrides of palmitic, oleic and linoleic acid. Cereals also contain phospholipids and lecithin.Considering the amount of cereal consumed it is estimated that fat present in cereals in our diets can meet more than 50% of our essential fatty acid requirement. Cereals together with pulses can nearly meet the essential fatty acid requirement of an adult.

Minerals: About 95% of minerals are the phosphates and sulphates of potassium, magnesium and calcium. A considerable part of phosphorus in cereals is present in the form of phytin. Phosphorus and calcium present in phytin are not available for absorption. Phytates present in cereals decrease the absorption of iron. Unrefined cereals contain more phytates than refined or polished cereals. On germination of the grains, the phytate content reduces due to enzymatic breakdown and iron availability is improved. Some mineral elements like copper, zinc, manganese are also present in very small quantities in cereals.

Vitamins: Whole grain cereals are an important source of B vitamins in our diet. Since most of these vitamins are in the outer bran hence refining or polishing the grains reduce B vitamin content. Parboiling of paddy results in seeping of vitamins present in outer layer into the grain. Hence milled and polished parboiled rice retains much of the vitamins. Maida has less B vitamins than whole wheat flour. Cereals do not contain either vitamin A or C except maize, which contains small amount of carotenes. Oils from cereal grains are rich in vitamin E.

Enzymes: Certain grains contain many enzymes and of these the amylases, proteases, lipases and oxido-reductases are of importance. Upon germination a amylase activity increases. The proteases are relatively more in the germ. The lipases of the cereals are responsible for the fatty acids appearing during storage of the cereals and their products.

Nutritive value of different cereals