Composition and nutritive value

Lesson 6 : Cereals- Composition, Processing and Utilization

Composition and nutritive value

Nutritive value of different cereals is given in table 2.1

  • Energy: Cereals are the main source of energy, contributing 70-80 percent of the requirement. Hundred grams give more than 340 kcal of energy.

  • Carbohydrates: 80 percent of dry matter of cereals is carbohydrate. The two carbohydrates present are crude fibre and soluble carbohydrate. The fibre constituents are cellulose, hemicelluloses and pentosans which are concentrated 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. Of all the cereals, whole wheat, ragi and bajra contain high amount of fibre.

  • Protein: The protein content of different cereals varies. 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. The gliadins and glutelins are known as gluten proteins. The gluten has unique elasticity and flow properties which are used for baking bread and other products.

    Cereals contain 6-12 percent protein, which is generally deficient in lysine. They provide more than 50 percent of protein requirement as they are consumed in large quantities. Among cereals, rice protein is of better quality than the others. Cereals, when consumed with pulses, the protein quality improves due to mutual supplementation. Cereals are deficient in lysine and rich in methionine. Pulses are deficient in methionine and rich in lysine. Hence, there is improvement in protein quality of both proteins.

  • Lipids: Lipidsare present to the extent of 1-2 percent in wheat and rice, and 3 percent in maize. More lipids are present in germ and bran than in other parts of the grain. Wheat germ contains lipids 6-11 percent and bran 3-5 percent and endosperm 0.8-1.5 percent. Lipid content of maize germ is 35 percent and the bran contains 1 percent. The lipids are mostly the triglycerides 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 percent of our essential fatty acid requirement. Cereals together with pulses can nearly meet the essential fatty acid requirement of an adult.

  • Minerals: About 95percent of minerals are the phosphates and sulphates of potassium, magnesium, and calcium. A considerable part of phosphorous in cereals is present in the form of phytin. Phosphorous 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. Off germination of the grains, the phytate content reduces due to enzymatic breakdown and iron availability is improved.

    Some mineral elements like copper, zinc, and manganese are also present in very small quantities in cereals.
    Cereals are poor sources of calcium and iron particularly rice is a very poor source of these two elements. The content depends upon the extent of polishing. Ragi is a rich source of calcium and iron. Millets (ragi, bajra, jowar) are rich in minerals and fibre. The iron content of wheat is increased during milling where iron rollers are used.

  • Vitamins: Whole grain cereals are an important source of B vitamins in our diet. Since most of these vitamins are in the outer bran, refining or polishing the grains reduces B vitamin content. Parboiling which includes soaking in water and steaming of paddy results in seeping of vitamins present in outer layer into the grain. Hence, milled and polished parboiled rice retains much of the B 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.
    Nutritive value of wheat and rice is compared in the figure 2-b.

  • Enzymes: Certain grains contain many enzymes and of these the amylases, proteases, lipases and oxido-reducatases are of importance. Upon germination α 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.
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Last modified: Thursday, 8 December 2011, 7:12 AM