Structure, Composition and Nutritive Value of Cereals, Millets and Pulses PDF

Script Structure, Composition and Nutritive value of Cereals, Millets and Pulses CEREALS; INTRODUCTION They belong to the family graminecae (grass). Seed is commonly called as grain/ caryopsis; they are cultivated for seeds which provide a staple food for humans. It is main source of CHO in t...

Script Structure, Composition and Nutritive value of Cereals, Millets and Pulses CEREALS; INTRODUCTION They belong to the family graminecae (grass). Seed is commonly called as grain/ caryopsis; they are cultivated for seeds which provide a staple food for humans. It is main source of CHO in the diet of many nations. Each cereal has unique properties which make it suitable for a variety of food products. Different cereals are better grown in different regions of the globe; they require different conditions to grow. Ex: rice -wetter warm temperate, subtropical & tropical climates, Wheat &Barley in temperate regions of Europe & Asia, Rye & oats in cold regions of Northern & Eastern Europe. Cereals are best energy food; they are inexpensive as compared with foods of animal origin. This includes staples such as wheat, rye, oats, barley, millet, rice, and sorghum. All grains have the anatomy as given in the figure below. STRUCTURE OF CEREAL GRAINS The cereal crops that are grown for their edible fruit are generally called grain, but botanically referred to as caryopsis. The cereal seed consists of two major components, the endosperm and embryo or germ. The endosperm encompasses the bulk of the seed and is the energy source of stored food. It contains mostly starch, some protein and some B-vitamins.An outer wall called the pericarp that develops from the ovary wall encases the endosperm. A semi permeable layer under the pericarp, which is called testa, surrounds the embryo and is derived from the inner ovary wall. The third layer, which is called aleurone, contains thick-walled cells that are free of starch. The pericarp, testa, and aleurone layer are collectively called the bran. Bran is high in fiber, B-vitamins and minerals and is removed during milling and polishing. The germ is permeable to water, but not to the dissolved salts, and is important for germination. Germ is rich in B-vitamins, minerals, lipids especially vit E and phytochemicals. Germ is also separated from the grain during milling. COMPOSITION AND NUTRITIVE VALUE OF DIFFERENT CEREALS Compositionally, cereals consist of 12-14 percent water, 65-80 percent carbohydrates, 2-6 percent lipids and 7-12 percent protein. Cereals are quite similar in gross composition being low in protein and high in carbohydrates. Energy: Cereals are the main source of energy, contributing 70-80% of the requirement of Carbohydrates: 80% of dry matter of cereals is carbohydrate. The two carbohydrates present are crude fiber and soluble carbohydrate. The fiber constituents are cellulose, hemicelluloses 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. Of all the cereals, whole wheat, ragi and bajra contain high amount of fiber. Protein: The protein content of different cereals varies 6-12%. Rice contains less amount of protein compared to other cereals. The protein content of different varieties of the same cereal also varies. Proteins are formed 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 center to the periphery. The types of protein present in cereals are albumins, globulins, prolamins (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% protein, which is generally deficient in lysine. They provide more than 50% 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 and pulses are rich in lysine. Hence there is improvement in protein quality of both proteins. 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. 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% 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 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 fiber. 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 of the grains reduce 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. Enzymes: Certain grains contain many enzymes and of these the amylases, proteases, lipases and oxido-reductases 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. Antinutrients in cereals Cereals and other plant foods may contain significant amounts of toxic or antinutritional substances. Most cereals contain appreciable amounts of Phytates, enzyme inhibitors, and some cereals like sorghum and millet contain large amounts of polyphenols and tannins. Some of these substances reduce the nutritional value of foods by interfering with mineral bioavailability, and digestibility of proteins and carbohydrates. Composition of grains and legumes Grain Protei Fa Crud As Starc Total Carbohydr Moisture n% t e h h% sugar ate % % fiber % s% % % Wheat 15.3 1. 2.9 1.8 53.0 2.6 72.0 14.0 9 Barley 8-13 2- 5.6 2- 65.0 2-3 77.0 14.0 3 2.5 Corn 10.0 4. 2.9 1.5 70-72 3.22 71.0 14.0 3 Oat 17.3 5. 12.1 3.4 52.8 1.45 66.0 14.0 1 Brown 7.3 2. 0.8 1.4 80 1.0 64.3 13 rice 2 Rye 8.7 1. 2.2 1.8 75-76 0.5 72.3 14.0 5 Soybea 40.0 21 5.3 4.9 12-14 16.6 34.0 12.0 n  Comparative nutritive value of cereal grains FACTOR Wheat Maize Brown Barley Sorghum Oat Pearl Rye rice millet Available 69.7 63.6 64.3 55.8 62.9 62.9 63.4 71.8 CHO (%) Energy 1570 1660 1610 1630 1610 1640 1650 1570 (kJ/100 g) Digestible 86.4 87.2 96.3 81.0 79.9 70.6 87.2 85.0 energy (%) Vitamins (mg/100 g) Thiamin 0.45 0.32 0.29 0.10 0.33 0.60 0.63 0.66 Riboflavin 0.10 0.10 0.04 0.04 0.13 0.14 0.33 0.25 Niacin 3.7 1.9 4.0 2.7 3.4 1.3 2.0 1.3 Amino acids (g/16 g N) Lysine 2.3 2.5 3.8 3.2 2.7 4.0 2.7 3.7 Threonine 2.8 3.2 3.6 2.9 3.3 3.6 3.2 3.3 Met. & Cys. 3.6 3.9 3.9 3.9 2.8 4.8 3.6 3.7 Tryptophan 1.0 0.6 1.1 1.7 1.0 0.9 1.3 1.0 Protein quality (%)  True 96.0 95.0 99.7 88.0 84.8 84.1 93.0 77.0 digestibility Biological 55.0 61.0 74.0 70.0 59.2 70.4 60.0 77.7 value Net protein 53.0 58.0 73.8 62.0 50.0 59.1 56.0 59.0 utilil. Utilization 5.6 5.7 5.4 6.8 4.2 5.5 6.4 5.1 protein Barley, sorghum, rye and oat proteins have lower digestibility’s (77-88%) than those of rice, maize and wheat (95-100%). The biological value and net protein utilization of cereal proteins is relatively low due to deficiencies in essential amino acids and low protein availability The digestible energy of rice is significantly better than that of other cereals. WHEAT (Triticum spp.) It is a grass that is cultivated in temperate zone. The most important human food grain and ranks second in total production as a cereal crop behind maize; the third being rice. Wheat grain is a staple food used to make flour for chapattis breads; cookies, cakes, pasta, noodles and breakfast cereals. SEMOLINA: Crushed (not rolled) endosperm of wheat.Used for preparing breakfast dishes, for thickening soups, in preparation of pasta & in milk puddings. MAIZE (Zea mays L.) Corn or maize is an important cereal crop in North America. Corn apparently originated in Mexico and spread northward to Canada and southward to Argentina. The grains are about the size of peas, the starch found mainly in the endosperm, comprises 70-72 % of the kernel. Young and tender maize is eaten as a vegetable (sweet corn).Whole corn is processed as breakfast cereal. Fully ripened maize is ground into flour used as thickening agent (corn flour).It also yields oil suitable for cooking.  RICE (Oryza sativa) Rice is the most important cereal crop in developing world as it is a significant staple food for a large part of the world's human population.90% crop of rice is grown in southern & eastern Asian countries. It is least nutritious of all cereals, containing more starch & less protein, fat, and minerals.Rice is eaten white after removal of bran & germ. BARLEY :( Hordeum vulgare L) Barley is a major cereal grain. Barley also belongs to the grass family and is one of the major ancient world's crops. It contributes to the human food, malt products, ranks in the top ten crops, and is fourth among the cereals. OATS :( Avena sativa) Oats are grown for both grain and forage needs While oats are suitable for human consumption as oatmeal and rolled oats, one of the most common uses is as livestock feed. Have a high protein and fat content but no gluten for which it is unsuitable for bread making.Highest food value of any of the cereals, used for making biscuits, cakes and porridge. Oats are generally considered health food. The discovery of cholesterol-lowering components the beta-glucans has led to wider appreciation of oats as human food RYE: (Secale cereale) It is another member of the grass family. A cereal grain originally from Asia that is mostly used to feed cattle. Rye flour is suitable for making bread, as it is the only cereal other than wheat containing gluten.The dough produced from rye flour has a sticky dense consistency and it keeps for a longer time, as it dries out more slowly. The bread is dark in color and close in texture. MILLETS: It is known as poor man’s cereal. Millets are a major food source in arid and semi- arid parts of the world. Used as forage and as a food for both man and domestic animals.More important in the East than West. 1. Foxtail millets (Setaria italica): Grown in Japan, China, and India – grains are boiled and eaten. In North America - mainly used as a forage crop 2. Proso millet (Panicum miliaceum) – Contains 10 % proteins, 4 % Fat: palatable bread can be made from these 3. Finger millet (Eleusine coracana): Ragi is grown mainly in the tropics. One of the most important cereal crop in china and Sri Lanka and India. 4. Sorghum (Sorghum vulgare): Staple food in drier part of tropical Africa, china, India. Native home is Africa. The grains are differently colored – Yellow, Red, or Brown Millets are good sources of energy. They provide protein, fatty acids, minerals, vitamins, dietary fiber and polyphenols. Typical millet protein contains high quantity of essential amino acids especially the sulphur containing amino acids (methionine and cysteine). Processing millet by milling removes the bran and germ layers that are rich in fiber and phytochemicals, causing significant loss. The millets are source of antioxidants, such as phenolic acids and glycated flavonoids. Millet foods are characterized to be potential prebiotic and can enhance the viability or functionality of probiotics with significant health benefits. Sorghum (Sorghum bicolor L.) jowar is a major source of energy and protein in developing countries, especially in Africa and Asia. Composition: The embryo is rich in protein, lipid, minerals and B-vitamin groups. Ragi: is also known as finger millet. It’s widely consumed practically without any refining by the poorer section of the population. Nutritionally it is almost as good as or better than wheat or rice.The major proteins of ragi are prolamins and glutelins and they appear to be adequate in all the essential amino acids. Ragi is rich in minerals especially calcium. It is also rich in fiber. It is high in phytate and Tannins hence interferes with availability of minerals.It contains B-Vitamins but is poor in B2.Refining the grains can upgrade the quality and adds variety and enhances the taste. Bajra: Among millets, bajra is the predominant crop in India. It has the same quantity of protein as wheat. Bajra is rich in Iron, thiamine, riboflavin and niacin. LEGUMES OR PULSES Beans, peas, lentils, groundnuts and their like belong to the botanical family of Leguminosae. Their edible seeds are called legumes or pulses. Agriculturally the plants of this group have the advantage of being able to obtain nitrogen from the air and also add some to the soil. Legumes have played an important role in the traditional diets of many regions throughout the world. It is difficult to think of the cuisines of Asia, India, South America, the Middle East, and Mexico without picturing soybeans, lentils, black beans, chickpeas, and pinto beans, respectively. In contrast, in many Western countries beans play a less significant dietary role. In fact, bean intake has actually declined during the past century in many European countries Lentils and some similar legumes often known as grams are very important in the diets of people in many developing countries Nutritive value: These legumes (excluding soybean) all have a somewhat similar nutritive value. The legumes are very important from a nutritional point of view because they are a widely available vegetable food containing good quantities of protein and B vitamins in addition to carbohydrate. Pulses give 340 calories per 100g which is almost similar to cereal calorie value. Proteins: Most legumes contain more protein than meat, most legume seeds usually contain about 22 percent protein but the protein is of slightly lower quality because it has less sulphur containing amino acids particularly methionine and tryptophan. Pulse proteins are chiefly globulins. However, they usually supplement very well the predominantly carbohydrate diet based on cereals. When pulses and cereals are eaten together at one meal they supply a protein mixture containing good quantities of all the amino acids, which improves the protein value of the diet. There are also a number of factors which reduce the nutritional value of pulse proteins, majority of pulse proteins have high molecular weights and are very compact molecules, and this reduces the digestibility of the native protein. Some proteins are found complexed* with carbohydrates and the carbohydrate moiety has a negative influence on the digestibility of the native protein. Proteins also form complexes with phytin and polyphenols present in pulses, contributing to their low digestibility. Carbohydrates: pulses contain 55 to 60 % starch. Soluble sugars, fiber and unavailable carbohydrates are also present.The sugars in pulses include substantial levels of oligosaccharides of the raffinose family (raffinose, verbascose and stachyose) which produces flatulence in man. These sugars escape digestion due to lack of the enzyme alpha-galactosidase activity and digested by the micro flora of the lower intestinal tract resulting in the production of large amount of carbon dioxide, hydrogen and small amounts of methane. Fermentation, germination, cooking, soaking and autoclaving reduce considerable amounts of the oligosaccharides. Lipids: pulses contain 1.5% of lipids. They contain high amounts of polyunsaturated fatty acids. Along with cereals they meet the essential fatty acid requirement of the adults. Mineral: They contain calcium, magnesium, zinc, iron, potassium and phosphorous.80% of the phosphorous is in the form of phytate phosphorous or phytin. Phytin complexes with protein and minerals and renders them unavailable to human beings and animals. Cooking, soaking, germination and fermentation can reduce or eliminate substantial amounts of phytin. Vitamins: Legumes also contain some carotene (provitamin A) and ascorbic acid if eaten green. Legume seeds are excellent source of B-Complex vitamins particularly thiamine, niacin, folic acid and pantothenic acid. Like cereals they do not contain any vitamin A or C but germinated legumes contain some vitamin C. ANTINUTRIENTS AND TOXIC COMPONENTS: LEGUMES Enzyme Inhibitors: Protease and amylase inhibitors are widely occurring in seed tissues including cereal grains. Trypsin, chymotrypsin, and cysteine-protease inhibitors are present in almost all pulses, although the individual inhibitor amounts are quite variable and are concentrated in the seed coat. They are believed to cause growth inhibition by interfering with digestion, causing pancreatic hypertrophy and metabolic disturbance of sulfur amino acid utilization.Trypsin inhibitor, chymotrypsin inhibitor, and amylase inhibitor levels are reduced during fermentation. These substances reduce protein digestion. They decompose with heat. Therefore, when legumes are eaten raw or without being cooked properly, they upset digestive functions and cause diarrhea or excessive gas. Autoclave treatment or boiling also reduces the quantity of these substances. The availability of amino acids (methionine and cystine) consisting of sulphur in legume grains is low. Amylase inhibitors alter reactions to blood sugar and insulin by slowing down digestion and thus can be used for therapeutic purposes in diabetes. Lectins (Hemagglutenins): All of them are proteins or glycoproteins. Lectin activity has been determined in more than 800 varieties of the legume family.2-10 % of the total protein legume seeds are lectins. One of their most important characteristics is that they prevent absorption of digestive end products in the small intestine. They enable the coagulation of red blood cells by affecting erythrocytes. Lectins possess some other interesting chemical and biological properties, some of which are as follows: they interact with specific blood groups; they perform various functions in mitotic division, demolish cancerous cells and have toxic effects in some animals. Oligosaccharides: They are gas generating factors in legumes. Legume seeds, which produce digestive gases in humans and animals, contain oligosaccharides of raffinose, stachyose and verbascose. As the duration of cooking increases, a decrease is observed in oligosaccharide content. Moreover, a decrease in oligosaccharide content also occurs when soaking water is poured, seeds are washed a second time or seeds are germinated. It is known that these flatulent substances, which belong to the indigestible fibers group, reduce the risk of intestinal cancer, fortifies the immune system, increases excretion frequency and weight as well as H DL cholesterol level. Saponins: They are glycoside derivatives that are found in many plants. Their general characteristics can be cited as follows: they give a bitter taste, foam when they are treated with various solutions and cause hemolysis in red blood cells. Since they reduce the surface tension of blood in cold-blooded animals, they have an extremely toxic effect. On the other hand, due to their cholesterol-reducing effect, legumes are the most important sources of saponins. The fact that saponins can bond with cholesterol and therefore reduce absorption and that legumes contain saponins points to their importance for health. Studies on medical uses of saponins continue. Cyanogenic Glycosides (HCN): Many members of the plant kingdom contain cyanide. Cyanogens compounds of tall plants are of two types: cyanogens glycosides and cyanogens lipids. Both groups contain cyanohydrins and free carbonyl. Since glycosides, which consist of HCN (hydrocyanic acid), can come out as a result of hydrolysis, they are potentially toxic. Cyanide cannot be disintegrated with heat and since it separates from legumes during cooking or washing, it will be beneficial to throw away soaking water. It is known that broad beans and Lima beans are potential sources of cyanide. Vicine and Convicine (Favism factors): Favism is a hemolytic disease that is found in sensitive individuals with consumption of broad beans. It is more widely found in people living in the Mediterranean countries. It is known to be of genetic source.The structure of hemoglobin, which is the primary carrier of oxygen, is upset. Dizziness, vomiting, feeling of tiredness and dark orange urine, which is the first symptom of blood transfusion, are symptoms of this disease. The disease disappears soon but incidences of death may be encountered when the disease is prolonged. This disease of hemolytic anemia is caused by favogens. Favism also causes high fever and jaundice. Phytic acid and phytates: Phytate phosphorous accounts for almost 80 % of the total phosphorous in many legume seeds.Phytic acid causes the bioavailability of essential minerals to decrease and turn into insoluble compounds whose absorption and digestion is less in the small intestine Pulses are sources of dietary Phytates. A way of preventing this is through the hydrolysis of phytate phosphorous; methods such as soaking, germinating, ,storing, methods like cooking and autoclaving where phytate phosphorous is destroyed in the presence of heat can also be used. Various studies that have been conducted demonstrated that phytate reduce cholesterol level and protect against intestinal cancer. Besides, phytate exhibit characteristics of natural antioxidants. Moreover, pulses are important sources of calcium, copper, iron, magnesium, phosphor, potassium and zinc. The content of these minerals and their bio-availability depend, to a large extent, on the degree of the processing (cooking) process and their absorption is affected. 50-80 % of the phytate in broad beans can be reduced through soaking and cooking. Goitrogens: Soybean, an oil seed, contains glycosides called goitrogens. Consisting of sulphur, these glycosides cause the thyroid gland to grow by inhibiting the iodine intake of the thyroid gland. This toxic effect can be reduced with the addition of iodine to the diet. Allergens: They are substances that are generally found in nutrients. They cause allergic reactions that are specific to certain individuals. The level of harm done depends on the sensitivity level of individual’s body rather than the quantity of the substances taken with the food. Diarrhea and vomiting are symptoms of allergy. It is also argued that proteins with high molecular weight cause allergies. Histamine and compounds of histamine derivatives act as antigens against allergens. Soaking, heating, fermentation can reduce or eliminate most of the toxic factors of the pulses. Intensity of the heat applied determines the extent of elimination. Cooking also contributes towards improvement in pulse digestibility.