28 TABLE 14.3 Amino Acid Content of Cereal Grains*(g amino acid/16 g nitrogen, Whea Triticale Rye Barley Rice Essential 8 6.0 7.2 8.0 Phenylalanine 5.2 3. 3.3 3.3 4.1 1.6 on-essential 2.6 3.0 6.6 Aspartic acid 345 30.9 27 20,4 5.0 12.1 14.5 17,9 Amino acid Millets Maize rl foxtail 4.0 3.8 6.1 Leucine 2508 0.8 3125315 Cysteine/cystine 5 4 10 4.0 Alanin 3136 6 2.3 Aspartic acid 18.8 21.7 3.9 2.3 l.2 2.1 13.5 12.4 2.5 Data for wheat, barley, oats, rye, triticale and pearl millet from Tkachuk a (1969); data for rice ano et al.(1964); data fe Dfrom bus erger(1965); data for foxtail and proso m Casey 1977); tryptophan data from Hughes(1967). All data are for whe except oats hulled and rye dark rye t Nx 5.7, d b Original data for maize and sorghum given as n x 6.25, viz. 11.6% and 11.5% respectively
NUTRITION 281 TABLE 14.3 Amino Acid Content of Cereal Grains* (g amino acid116 g nitrogen) Amino acid Wheat Triticale Rye Barley Oats Rice Essential Isoleucine 3.8 4.1 3.6 3.8 4.2 3.9 Leucine 6.7 6.7 6.0 6.9 7.2 8.0 Methionine 1.7 1.9 1.2 1.6 1.8 2.4 Phenylalanine 4.8 4.8 4.5 5.1 4.9 5.2 Threonine 2.8 3.1 3.3 3.5 3.3 4.1 Tryptophan 1.5 1.6 1.2 1.4 1.6 1.4 Valine 4.4 5.0 4.9 5.4 5.6 5.7 Cysteinelcy stine 2.6 2.8 2.3 2.5 3.3 1.1 Tyrosine 2.7 2.3 1.9 2.5 3.0 3.3 Arginine 4.0 4.9 4.2 4.4 6.6 7.7 Lysine 2.3 3.0 2.9 3.5 3.7 3.7 Non-essential Alanine 3.3 3.6 3.7 4.1 4.6 6.0 Aspartic acid 4.7 5.9 6.5 6.1 7.8 10.4 Glutamic acid 33.1 30.9 27.5 24.5 21.0 20.4 Glycine 3.7 3.9 3.6 4.2 4.8 5.0 Histidine 2.2 2.5 2.1 2.1 2.2 2.3 Proline 11.1 10.7 10.4 10.9 4.7 4.8 Serine 5.0 4.6 4.3 4.2 4.8 5.2 Protein? 16.3 12.1 17.8 14.5 17.9 11.1 Amino acid Millets Maize Sorghum pearl foxtail proso Essential Isoleucine 4.0 3.8 4.3 6.1 4.1 Leucine 12.5 13.6 13.1 10.5 12.2 Lysine 3.0 2.0 1.7 0.7 1.5 Methionine 1.8 1.5 2.4 2.4 2.2 Phenylalanine 5.1 4.9 5.6 4.2 5.5 Threonine 3.6 3.1 3.1 2.7 3.0 Tryptophan 0.8 1.c 1.4 2.0 0.8 Valine 5.2 5.0 5.4 4.5 5.4 Cysteineicystine 2.5 1.1 1.8 1.4 1.0 Non-essential Tyrosine 4.4 1.5 3.7 1.6 4.0 Alanine 7.7 9.5 11.3 Arginine 4.7 2.6 3.3 2.3 3.2 Aspartic acid 6.4 6.3 6.4 Glutamic acid 18.8 21.7 22.2 Glycine 3.9 3.1 2.3 Histidine 2.8 2.1 2.3 1.2 2.1 Proline 8.8 7.9 6.9 Serine 4.9 4.3 6.9 Protein? 10.6 10.5 13.5 12.4 12.5 * Data for wheat, barley, oats, rye, triticale and pearl millet from Tkachuk and Irvine (1969); data for rice (except tryptophan) from Juliano et al. (1964); data for maize (except tryptophan) from Busson et al. (1966); data for sorghum from Deyoe and Shellenberger (1965); data for foxtail and proso millets from Casey and Lorenz (1977); tryptophan data for rice and maize calculated from Hughes (1967). All data are for whole grains, except oats and rice - hulled grains - and rye - dark rye flour, ash 1.1% d.b. t Nx 5.7, d.b. Original data for maize and sorghum given as N X 6.25, viz. 11.6% and 11.S0/o respectively
TECHNOLOGY OF CEREALS different types of fibre; pentosans of different fats, include lauric, myristic (14: 0)and palmitic types of rice even vary in their effectiveness and (16: 0)acids- the three which have been impli their'preferredbile acids(Normandet al 1981). cated in raising the levels of cholesterol in blood It has been found that eating bran is an effective Palmitic acid (16: 0) is the most nly cure for constipation and diverticular disease. It is ring fatty acid comprising 35% of animal fats more doubtful whether dietary fibre is as effective and palm oil, and 17% of other plant oils and in preventing problems other than constipation. fish oils. The most commonly occurring mono- An important factor, though not the only one, unsaturated fatty acid is oleic acid(18: 1),it contributing to the beneficial effects of bran is its contributes 30-65% of most fats and oils. all ability to hold water, thus increasing stool weight cereal grain lipids are rich in unsaturated fatty and colonic motility. The relative water-holding acids(see Table 14.5) capacities of cereal brans and other sources of Palmitic(16: 0)is a major saturated, and linoleic fibre, given by Ory(1991)are shown in Table 14.4. (18: 2)a major unsaturated fatty acid in most cereals, exceptions being brown rice and oats Water-holding Capacity of Cereal Brans and Other Fibre- which are rich in oleic acid(18: 1). Millets are richer in stearic acid(18: 0)than are other cereals Fibre source No plant oils contain cholesterol Two advantages of rice bran oil are the low g/100g dm content of linolenic acid and its high content of Sugar beet pulp tocopherols, both important from the point of view Apple pomace 235-509 of oxidative stability. Its high content of linoleic Apple, whole fruit acid makes it a good source of essential fatty acid All bran Wheat bran 109290 Oat groats contain 7% oil, pearl millet 5.4% Rice bran maize 4. 4%, sorghum 3. 4%, brown rice 2.3% Maize bran barley 2. 1% and wheat 1.9% The hard, high-melting fraction of rice bran wax has lustre-producing qualities similar to 3367 hose of carnauba wax. It has been approved by Orange pulp the u.s. Food and Drug Administration as a ole vegetable constituent of food articles up to 50 mg/kg and for use as a plastisizer for chewing gum at 2% Potato, minus skin juliano, 1985b) Sources: Gormley, 1977; Hetler and Hackler, 1977(their Maize germ oil is rich in essential fatty acids values are reported as, for fresh weight basis ); and (about half of its fatty acid content is linoleic).It Chen et aL., 1984. Reprinted with permission from Ory, R L, 1991. Copyright, 1991, American Chemical Society is used as a salad oil and for cooking ts Minerals Apart from essential fatty acids, the liver is At least 15 minerals are required by humans able to make all the fat that the body requires Of these, deficiencies are unlikely to occur in from carbohydrates and protein, provided these phosphorus, sodium, chlorine or potassium,even are eaten in sufficient quantities. About 10 g of though daily requirements are relatively high essential fatty acids are needed every day by Anaemia, due to iron deficiency, is one of the most the human body, but in the U. K. the average common nutritional disorders, particularly in consumption is 10-fold this pre-menopause women. Iron from exhausted red Nearly all the fat in the diet is composed of blood cells is re-used in new cells, so that almost triacylglycerols (triglycerides). Saturated fatty the only requirement is to replace blood that has acids, found mainly in animal fats and hardened been lost Wholegrain cereals contain sufficient
282 TECHNOLOGY OF CEREALS different types of fibre; pentosans of different types of rice even vary in their effectiveness and their ‘preferred’ bile acids (Normand et al., 198 1). It has been found that eating bran is an effective cure for constipation and diverticular disease. It is more doubtful whether dietary fibre is as effective in preventing problems other than constipation. An important factor, though not the only one, contributing to the beneficial effects of bran is its ability to hold water, thus increasing stool weight and colonic motility. The relative water-holding capacities of cereal brans and other sources of fibre, given by Ory (1991) are shown in Table 14.4. TABLE 14.4 Containing Foods fats, include lauric, myristic (14:O) and palmitic (16:O) acids - the three which have been implicated in raising the levels of cholesterol in blood. Palmitic acid (16:O) is the most commonly occurring fatty acid, comprising 35% of animal fats and palm oil, and 17% of other plant oils and fish oils. The most commonly occurring monounsaturated fatty acid is oleic acid (18:1), it contributes 3045% of most fats and oils. All cereal grain lipids are rich in unsaturated fatty acids (see Table 14.5). Palmitic (16:O) is a major saturated, and linoleic (18:2) a major unsaturated fatty acid in most cereals, exceptions being brown rice and oats richer in stearic acid (18:O) than are other cereals. No plant oils contain cholesterol. Two advantages of rice bran oil are the low content of linolenic acid and its high content of tocopherols, both important from the point of view Sugar beet pulp Apple pomace of oxidative stability. Its high content of linoleic Apple, whole fruit acid makes it a good source of essential fatty acid. Oat groats contain 7% oil, pearl millet 5.4%, All bran 436 Wheat bran 109-290 Rice bran 131 maize 4.4%, sorghum 3.4%, brown rice 2.3%, Oat bran 66 barley 2.1% and wheat 1.9%. The hard, high-melting fraction of rice bran Maize bran 34 Cauliflower 28 Lettuce 36 wax has lustre-producing qualities similar to Carrot 33-67 those of carnauba wax. It has been approved by the U.S. Food and Drug Administration as a Orange, whole fruit 20-56 Orange pulp 176 Onion, whole vegetable 14 constituent of food articles up to 50 mg/kg and Banana, whole fruit 56 for use as a plastisizer for chewing gum at 2%. (Juliano, 1985b) Potato, minus skin 22 Maize germ oil is rich in essential fatty acids (about half of its fatty acid COntent is linoleic). It is used as a salad oil and for cooking. Water-holding Capacity of Cereal Brans and Other Fibre- which are rich in oleic acid (18: 1). Millets are Fibre source Water-holding capacity. g/lOOg d.m. 1449 235-509 17-46 Sources: Gormley, 1977; Hetler and Hackler, 1977 (their values are reported as ‘corrected’ for fresh weight basis); and Chen et al., 1984. Reprinted with permission from Ory, R. L., 1991. Copyright, 1991, American Chemical Society. Fats Minerals Apart from essential fatty acids, the liver is able to make all the fat that the body requires from carbohydrates and protein, provided these are eaten in sufficient quantities. About 10 g of essential fatty acids are needed every day by the human body, but in the U.K. the average consumption is 10-fold this. Nearly all the fat in the diet is composed of triacylglycerols (triglycerides). Saturated fatty acids, found mainly in animal fats and hardened At least 15 minerals are required by humans. Of these, deficiencies are unlikely to occur in phosphorus, sodium, chlorine or potassium, even though daily requirements are relatively high. Anaemia, due to iron deficiency, is one of the most common nutritional disorders, particularly in pre-menopause women. Iron from exhausted red blood cells is re-used in new cells, so that almost the only requirement is to replace blood that has been lost. Wholegrain cereals contain sufficient
83 TABLE 14.5 The Fatty Acid Composition of Cereal lipids* Saturated Unsaturated Material myristic Oleic 12.6 33.1 23.1 52.3 pear 178 .7 23.9 3.0 foxtail 11.0 4.7 11.5 43.5 808 21.0 61.0 13.2 18.7 24.5 11.5 3 18.5 0.4 17,3 endosperm 18.0 1.2 194 56.2 3.1 Source: Kent(1983 iron to supply a large proportion of an adults wholemeal might seem illogical(since wholemeal daily requirement, but there is some doubt as to of all types of four contains the largest amount of whether it can be absorbed from cereal and phytic acid, and would seem to require the largest legume sources because of the presence of phytic addition of chalk), it must be remembered that acid. About 900 mg of calcium are present in the consumers of this particular product are concerned average U. K. diet, and of this, 25% is supplied to an exceptional extent with the concept of absence by cereals. Growing children and pregnant and of all additions lactating mothers have a higher requirement of Bran and wheat germ are good sources of about 1200 mg per day. The aged hay with other minerals, absorpti enhanced requirement for calcium as it may be can be impaired by the phytate also present depleted by insufficient vitamin D. Adequate In addition to the above, the following elements calcium consumed during growth affords some are require the body, but in much smaller protection against osteoporosis in later years. a traceamounts: iodine, copper zinc, manganese, further protective function served by adequate molybdenum, selenium and chromium and even isotope strontium 90(S70), produced as part of fluorine may be needed on, tin, nickel, arsenic and calcium in the diet concerns the radioactive smaller quantities of silic the fall-out of nuclear explosions, which can arise Wholegrain cereals can contribute to the supply from weapons or accidents in nuclear power of zinc, although its absorption might be impaired stations. Sr%0 can replace calcium in bones, causing by phytic acid. The selenium content of grain irritation and disease, but in the presence of high depends upon the selenium status of the soil on calcium levels this is less likely. Flours, other which the crop was grown. In North America than wholemeal, malt flours and self-raising many selenium-rich soils support cereals, and fours (which are deemed to contain sufficient wheat imported from that continent has relatively calcium), are required to be supplemented with large amounts present, enabling half the daily chalk (calcium carbonate) in the U. K. but it is requirement to be met from cereals. Soils in the doubtful if this is necessary. If the exception of U.K. have less selenium and hence the grains
NUTRITION 283 TABLE 14.5 The Fatty Acid Composition of Cereal Lipids* Saturated Unsaturated Material Myristic Palmitic Stearic Oleic Linoleic Linolenic c14.0 c16.0 C18.0 CIS., CIS2 Cl8.3 (“h) (%) (%) (%) (“h) (%) Barley 6-row 3.3 7.7 12.6 19.9 33.1 23.1 2-row 1.0 11.5 3.1 28.0 52.3 4.1 Maize - 14.0 2.0 33.4 49.8 1.5 Millet pearl - 17.8 4.7 23.9 50.1 3.0 foxtail 0.6 11.0 14.7 21.8 38.2 6.4 11.5 - 25.8 50.6 7.8 proso - Oats 0.5 15.5 2.0 43.5 35.5 2.0 Rice - 17.6 47.6 34.0 0.8 Rye - 21.0 - 18.0 61.0 - Sorghum 0.4 13.2 2.0 30.5 49.7 2.0 Triticale 0.7 18.7 0.9 11.5 61.2 6.2 Wheat grain 0.1 24.5 1 .o 11.5 56.3 3.7 germ - 18.5 0.4 17.3 57.0 5.2 endosperm - 18.0 1.2 19.4 56.2 3.1 * Source: Kent (1983). iron to supply a large proportion of an adult’s daily requirement, but there is some doubt as to whether it can be absorbed from cereal and legume sources because of the presence of phytic acid. About 900 mg of calcium are present in the average U.K. diet, and of this, 25% is supplied by cereals. Growing children and pregnant and lactating mothers have a higher requirement of about 1200 mg per day. The aged have an enhanced requirement for calcium as it may be depleted by insufficient vitamin D. Adequate calcium consumed during growth affords some protection against osteoporosis in later years. A further protective function served by adequate calcium in the diet concerns the radioactive isotope strontium 90 (Sr9’), produced as part of the fall-out of nuclear explosions, which can arise from weapons or accidents in nuclear power stations. Sr90 can replace calcium in bones, causing irritation and disease, but in the presence of high calcium levels this is less likely. Flours, other than wholemeals, malt flours and self-raising flours (which are deemed to contain sufficient calcium), are required to be supplemented with chalk (calcium carbonate) in the U.K. but it is doubtful if this is necessary. If the exception of wholemeal might seem illogical (since wholemeal, of all types of flour contains the largest amount of phytic acid, and would seem to require the largest addition of chalk), it must be remembered that consumers of this particular product are concerned to an exceptional extent with the concept of absence of all additions. Bran and wheat germ are good sources of magnesium but, as with other minerals, absorption can be impaired by the phytate also present. In addition to the above, the following elements are required by the body, but in much smaller ‘trace’ amounts: iodine, copper, zinc, manganese, molybdenum, selenium and chromium and even smaller quantities of silicon, tin, nickel, arsenic and fluorine may be needed. Wholegrain cereals can contribute to the supply of zinc, although its absorption might be impaired by phytic acid. The selenium content of grain depends upon the selenium status of the soil on which the crop was grown. In North America many selenium-rich soils support cereals, and wheat imported from that continent has relatively large amounts present, enabling half the daily requirement to be met from cereals. Soils in the U.K. have less selenium and hence the grains
TECHNOLOGY OF CEREALS produced on them are poorer in the element. and vitamin E, that are most important in cereal Symptoms of selenium deficiency have been grains. The average contents of B-vitamins are reported in countries with notably deficient soils, shown in Table 14.7 cluding New Zealand and some areas of china The table also includes values for inositol The mineral composition of cereal grains is and p-amino-benzoic acid Although essential shown in table 3. 6 for some micro-organisms, these substances are no longer considered essential for humans. Their status as vitamins is thus dubious, Choline and inositol are by far the most abundant but cereals Vitamins comprise a diverse group of organic are not an important source as many foods compounds. They are necessary for growth and contain them and deficiencies are rare(Bingham, metabolism in the human body, which is incapable 1987) of making them in sufficient quantities to meet its needs, hence the diet must supply them to Distribution of vitamins in cerea/s aintain good health. Most vitamins are known today by their chemical descriptions, rather than variation in content from one cereal to another the earlier identification as vitamin A, B, c etc. is remarkably small except for niacin (nico- a table of equivalence relates the two methods tinic acid), the concentration of which is rela of nomenclature(Table 14.6). Those in bold tively much higher in barley, wheat, sorghum type occur in cereals in significant quantities(in and rice, than in oats, rye, maize and th relation to daily requirements) Details of the distribution in grains were worked TABLE 14.6 out by Hinton and his associates, who assayed the Vitamins and their Occurrence in Cereals dissected morphological parts of wheat, maize Vitamin Chemical Name Concentration in cereals and rice. Their results for wheat are shown in Table 14. 8 Retinol and Carotene Thiamin Embryo(scutellum The distribution of these vitamins in the wheat Riboflavin Most parts grain is also shown diagrammatically in Fig 14.3 Nicotinic acid(niacin) Aleurone(not maize The proportions of total thiamin and niacin are shown for rice and maize in Table 14.9 Pantothenic acid Aleurone, endosperm The distributions of thiamin in rice and wheat are quite similar: it is concentrated in the scutel Carnitine lum, though not to the same degree as in rye and Cholicalciferol and maize. The embryonic axis of rice, which has a relatively high concentration of thiamin, contains E Tocopherol and tocotrienol Embryo over one tenth of the total in the grain, a larger K Phyllo qUinone proportion than that found in the other cereals (see Table 14.10 Vitamins are sometimes classified according to Cereals, except maize, contain tryptophan, which solubility; thus A, D, E and K are fat soluble, can be converted to niacin in the liver in the and B and C are water soluble. Fat soluble presence of sufficient thiamin, riboflavin and vitamins are the more stable to cooking and pyridoxin. The distributions of in wheat, processing. rice and maize are similar, it is concentrated in It is clear from Table 14.6 that it is the b the aleurone layer. About 80% of the niacin itamins(more specifically thiamin, riboflavin, in the bran of cereals occurs as niacytin, a com- pyridoxine nicotinic acid and pantothenic acid) plex of polysaccharide and polypeptide moieties
284 TECHNOLOGY OF CEREALS produced on them are poorer in the element. Symptoms of selenium deficiency have been reported in countries with notably deficient soils, including New Zealand and some areas of China. The mineral composition of cereal grains is shown in Table 3.6. Vitam ins Vitamins comprise a diverse group of organic compounds. They are necessary for growth and metabolism in the human body, which is incapable of making them in sufficient quantities to meet its needs, hence the diet must supply them to maintain good health. Most vitamins are known today by their chemical descriptions, rather than the earlier identification as vitamin A, By C etc. A table of equivalence relates the two methods of nomenclature (Table 14.6). Those in bold type occur in cereals in significant quantities (in relation to daily requirements). millets. and vitamin E, that are most important in cereal grains. The average contents of B-vitamins are shown in Table 14.7. The table also includes values for inositol and p-amino-benzoic acid. Although essential for some micro-organisms, these substances are no longer considered essential for humans. Their status as vitamins is thus dubious. Choline and inositol are by far the most abundant but cereals are not an important source as many foods contain them and deficiencies are rare (Bingham, 1987). Distrjbution of vitamins in cerea,s Variation in content from one cereal to another is remarkably small except for niacin (nicotinic acid), the concentration of which is relatively much higher in barley, wheat, sorghum and rice, than in oats, rye, maize and the Details of the distribution in grains were worked out by Hinton and his associates, who assayed the dissected morphological parts of wheat, maize Vitamin Chemical Name Concentration in cereals and rice. Their results for wheat are shown in Table 14.8. A Retinol and Carotene The distribution of these vitamins in the wheat B1 B2 Riboflavin Most parts grain is also shown diagrammatically in Fig. 14.3. B6 Pyridoxin Aleurone Bl2 Nicotinic acid (niacin) Aleurone (not maize) The proportions of total thiamin and niacin are Folic acid shown for rice and maize in Table 14.9. Biotin Pantothenic acid Aleurone, endosperm The distributions of thiamin in rice and wheat Choline are quite similar: it is concentrated in the scutellum, though not to the same degree as in rye and Carnitine C Ascorbic acid D Cholicalciferol and maize. The embryonic axis of rice, which has a ergocalciferol relatively high concentration of thiamin, contains Tocopherol and over one tenth of the total in the grain, a larger E tocotrienol Embryo K Phylloquinone proportion than that found in the other cereals (see Table 14.10). Cereals, except maize, contain @pt@hn~ which can be converted to niacin in the liver in the presence of sufficient thiamin, riboflavin and pyridoxin. The distributions of niacin in wheat, rice and maize are similar, it is concentrated in the aleurone layer. About 80% of the niacin in the bran of cereals occurs as niacytin, a complex of polysaccharide and polypeptide moieties TABLE 14.6 Vitamins and their Occurrence in Cereals Thiamin Embryo (scutellum) Vitamins are sometimes classified according to solubility; thus A, D, E and K are fat soluble, and B and c are water soluble. Fat soluble vitamins are the more stable to cooking and processing. It is clear from Table 14.6 that it is the B vitamins (more specifically thiamin, riboflavin, pyridoxine nicotinic acid and pantothenic acid)