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14 Nutrition Introduction elements. Also cereal proteins are deficient in certain essential amino acids, notably lysine. Cereals however are rarely consumed alone, and ally compensate for each other¡¯s deficiencies. While it is indisputable that individuals and populations should consume the right amounts of nutrients to avoid symptoms of deficiency and excess, defining those ¡®right amounts¡¯ is not easy, not least because the requirements vary from one individual to another. The British Government, for more than 30 years issued standards in the form of Recommended Intakes fm Nutrients (DHSS, 1969) and Recommended Daily Amounts (RDA) of food energy and nutrients (DHSS, 1979). In revising the recommendations for the dietary requirements of the nation, the Committee on Medical Aspects of Food Policy (COMA), noted that was never intended, that is they were used to aSSeSS the adequacy of the diets of individuals. In order to ensure that deficiencies were avoided the RDAs represented at least the minimum requirements of those individuals with the greatest need. In terms of the population as a whole, therefore, they were overestimates, and indivi- duals ingesting less than the RDA for any nutrient may be far from deficient. Instead of revized RDAs, Dietary Reference Values (DRV) for Food Energy and Nutrient for the United Kingdom (DH, 1991) were issued. They applied to energy, proteins, fats, sugars, starches, non-starch poly- saccharides, 13 vitamins and 15 minerals, and they comprised: Estimated Average Requirement (EAR) - an Nutrition in most adults is concerned with the the diet needed to maintain normal functioning of the body (water and oxygen are also necessary but these are not generally regarded as nutrients). In the young and in pregnant and lactating mothers additional nutritional requirements are imposed by the need to support growth or milk production. Nutrients - the substances that provide energy and raw materials for the synthesis and main- tenance of living matter, in the diet of humans and other animals, comprise protein, carbohydrate, fat, all of which can provide energy, minerals and vitamins. Those nutrients that cannot be made in sufficient quantities by conversion of other include some vitamins, minerals, essential amino acids and essential fatty acids. An insufficiency of an essential nutrient causes a specific deficiency disease. Deficiency diseases are now rare in the West where food is plentiful, but they remain a problem in the Third world, where natural disasters and conflict frequently lead to malnutrition and even starvation. Aid provided for the relief of such disasters always includes a high proportion of cereals, demonstrating their high nutritional value. Although cereals make an important contribu- tion to the diet they cannot alone support life because they are lacking in vitamins A (except for yellow maize), BIZ and C. Whole cereals also contain phytic acid, which may interfere with the absorption of iron, calcium and some trace suPP1Y and metabo1ism Of those components Of nutrients in foods consumed together, may mutu- nutrients in the bodyY are ca11ed essentia1* They that the standards were frequently used in a way 276 NUTRITION 277 excessive and should be avoided. So also should table salt and foods cooked or preserved in excessive salt. In the U.S.A. the USDAAJSDHHS published guidelines (1985) for a healthy diet including the following recommendations: Eat a variety of foods. Maintain desirable weight. Avoid too much fat, saturated fat and cholesterol. Eat foods with adequate starch and fibre. Avoid too much sugar. Avoid toO much sodium. If you drink alcoholic beverages, do so in moderation. Both U.K. and U.S. recommendations acknow- ledge the importance of cereals, particularly as a source of energy and non-starch polysaccharides. In addition, however, cereals provide many other valuable nutrients, including proteins, vitamins and minerals as several of the tables and figures in this chapter demonstrate. estimate of the average requirement or need for food energy or a nutrient. Reference Nutrient Intake (RNI) - enough of a nutrient for almost evey individual, even someone who has high needs for the nutrient. Lower Reference Nutrient Intake (LRNI) - the amount of a nutrient that is enough for only a small number of people with low needs. Safe Intake - a term normally used to indicate the intake of a nutrient for which there is not enough information to estimate requirements. A safe intake is one which is judged to be adequate for almost everyone¡¯s needs but not so large as to cause undesirable effects. In recognition of the fact that people of different sexes, ages (e.g. infants, children, adults) and conditions (e.g. pregnant and lactating mothers) have different requirements, DRVs appropriate to the different groups were defined. Deficiency diseases, such as rickets, stunting, deformities and anaemia, are now rare in Western countries and, in considering the relationship between food and disease, emphasis has shifted to other diseases that are thought to be diet related: these include cancer of the colon (associ- For the majority of the world¡¯s human popula- ated with animal protein intake, particularly tion, cereal-based foods constitute the most meat), breast cancer (associated with fat intake), important source of energy and other nutrients. In and stroke and heart disease, associated with the poorest parts of the world starchy foods, consumption of salt and animal (saturated) fat including cereals, may supply 70% of total energy. (Bingham, 1987). In the wealthiest nations the proportion obtained from cereals has declined fairly rapidly: in the U.S.A. during the present century the proportion of total energy provided by cereals has dropped from 40% to between 20 and 25%. The propor- tions of some important nutrients derived from cereals and products in Britain are shown in Table 14.1. Positive attributes of cereals as foods Starc, Cereals are a particularly rich source of starch as it constitutes by far the most abundant storage product in the endosperm. Starch is an important More than 8Og per day for men and more than source of energy, it is found only in plants (although the related compound glycogen occurs in Cereals in the diet Recommendations Recommendations appropriate to the U.K. situation are that cereals, particularly whole grain, together with potatoes, should be eaten in generous amounts at each main meal to satisfy appetite, three or more portions of fresh vegetables or fruit, preferably green or yellow, should be eaten per day and two or more portions of low fat foods containing the most protein. Low fat daiy foods should be chosen in preference to high fat ones and all sugar, refined starches, and foods made from them, such as biscuits, cakes, sweets, etc. should be used sparingly. 50g per day for women, of alcohol is considered 278 TECHNOLOGY OF CEREALS TABLE 14.1 Contnbutwns (¡°h) Made by Cereal Products to tk Nurn¡¯tional Value of Household Food in Britain. 1990* Bread Cakes, Cereals White Brown and pastries, Breakfast wholemeal biscuits cereals Energy 31.5 7.2 3.4 8.2 3.4 Fat 12.8 1 .o 0.8 7.6 0.5 Fatty acids: Saturated 12.1 0.6 0.3 9.0 0.3 Polyunsaturated 13.7 2.2 1.4 5.0 1.4 Sugars 18.7 1.8 0.7 10.0 2.8 Starch 73.0 20.4 9.0 9.9 8.5 Fibre 45.5 7.4 11.6 5.0 9.9 Calcium 24.6 7.5 2.8 4.0 1 .o Iron 49.0 8.7 7.7 6.7 15.4 Sodium 38.3 12.6 6.5 5.0 5.4 - 1.0 Vitamin C 1.5 Vitamin A 1.1 - - 0.5 - Vitamin D 12.3 - - 1.3 9.6 - - * Values calculated from appendix B, Table 14, Household Food and Expenditure 1990 MAFF, HMSO, London, 1991. -_ - nil. Reproduced with the permission of the Controller of Her Majesty¡¯s Stationery Office. animal tissues). In the past, starch has been under- low and gelatinization takes place at an elevated valued by nutritionists, who have emphasized temperature. its association with obesity, and recommended Energy is released from starch by digestion of reduction in, for example, bread consumption by starch polymers to produce glucose, which is those wishing to control their weight. However, absorbed into the bloodstream. Glucose yields 16 starch is preferable, as an energy source, to fat, kilojoules or 4 kilocalories per gram (joules are now and a further advantage of starch consumed as the preferred unit in which to express energy, part of a cereal food is that it is accompanied 4.184 J = 1 cal). by vitamins, minerals and protein. In the best Starches from ¡®amylo¡¯ mutant types of cereals balanced diet starch would probably contribute (mainly maize), which have a higher than usual rather more than the 20% that it provides in the amylose content, are less readily digested. After average U.K. diet today (nearly 40% comes from cooking at high temperatures, the indigestibility fat, and 13% from sugar). The value of 31.5% may be enhanced, giving rise to a small propor- for energy contributed by cereals (Table 14.1) tion of resistant starch. Even in other cooked cereal refers only to foods consumed in the home. products some resistant starch can arise; it behaves Most starch is consumed in cooked products, like fibre, passing unchanged through the gut. in the majority of which the starch granules are The method of cooking is important in deter- gelatinized, making them readily digestible by mining the amount of resistant starch formed. In amylase enzymes pesent in the gut. For this to corn flakes produced by extrusion cooking the occur however, abundant water is required as proportion of resistant starch is less than in starch can absorb more than 20 times its own conventionally produced flakes (Ch. 11). mass during gelatinization. In some baked Energy is a vital requirement of every healthy products, such as shortbread, much fat and individual but energy that is not expended in little water are present; consequently few of the physical or physiological activity is stored either granules are gelatinized. Other factors, such as as adipose tissue or glycogen. These provide osmotic conditions, affect gelatinization, these a necessary store from which energy may be are much affected by the amount of sugar in the released when required. The superiority of starch recipe: in high sugar conditions water activity is as a dietary energy source does not derive from NUTRITION 279 a particularly high calorific value; in fact that of 20 fat is higher, at 37 kJ (9 kcal) per gram, as is 15 alcohol at 29 kJ (7 kcal) per gram than that of g starch. 25 Protein content and quality 0 Cereals including bread, contribute approxim- ately 25% of the protein in the average adult diet in the U.K. Three thin slices of bread contribute as much protein as an egg. In nutritional terms there are two factors of prime importance in relation to protein: the total protein content, and the contribution that essen- tial amino acids make to the total. There are eight essential amino acids (out of a total of 20 or so) - methionine, tryptophan, threonine, valine, isoleucine, leucine, phenylalanine and lysine. Two other amino acids are sometimes classified as essential but they can be made in the body - tyrosine from phenylalanine and cysteine/ cystine from methionine. Their presence in foods reduces the requirements Of the re1evant 'parent' essential amino acids. In foods derived from plants in general, the sulphur-containing amino acids methionine and cysteine are most likely to be limiting, but this is not true of cereal grains. In cereals, lysine is the first to be limiting: rice, oat and rye are relatively rich among wholegrain cereals but they are deficient in relation to the FAO/WHO (1973) reference amino acid pattern, in which the lysine content is 5.5 g/16 g of N. Maize protein is also limiting in tryptophan, based on the reference value of 1.0 g/16 g of N, which the other cereals just reach. A comparison between wheat 'rotein and 'rotein from Other food soLlrces is shown in Fig. 14.1. In the past, much was made of the superiority of animal-derived proreins, containing, as they do, the correct proportions of essential amino acids. However, protein types are rarely eaten alone and they tend to complement each other; for example, bread may be eaten with cheese, a good source of lysine. Even in vegetarian diets, many legumes and nuts supply essential amino acids. A good combination is rice and peas. Both content (Fig. 14.2) and composition of protein are affected by the contributions of different IO 0 2 25 20 - .$ - 5 l5 f 1o 5 0 FIG 14.1 The essential amino acids in food proteins. The relative proportions of each essential amino acid are shown expressed as the percentage of the total essential amino acids. From Coultate, 1989, by courtesy of The Royal Society of Chemistry. Protein FIG. 14.2 Distribution of total protein in the wheat grain. The figures show the percentage of the total protein found in the various anatomical parts. (Based on micro-dissections by J. J. C. Hinton. From The Research Association of Bntzsh Flour Millers 1923-60.) anatomical parts of the grain; and in the endo- sperm, by the contributions of the different protein fractions (albumins, globulins, prolamins, glutelins). The insoluble fractions are particularly deficient in lysine, as illustrated in the comparison of the solu- bility fractions of wheat endosperm (Table 14.2). 280 TECHNOLOGY OF CEREALS TABLE 14.2 within the last 20 or so, attention has been Amino Acid Composition of Wheat Proteins: Glutenin, Gliadin, focussed on them by the assertion that the high Albumin, Globulin (g amino acid116 g nitrogen) fibre of African diets prevents many chronic non- Amino acid Glutenin* Gliadin* Albumin+ Globulin* infective diseases common in the West, where refined carbohydrates are more commonly con- Isoleucine 3.9 4.5 4.1 1.4 Leucine 6.9 7.2 10.7 9.2 sumed. Some of the more extreme claims for the Lysine 2.3 0.7 11.0 12.2 beneficial effects of fibre, emanating from the surge of activity consequent upon these assertions Methionine 1.7 1.5 0 0.4 Phenylalanine 4.8 5.6 5.0 3.2 Threonine 3.3 2.3 2.9 4.5 have now been seriously challenged, as popula- Tryptophan 2.1 0.7 n.d. n.d. tions of Third-world states eating lower fibre diets but not showing high incidence of the relevant Valine 4.5 4.4 8.1 2.2 Cystine 2.5 3.1 6.7 12.6 Tyrosine 3.6 2.6 3.4 2.3 diseases have been discovered. Nevertheless, Alanine 3.1 2.3 5.6 4.3 dietary fibre has been shown to have palliative effects on diseases, particularly those of the gut Arginine 4.2 2.7 7.5 14.5 Aspartic acid 3.9 3.0 7.9 6.3 Glutamic acid 34.1 40.0 17.7 5.9 and diabetes mellitus. Glycine 4.5 1.8 3.1 5.6 Histidine 2.4 2.3 4.3 2.2 Proline 11.0 14.7 8.4 3.3 Ch o les te ro I Serine 5.9 5.1 4.7 9.1 This is much publicized as an indicator disease, strokes and blocked arteries, but it is not all bad. Some cholesterol is necessary in the body as a precursor of hormones and bile acids. Cholesterol is transported in the blood in three principal forms: free cholesterol or bound to Among samples of the same cereal, there lipoprotein as either High density lipoprotein (HDL), or Low density lipoprotein (LDL). HDL even confers some protection against heart disease, so reduction below a threshold actually increases risk. About 80% of blood cholesterol is associated with LDL, however, and it is this form which is believed to deposit in the arteries. It is also this form that increases as a result of consumption of saturated fats. Considerable reduction in blood cholesterol levels have been reported in response to increased cereal fibre in the diet. Several mechanisms have been proposed to account for the hypocholesterolaemic effect of soluble fibres: viscous soluble fibre may exert an effect by physically entrapping cholesterol or bile acids in the digestive tract, thereby preventing their absorption and resulting in their increased excre- tion. Alternatively, P-glucans may be fermented by colonic bacteria to short chain fatty acids. Several of these compounds have been suggested as inhibitors of cholesterol synthesis. In relation to the first possibility, it has been found that different bile acids are bound more effectively by * From Ewart (1967), recalculated. Original data are given as moles of anhydroamino acids per lo5 of recovered anhydro t From Waldshmidt-Leitz and Hochstrasse (1961). $ From Fisher et al. (1968). n.d. = not determined. Of potential hea1th problems, particularly heart amino acids. are considerable variations in protein content. Because there is a consistent relationship between protein content and the proportions of the frac- tions present, protein composition in whole grains also varies. Nevertheless, the differences among samples of the same cereal are generally less than differences among cereal species, and proteins characteristic of individual species can be des- cribed. It must however be remembered that values cited in comparisons are only at best averages, representing points within a range typical of the species. Values for the proportions of classified amino acids in whole grains of cereals are given in Table 14.3. Fibre The laxative properties of fibre or ¡®roughage¡¯, as it was previously picturesquely described, have been well known for many hundreds of years (Hippocrates advocated it around 400 B.C.!) but 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. 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 impli- cated in raising the levels of cholesterol in blood. Palmitic acid (16:O) is the most commonly occur- ring fatty acid, comprising 35% of animal fats and palm oil, and 17% of other plant oils and fish oils. The most commonly occurring mono- unsaturated 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 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 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 (nico- tinic acid), the concentration of which is rela- tively 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 scutel- lum, 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 com- plex 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) N UTRlTl ON 285 TABLE 14.7 B Vitamin Content of the Cereal Grains* (pgig) Cereal Thiamin Riboflavin Niacin Pantothenic Biotin acid Wheat 10 0.1 45 5.7 0.13 Barley 4.4 1.5 72 Oats (whole) 5.8 1.3 11 10 0.17 Rye 4.4 2.0 12 7.2 0.05 Triticale 9.2 3.1 16 7.5 0.06 Rice (brown) 3.3 0.7 46 9 0.1 Maize 4.0 1.1 19 5.3 0.1 Sorghum 3.5 1.4 41 11 0.19 Millet pearl 3.6 1.7 26 11.4 - foxtail 5.9 0.8 7 proso 2.0 1.8 23 finger 3.6 0.8 13 54 1 hard 4.3 1.3 soft 3.4 1.1 - - - - - - Cereal Pyridoxin Folic Choline Inostiol p- Amino Wheat hard soft acid benzoic acid ] 4.5 0.5 1100 2800 2.4 Barley 4.4 0.4 1000 2500 0.5 Oats (whole) 2.1 0.5 940 3.2 0.6 450 - - Rye Triticale 4.7 0.7 Rice (brown) 4.0 0.5 900 Maize 5.3 0.4 445 - - Sorghum 4.8 0.2 600 - - Millet - - - - - I - - - - - - pearl foxtail proso finger - - - - - * Sources of data are as quoted in Kent (1983). A dash indicates that reliable data have not been found. The above data are similar to those given by Holland et al. (1991) who provide comprehensive tables of vitamin contents - - - - - - - - - - of cereal products also. TABLE 14.8 Distribution of B Vitamins in the Wheat Grain.* Concentration in pgig and YO of total in parts Part of grain Thiamint Riboflavin$ Niacin$ Pyridoxin$ Pantothenic acid$ Concn. YO Concn. % Concn. YO Concn. YO Concn. YO wig Pdg Pgk Pgk Pgk Pericarp, testa, hyaline 0.6 1 1.0 5 25.7 4 6.0 12 7.8 9 Endosperm 0.13 3 0.7 32 8.5 12 0.3 6 3.9 43 Embryonic axis 8.4 2 13.8 12 38.5 1 21.1 9 17.1 3 Scutellum 156 62 12.7 14 38.2 1 23.2 12 14.1 4 Whole grain 3.75 1.8 59.3 4.3 7.8 Aleurone layer 16.5 32 10 37 741 82 36 61 45.1 41 * Sources of data: Clegg (1958); Clegg and Hinton (1958); Heathcote et al. (1952); Hinton (1947); Hinton et al. (1953) t Wheat variety Vilmorin 27. $ Wheat variety Thatcher. 286 TECHNOLOGY OF CEREALS Aneurine (vitamin B, 1 Nicotinic acid Aleurone layer Riboflavin Pantothenic acid Pyridoxin (vitamin B,) rone Embryo FIG. 14.3 Distribution of B vitamins in the wheat grain. The figures show the percentages of the total vitamins in the grain found in the various anatomical parts. (Based on micro-dissections by J. J. C. Hinton. From The Research Associatia of British Flour Millers 1923-60.) TABLE 14.9 Maize* biologically unavailable to man unless treated Riboflavin and pantothenic acid are more uni- formly distributed. Pyridoxin is concentrated in Percentage aleurone and other nonstarchy endosperm parts The uneven distribution of the B vitamins Part of the grain in rice Indian) Flint Sweet throughout the grain is responsible for consider- Pericarp, testa, able differences in vitamin content between the hyaline layer 34 5 23 8o.5 63 59 whole grains and the milled or processed products. .Aleurone layer - Endosperm 8 12.3 20 26 Vitamin E is essential for maintaining the Embryonic axis 11 0.6 2 2 orderly structure of cell membranes; it also behaves 1.6 l3 lo as an antioxidant, particularly of polyunsaturated Scutellum 47 including the brain. Deficiency symptoms, which Distribution of Thiamin in Rice and of Niacin in Rice and with alkali (Carter and Carpenter, 1982). Percentage of total niacin of total in rice in maize of the grain. thiamin (var: * Sources of data: Heathcote et al. (1952); Hinton and fatty acids. These are &undant in nf3VOuS tissue, Shaw (1953). NUTRITION 287 TABLE 14.10 Thiamin in Embryonic Axis and Scutellum of Cereal Grains* Wt of tissue Thiamin concentration Proportion of total (gi100g grain) (Pg/g) thiamin in grain (Oh) Embryonic Scutellum Embryonic Scutellum Embryonic Scutellum Cereal axis axis axis Wheat (average) 1.2 1.54 12 177 3 59 Barley (dehusked) 1.85 1.53 15 105 8 49 Rice (brown) 1.0 1.25 69 189 11 47 Oats (groats) 1.6 2.13 14.4 66 4.5 28 Rye 1.8 1.73 6.9 114 5 82 Maize 1.15 7.25 26.1 42 8 85 * Sources of data: Hinton (1944, 1948). are rare as stores of the vitamin in the body are large, include failure of nervous functions. Other functions of vitamin E are claimed by some, but these are not well substantiated by experiment (Bingham, 1987). In the ¡®OK. cerea1s ¡®Ontribute about 30% of vitamin E requirement. Wheat contains a-, B-¡¯ y- and S-tocopherols¡¯ the tota1 tocophero1 ¡®Ontent being 2¡¯0-3*4 mg¡¯lOOg* a-y p- and y- tocotrienols are also present. The biological potency of P-, y- and 6-tocophero1s are 30%, 7.5% and The total tocopherol contents of germ, bran, and 80% extraction flour of wheat are about Refinement 30, 6 and 1.6 mg/100g, respectively (Moran, 1959). a-Tocopherol predominates in germ, y- This incudes processes such as milling, that tocopherol in bran and flour, giving ct equi- separate anatomical parts of the grain to produce valents of 65%, 20% and 35% for the total a palatable foodstuff. The most palatable (lowest tocopherols of germ, bran and 80% extraction fibre), and most stable (lowest fat) parts of the flour, respectively. grains are not necessarily the most nutritious, and Quoted figures for the total tocopherol content if only these are consumed, much of the potential of other cereal grains are (in mg/100g): barley benefit can be lost. For example, 80% of the 0.75-0.9, oats 0.6-1.3, rye 1.8, rice 0.2-0.6, maize vitamin B1 is removed when rice is milled and 4.4-5.1 (mostly as y-tocopherol), millet 1.75 polished. This results from the fact that many of (mostly as y-tocopherol) (Science Editor, 1970; the nutrients reside in the embryo and outer parts Slover, 1971). of the grains (mainly in the aleurone tissue). The The oil of cereal grains is rich in tocopherols: degree of change depends upon the degree of quoted values (in mg/g) are: wheat germ oil 2.6, separation that occurs. The effects of varying barley oil 2.4, oat oil 0.6, rye oil 2.5, maize oil extraction rate in wheat milling are illustrated 0.8-0.9 (Green et al., 1955; Slover, 1971). Wheat diagramatically in Fig. 14.4, and the effects of tocopherols have particularly high vitamin E varying extraction rate on wheat and rye milling activity (Morrison, 1978). products are shown in Table 14.11. Effects of processing Some animals, including poultry, may be fed grains of various types in a totally unmodified form. Other stock may cOnSume grains that have received only minimal modification such as crushing, and some elements of the human diet, such as muesli may also contain these. Neverthe- less most cereals are consumed only after proces- sing and this affects the nutritive value of the products. Changes in nutritional properties of cereals result from several types of processing, 40% respective1y> Of that Of the alpha-tocopherol* such as: refinement, cooking and supplementation. 288 TECHNOLOGY OF CEREALS 133. - i c * 120- Carbohydrate - - constituents - v 0 "1"I IIIIII IIIII! 103 90 80 70 €0 XJ 40 100 93 80 70 60 50 40 100 90 80 70 60 50 40 Extraction rate, % Extraction rate, % Extraction rate, % FIG. 14.4 Nutrient composition of flours of various extraction rates in relation to that of whole wheat. From Kent (1983). TABLE 14.11 Cornpositton of Flour and Mtlling by-products at Vanous Extractzon Rates Material Yield Protein Oil Ash Crude Thiamin Niacin (%) (Yo) (Oh) ("1 fibre (pgk)* (Pgk)* (%I Wheatt Flour 85 12.5 1.5 0.92 0.33 3.42 85% extraction 80.5 12 1.4 0.72 0.20 2.67 19 80% extraction 70 11.4 1.2 0.44 0.10 0.7 10 70% extraction 85% extraction 10 12.6 4.7 5.1 10.6 6.0 80% extraction 12.5 14.3 4.7 4.7 8.4 10.4 191 75% extraction 20 15.4 4.7 3.5 5.2 14.0 113 85% extraction 5 11.1 3.7 6.1 13.5 4.6 80% extraction 7 12.4 3.9 5.9 11.1 5.0 302 70% extraction 10 13 3.5 5.1 8.9 6.0 232 Fine wheatfeed Bran Rye* Flour 60% extraction 60 5.7 1.0 0.5 0.2 75% extraction 75 6.9 1.3 0.7 0.5 85% extraction 85 7.5 1.6 1.0 0.8 100% extraction 100 8.2 2.0 1.7 1.6 fine 14.0 3.2 4.2 5.0 coarse 16.6 5.2 3.8 9.4 Brans§ Germs 35.5 10.3 4.8 3.4 * Naturally occuring. Sources: t Jones (1958); $ Neumann et al. (1913); 5 McCance et al. (1945). N UTRlTlON 289 TABLE 14.12 Composition of Milling Products of Various Cereals (Percent, dry basis) Cereal and fraction Protein Fat Ash Crude Carbohydrate fibre Barley Pearl barley' 9.5 1.1 1.3 0.9 85.9 Barley flour' 11.3 1.9 1.3 0.8 85.4 Barley bran3 16.6 4.4 5.6 9.6 64.3 Barley husk' 1.6 0.3 6.2 37.9 53.9 Barley dust3 13.6 2.5 3.7 5.3 74.9 Oats' Oatmeal 12.9 7.5 2.1 1.2 75.0 Rolled oats 13.3 7.6 2.0 0.9 74.7 Oat flour 14.2 7.9 2.0 1.1 73.4 Oat husk 1.4 0.4 4.5 37.8 0.9 Oat dust 10.6 5.0 6.3 22.8 10.6 Meal seeds 8.6 3.8 3.1 18.7 28.8 Oat feed meal 3.5 1.5 3.8 30.6 5.8 Brown rice4 8.5 2.21 1.4 1.0 86.9 White rice4 7.6 0.4 0.6 0.3 91.0 Parboiled rice4 8.2 0.3 0.8 0.2 90.1 Hulls5 1.1 0.4 27.3 34.1 34.1 Bran6 14.4 21.1 8.9 10.0 45.6 Bran, extracted6 17.8 0.6 11.1 12.2 57.8 Polishings' 12.1 9.9 5.5 2.2 70.3 Maize grain' 11.2 4.8 1.7 1.9 80.4 Dry milling products Rice Maize - - - Grits' 10.5 0.9 Meal' 10.1 5.7 1.2 1.4 83.7 Flour' 8.1 1.5 0.7 1 .o 88.7 Germ meal" 14.6 14.0 4.0 4.6 62.8 Hominy feed' 10.6 0.8 0.3 0.4 87.9 Corn flour" 0.8 0.07 0.1 - 99.0 High protein corn gluten meal" 68.8 6.2 2.0 1.3 21.7 Corn gluten feed" 24.8 4.2 8.0 8.9 54.1 Corn germ meal" 25.1 5.1 4.1 10.6 55.1 Wet milling products Sorghum Dry milling productsI3 Whole sorghum 9.6 3.4 1.5 2.2 Flour, crude 9.5 2.5 1.0 1.2 Flour, refined 9.5 1.0 0.8 1.0 Pearled sorghum 9.5 3.0 1.2 1.3 Brewers' grits 9.5 0.7 0.4 0.8 Bran 8.9 5.5 2.4 8.6 Germ 15.1 20.0 8.2 2.6 Hominy feed 11.2 6.5 2.7 3.8 Germ 11.8 38.8 18.6 Fibre 17.6 2.4 30.6 Tailings 39.2 - 25.3 Gluten 46.7 5.1 42.8 Squeegee 14.0 0.6 81.6 Starch 0.4 - 67.3 Solubles 43.7 - - Wet milling productsI4 290 TECHNOLOGY OF CEREALS TABLE 14.12 Continued Cereal and fraction Protein Fat Ash Crude Carbohydrate Millet14 fibre Wet milling products Starch. Germ 10.4 45.6 10.4 Fibre 11.8 6.0 13.5 Tailings 34.1 1.9 34.2 Gluten 37.8 9.0 44.0 Starch 0.7 0.1 57.5 Solubles 46.1 - - Squeegee 17.7 0.8 75.5 Sources: 'Chatfield and Adams (1940); 'Original 3rd edn; 3Watson (1953); 4U.S.D.A. (1963); 'Houston (1972); 6Australian Technical Millers (1980); 'Fraps (1916); 'Woods (1907); 'Stiver Jr (1955); "Woodman (1957); "Boundy (1957); 12Reiners et al. (1973); 13Hahn (1969); I4Freeman and Bocan (1973). TABLE 14.13 Average Nutrients in lOOg (v6 pint) of Beer Nutrient Draft Draft Keg Bottled Bottled Bottled bitter mild bitter lager pale ale stout Energy, kJ 132 104 129 120 133 156 Protein, g. 0.3 0.2 0.3 0.2 0.3 0.3 Alcohol, g 3.1 2.6 3.0 3.2 3.3 2.9 Sugars, g 2.3 1.6 2.3 1.5 2.0 4.2 Sodium, mg 12 11 8 4 10 23 Calcium, mg 11 10 8 4 9 8 Magnesium, mg 9 8 7 6 10 8 Iron, mg 0.01 0.02 0.01 0 0.02 0.05 Copper, mg 0.08 0.05 0.01 0 0.04 0.08 Riboflavin, mg 0.04 0.03 0.03 0.02 0.02 0.04 Niacin, mg 0.60 0.40 0.45 0.54 0.52 0.43 Potassium, mg 38 33 35 34 49 45 - - - Zinc, mg - - 0.02 Pyridoxin, mg 0.02 0.02 0.02 0.02 0.01 0.01 Vitamin B12 pg 0.17 0.15 0.15 0.14 0.14 0.11 Pantothenic acid, mg 0.1 0.1 0.1 0.1 0.1 0.1 Folic acid, pg 8.8 4.5 4.6 4.3 4.1 4.4 Biotin pg 0.5 0.5 0.5 0.5 0.5 0.5 Zero or trace amounts in all beers, of fat, starch, dietary fibre, vitamins A,C,D and thiamin. Source: Bingham (1987). Compositions of fractions obtained by milling other cereals are shown in Table 14.12. In the filtrations and distillations involved in Changes resulting from cooking are complex production of beers and spirits, respectively, as in only a few cases, such as boiled rice and many of the nutrients in the original grains are pasta, are cereal products cooked substantially on removed from the main product. Some nutrients their own. More frequently they are included in are derived from other ingredients, notably a recipe, so that differences between the raw vitamin B12 from yeast. cereal ingredient and the final product reflect not only changes due to cooking but also to dilution in Table 14.13. and interaction with other ingredients. Cooking The nutrients in several types of beer are shown NUTRITION 291 Maillard reactions are reactions between sugars and amino groups which give rise to browning - important in the production of commercial caramel and in providing a colour to the crust of bread and other baked products. The amino acids which engage in Maillard reactions most readily are those with a free amino group in their side-chain, particularly lysine, followed by arginine, trypto- phan and histidine. While the effects on product palatability are generally valued, there is a nutri- tional price to pay as the cross-linked sugar prevents access by proteolytic enzymes, obstructing diges- tion of the essential amino acids involved. For- tunately, the proportion of amino acids involved in crust browning is relatively small (Coultate, 1989). Probably the most significant enzymic changes that occur during processing are those involved in conversion of starch into sugars and the subsequent fermentation mediated by micro-organisms, con- verting sugars to alcohol or lactic acid. Another important example is the reduction in phytin content during fermentation and proving of bread doughs, and the accompanying increase in the more readily absorbed inorganic phosphate, due largely to catalysis by phytases produced by yeasts. Supplementation In the traditional method of tortilla production, cooking and refinement are combined as the heating of whole maize grains in alkaline water loosens the pericarp and embryo, allowing the endosperm to be concentrated. Many nutrients, including vitamins and fibre, are lost from the principal product as a result. In spite of this, niacin availability in tortillas is higher than in uncooked maize. Protein availability is generally reduced due to a number of cross-linking reactions (Rooney and Serna-Saldivar, 1987). Fortification may more than compensate for the deficiencies. In the case of parboiling of rice the nutritional properties of the refined product are improved as nutrients such as vitamins and minerals, in the parts of the grain that are subsequently removed by milling, migrate with water into the endo- sperm (see Table 10.3). The loss of vitamins on washing of milled rice is reduced but so is protein availability (Bhattacharya, 1985). Cooking losses vary according to the amount of water used, they are greater when excess water is present and least when the double boiler is used (Table 14.14). TABLE 14.14 B Vitamin lossesfiom Milled Rice Cooked by Different Methods* Nutrient Excess Absorbable Double This differs from the other types of processing water water boiler in that change in nutritional properties is its Thiamin 47 19 4 primary purpose, rather than a consequence of Riboflavin 43 14 7 an improvement in palatability. In general it Niacin 45 22 3 changes the eating qualities as little as possible. * Source: Juliano, 1985a. Because of the staple nature of cereal products, their contributions to the diets of the populations As recipes involving cereal products abound, of most of the world¡¯s nations are frequently a comprehensive illustration of changes during perceived by Governments as an important means cooking is not possible here. A selection of of ensuring adequate nutritive standards, not only examples of raw and cooked products is given in through their natural composition, but also through Table 14.15 the addition of nutrients from other sources. A more comprehensive analysis of the more Various terms are applied to such additions, common breads in the U.K. is given in Table including restoration, fortification and enrichment. 14.16. Restoration implies the replacement of nutrients lost during processing, such as milling, to the level found in the original grain, while fortifica- tion and enrichment suggest addition of nutrients Specific interactions Some of the more important interactions among not originally present, or enhancement of originally ingredients during cooking are described below. present nutrients. % loss on cooking 292 TECHNOLOGY OF CEREALS TABLE 14.15 Composition of Cereal Grains and some Products Product Energy Water Protein Fat Carbohydrate value (%) (Oh/.) (Yo) (Oh) (kJ per 10%) Wheat (and wholemeal) 14 12.7 2.2 63.9 1318 white breadmaking 14 11.5 1.4 75.3 145 1 plain 14 9.4 1.3 77.7 1450 brown 14 12.6 1.8 68.5 1377 Bran 8.3 14.1 5.5 26.8 872 Germ 11.7 26.7 9.2 (44.7) 1276 Bread white sliced 40.4 7.6 1.3 46.8 926 toasted 27.3 9.3 1.6 57.1 1129 brown 39.5 8.5 2.0 44.3 927 toasted 24.4 10.4 2.1 56.5 1158 French stick 29.2 9.6 2.7 55.4 1149 Hamburger buns crusty 26.4 10.9 2.3 57.6 1192 soft 32.7 9.2 4.2 51.6 1137 croissants 31.1 8.3 20.3 38.3 1505 Cream crackers 4.3 9.5 16.3 68.3 1857 Semi-sweet biscuits 2.5 6.7 16.6 74.8 1925 Cake (cake-mix) 31.5 5.3 3.3 52.4 195 1 Spongecake 15.2 6.4 26.3 52.4 1920 Madeira cake 20.2 5.4 16.9 58.4 1652 Pastry (short) 20.0 5.7 27.9 46.8 1874 Durum Wheat Macaroni Flour raw 9.7 12.0 1.8 75.8 1483 boiled 78.1 3.0 0.5 18.5 365 raw 9.8 12.0 1.8 74.1 1465 boiled 73.8 3.6 0.7 22.2 442 Spaghetti, wholemeal, raw 10.5 13.4 2.5 66.2 1379 boiled 69.1 4.7 0.9 23.2 485 grain and wholemeal 15 8.2 2.0 75.9 1428 rye bread 37.4 8.3 1.7 45.8 923 crispbread 6.4 9.4 2.1 70.6 1367 brown, raw 13.9 6.7 2.8 81.3 1518 boiled 66.0 2.6 1.1 32.1 597 white, easy cook raw 11.4 7.3 3.6 85.8 1630 boiled 68.0 2.6 1.3 30.9 587 oatmeal 8.2 11.2 9.2 66.0 1567 porridge (made with water) 87.4 1.5 1.1 9.0 1381 Data from Holland et 01. (1991). Reproduced with permission of the Royal Society of Chemistry. Supplementation policies usually arise in res- ponse to disasters which bring about shortages of essential foods through conflict or poverty. Thus, World War I1 was responsible for the formulation of policy in the U.K., and the Great Depression of the 1930s precipitated the institution of the U.S. fortification programme. Supplementation policy Spaghetti Rye Rice Oat may also apply specifically to cereal products expor- ted as part of an Aid Programme to populations in which a particular deficiency prevails. In the case of the U.S. the Food and Drugs Administration (FDA) has defined in the US. Code of Federal Regulations the purposes for which addition of nutrients is appropriate, as: NUTRITION 293 TABLE 14.16 Nutrient Composition of Bread in the UK (per 100g) average sliced bread Nutrient White White Brown Germ Wholemeal Water, g 37.3 40.4 39.5 40.3 38.3 Protein, g 8.4 7.6 8.5 9.5 9.2 Fat, g 1.9 1.3 2.0 2.0 2.5 Fatty acids Saturated, g 0.4 0.3 0.4 0.3 0.5 Monounsaturated, g 0.4 0.2 0.3 0.3 0.5 Polyunsaturated, g 0.5 0.4 0.6 0.7 0.7 Carbohydrate, g 49.3 46.8 44.3 41.5 41.6 Starch, g 46.7 43.8 41.3 39.7 39.8 Dietary fibre, g Southgate 3.8 3.7 5.9 5.1 7.4 3.3 (5.8) Englyst 1.5 1.5 (3.5) Energy, kJ 1002 926 92 7 Thiamin, mg 0.21 0.2 0.27 0.8 0.34 Riboflavin, mg 0.06 0.05 0.09 0.09 0.09 Nicotinic acid, mg 1.7 1.5 2.5 4.2 4.1 Sugars, g 2.6 3.0 3.0 1.8 1.8 899 914 Potential Nicotinic acid, mg 1.7 1.6 1.7 1.9 1.8 Pyridoxin, mg 0.07 0.07 0.13 0.11 0.12 Folic acid, pg 29 17 40 39 39 Pantotheruc acid, mg 0.3 (0.3) Biotin, pg 1 (1) Calcium, mg 110 100 100 120 54 Phosphorus, mg 91 79 150 190 200 0.6 6 0.2 Vitamin E, mg Tr Tr Sodium, mg 520 530 540 600 550 Potassium, mg 110 99 170 200 230 Magnesium, mg 24 20 53 56 76 Iron, mg 1.6 1.4 2.2 3.7 2.7 Tr: trace. ( ): estimated. N: The nutrient is present in significant quantities but there is no reliable information available. 0 correction of a recognized dietary deficiency; 0 restoration of nutrients lost during processing; e balancing the nutrient content in proportion to 0 avoidance of nutritional inferiority of new 0 compliance with other programmes and For any supplementation initiative to succeed it is necessary that the added nutrient is physiologic- ally available; it does not create an inbalance of essential nutrients; it does not adversely affect the acceptability of the product; and there is reasonable assurance that intake will not become excessive. Levels of addition In the U.K. the composition of flour is con- trolled by the Bread and Flour Regulations 1984 0.3 (0.3) 3 (2) Tr N Data from Holland et al. (1991). (SI 1984, No. 1304), as amended by the Potassium Bromate (Prohibition as a Flour Improver) Regu- lations 1990 (SI 1990, No. 339). Flour derived from wheat and no other cereal, whether or not mixed with other flour, must contain the follow- ing nutrients in the amounts specified: the caloric content; products replacing traditional foods; regulations. Nutrient Required quantity (in mgllOOg) Calcium not less than 235 and not more than 390 not less than 1.65 Iron Thiamin not less than 0.24 Nicotinic acid" or not less than 1.60 Nicotinamide* carbonate * also known as niacin. The requirement concerning calcium carbonate does not apply to wholemeal, self-raising flour (as they have a calcium content of not less than 0.2%) or wheat malt flour; while iron, thiamin and 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. Vitamins 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). Distribution of vitamins in cerea,s Variation in content from one cereal to another is remarkably small except for niacin (nico- tinic acid), the concentration of which is rela- tively 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 B1 Thiamin Embryo (scutellum) The distribution of these vitamins in the wheat B2 Riboflavin Most parts grain is also shown diagrammatically in Fig. 14.3. B6 Pyridoxin Aleurone B12 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 scutel- lum, 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 over one tenth of the total in the grain, a larger E Tocopherol and tocotrienol Embryo K Phylloquinone proportion than that found in the other cereals (see Table 14.10). 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 com- plex of polysaccharide and polypeptide moieties TABLE 14.6 Vitamins and their Occurrence in Cereals Vitamins are sometimes classified according to Cereals, except maize, contain @p@f'k% which 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) NUTRITION 295 An estimate of daily phytate intake in the U.K. is 600-800 mg. Of this 70% comes from cereals, 20% from fleshy fruits and the remainder from vegetables and nuts (Davies, 1981). The reduced bioavailability of minerals due to phytate depends on several factors, including the nutritional status of the consumer, concentration of minerals and phytate in the foodstuff, ability of endogenous carriers in the intestinal mucosa to absorb essential minerals bound to phytate and other dietary substances, digestion or hydrolysis of phytate by phytase andor phosphatase in the intestine, processing operations, and digestibility of the foodstuff. The ¡®other substances¡¯ referred to include dietary fibre (non-starch polysaccharides) and polyphenolic compounds. Many metal ions form complexes with phytate, including nickel, cobalt, manganese, iron and calcium; the most stable complexes are with zinc and copper. The phosphorus of the phytate molecule itself is also only partly available to non- ruminant animals and humans; estimates vary from 50 to 80% and depend upon several factors includ- ing the calcium-phytic acid ratio (Morris, 1986). The presence of phytate may also influence the the nature of the phytate-protein complexing being dependent on pH. The mechanisms involved are complex and ill-understood but it is greatest at Cereal Fraction Maize Endosperm 0.04 3 (4) low pH because, under these conditions, phytic Embryo 6.39 87 (95) acid has a strong negative charge and many plant proteins are positively charged. Very little com- Hull 0.07 plexing between wheat proteins and phytate has Wheat Endosperm 0.004 2 (1) Embryo 3.91 12 (29) Aleurone 4.12 86 (70) been found and complexing between rice bran Embyro 3.48 ¡°Pericarp¡± 3.37 80.0 (71) below pH 2.0 (Reddy et al., 1989). (31) Embryo 2.66 Bran 0.99 (1 1) these allows monitoring to be carried out, provid- ing a means of ensuring their safe and proper use. Ph ytic acid An important constituent of cereals, legumes and oilseed crops is phytic acid. The systematic name of phytic acid in plant seeds is myoinositol-1,2,3,5/ 4,Chexakis (dihydrogen phosphate) (IUPAC-IUB, 1968). Phytic acid in the free form is unstable, decomposing to yield orthophosphoric acid, but the dry salt form is stable. The terms phytic acid, phytate, and phytin refer respectively to the free acid, the salt, and the calcium/magnesium salt, but some confusion arises in the literature where the terms tend to be used interchangeably. The salt form, phytate, accounts for 85% of the total phosphorus stored in many cereals and legumes. In cereals its distribution varies, in that in maize the majority lies in the embryo, while in wheat, rye, triticale and rice most of the phytate is found in the aleurone tissue. In pearl millet the distribution is apparently more uniform (Table 14.18) TABLE 14.18 Cereals Distribution of Phytate in the Morphological Components of functional and nutritional properties of proteins, YO of total Phytate % in grain < O.¡¯ (l) Rice Endosperm 0.01 7.6 1 (3) (26) phytate and rice bran proteins occurred only Pearl millet Endosperm 0.32 (48) Inhibition of the activity of enzymes such as trypsin, pepsin and aZpha-amylase by phytic acid has been reported. In the case of the amylase phytic acid complexing with the enzyme itself, or chelation of the Ca2+ ions required by the enzyme. Tannins Tannins are phenolic compounds of the flavo- noid group, that is they are derivatives of flavone. They are considered in the ¡®negative¡¯ attributes Values from Reddy et al. (1989). The values in parenthesis are calculated from the table values, using the proportions given by Kent (1983). enzyme it is not clear whether this results from the The negative nutritional attributes of phytate derive from the fact that it forms insoluble complexes with minerals, possibly reducing their bioavailability and leading to failure of their absorption in the gut of animals and humans, and thus to mineral deficiencies. 296 TECHNOLOGY OF CEREALS TABLE 14.19 Percentage of Tannin in Cereal grains at 14% Moisture Content Brown Rice Wheat Maize Rye Millet Barley Oat Sorghum 0.1 0.4 0.4 0.6 0.6 0.7 1.1 1.6-(5)* Data from Juliano (1985a). * Collins (1986). section of this chapter because it is alleged that hangover. It also has an inhibiting effect on the they reduce protein digestibility through phenol- nervous system, including the brain, inducing protein complexing. Some flavonoids have also euphoria and depressing judgement. The amount been implicated as carcinogens. On the other of alcohol required to induce intoxication depends hand, they have also been credited with the ability on the individual, influential factors being body to stimulate liver enzymes which offset the effects weight, sex and drinking habits, regular heavy of other carcinogens. Clearly we know little about consumers developing a higher threshold than the nutritional effects of tannins (Bingham, 1987). infrequent drinkers. It is generally considered There is no doubt that they and their derivatives that symptoms of intoxication are apparent when can adversely affect flavour and colour, thus blood contains 100 mg/100ml alcohol (a 70 kg reducing palatability. man drinking 1.6 1 (3 pints) of beer, containing Although present in all cereals, tannins are 50 g ethanol, achieves this level). Reactions are particularly associated with sorghums of the impaired below this level however, and in the ¡®birdproof¡¯ type. All sorghums contain phenolic U.K. the limit for someone in charge of a motor acids and other flavonoids, but only brown types vehicle is 80 mg/lOOml, in some countries it is contain procyanidin derivatives, otherwise known zero. The intoxicant effect on women is usually as condensed tannins. Table 14.19 shows their greater than on men as their bodies metabolize relative abundance in cereal species. the alcohol more slowly and their body weight is generally lower than that of men. Moderate drinking is regarded as less than 50g of alcohol per day for men, and 30g for women. Harmful effects of alcoholic drinks Most beers contain 24% w/w. of alcohol, Long term effects of alcohol consumption are barley wine contains 6%. Lagers contain less damage to the heart, liver (cirrhosis is a condi- alcohol than ales and stouts but it is absorbed tion in which some liver cells die) and brain. more rapidly from lagers because of their greater Cancers of the mouth, the throat and the upper effervescence. Spirits whether produced from digestive system particularly, are statistically grains, other fruits or starch, contain about 33%. associated with regular heavy consumption of Low to moderate consumption of alcohol in- alcohol. creases life expectancy, reduces blood cholesterol Allergies concentration and (in France) is associated with low incidence of coronary vascular disease. How- ever, alcohol is a drug which can become addic- An allergy is an unusual immune response to tive, it is rapidly absorbed into the blood, one a natural or man-made substance that is harmless fifth of the amount being ingested, through the to most individuals. Hypersensitivity is a non- stomach wall and the remainder from the small immune response to a substance which generates intestine. Following ingestion of alcohol, blood responses whose symptoms can be similar to vessels become dilated and body heat loss is allergies. Allergies involve abnormally high re- accelerated, overriding the body¡¯s thermoregula- actions of the body¡¯s natural immune mechanisms tory mechanisms - sometimes dangerously. against invasion by foreign substances. Substances From the blood, alcohol diffuses widely; it is a that stimulate an immune response are known as diuretic, promoting the production of urine, giving antigens, and when the response is abnormal the rise to dehydration - one of the causes of the antigens involved are called allergens. The subject N UTRlTl ON 297 of cereals as allergens was reviewed by Baldo and cannot easily be established as similar symptoms Wrigley (1984). have been detected in the absence of allergies. Allergies arise to substances that enter the Coeliac disease is a pathologial condition, lead- body as a result of inhalation or ingestion, alter- ing to loss of villi and degeneration of the intestine natively they can be a response to skin contact. wall, and induced by gliadin and gliadin-like Cereal pollens and fragments between 1 and 5 proteins. Other names by which it is known are pm present in the dust raised when grains or gluten sensitive enteropathy, sprue, nontropical sprue other plant parts are being handled, constitute and idiopathic steatorrhea. Symptoms of the disease the inhaled antigens. While everyone is likely are malabsorption and the resulting deficiencies of to inhale some pollen grains, of cereals and vitamins and minerals, and a loss of weight. many other species, those people involved in Its cause remains unknown, although there is handling cereals are more likely to inhale grain some evidence that it results from a genetic defect dust. characterized by the absence of an enzyme neces- One of the best documented and longest estab- sary for gliadin digestion. Alternatively it may lished allergies associated with cereals is bakers¡¯ involve an allergic response in the digestive asthma. As the name implies, bakers¡¯ asthma and system. Most coeliac patients are childen, the rhinitis are most prevalent in, but not exclusive symptoms showing when cereals are first intro- to, those who habitually handle flour. It is now duced in their diet. In a normal condition cells established as a IgE mediated reaction (i.e. it is lining the small bowel absorb nutrients which are a true allergy - IgE is an immunoglobulin duly passed into the blood, but, in coeliac patients, associated with an allergic response) arising from the cells are irritated and become damaged. Their inhalation of airborne flour and grain dust. As an resulting failure to absorb leads to vomiting, occupational disease it is declining as a result passing of abnormal stools containing the un- of improved flour handling methods creating absorbed nutrients, and to symptoms such as pot progressively less dust. Nevertheless significant belly, anorexia, anaemia, rickets and abnormal proportions of bakery and mill workforces exhibit growth. Milder forms may pass unnoticed, but in some sign, though not necessarily asthmatic adult life, may result in general itl health, weight symptoms, of the allergy. loss, tiredness and osteomalacia. Newly diagnosed Many studies have been made on the harmful adults probably were born with the disease, but effects of inhaling grain dusts, for example, their symptoms presented only in later life. comparisons of grain handlers with city dwellers Treatment consists of strict adherance to a in an American study showed that inhalation of gluten-free diet. All untreated wheat flour must grain dust gave rise to serious problems in the be avoided, and rye, triticale, oat and barley lungs. Chronic bronchitis was significantly higher products are also excluded. Maize and rice (and in grain handlers (48%) than in controls (17%), probably millet and sorghum) are accepted as as was wheezing at work (¡®occupational asthma¡¯), being totally gluten-free. Because cereal flours are and airway obstruction. Compared with smoking, so versatile, gluten is unexpectedly present in grain dust exposure had a greater effect on the many foods and labelling requirements are in- prevalence of symptoms but had the same or less adequate to indicate its presence in all cases. effect on lung function (Rankin et al., 1979). In Manufacturers and consumers of gluten-free pro- other studies skin-prick tests, which are a means ducts can confirm the absence of gluten using of detecting allergic responses, confirmed their antibody test kits. Some successful kits use anti- occurrence following exposure to grain dust (Baldo bodies raised to wheat o-gliadins. Although these and Wrigley, 1984). are not considered to be toxic (it is the a- and p- While it is clear that inhalation of dusts is gliadins that are) they retain their antigenicity harmful, and that immune responses are demon- after heating and are thus suitable for use on strable, the degree of responsibility for the cooked products as well as raw ingredients (Skerrit symptoms attributable specifically to allergy et al., 1990). 298 TECHNOLOGY OF CEREALS Schizophrenia Evidence of the implication of cereal prolamins as a contributory factor to the incidence of schizophrenia in genetically susceptible patients has been reviewed by Lorenz (1990)* Much Of the evidence in favour of the association is epi- demiological , but some clinical trials support it. Coeliac disease is reported to occur considerably more frequently in schizophrenic patients than would be expected by chance alone, and admini- stration of gluten-free diets has in some cases led to remission of both disorders. Not all studies support a relationship between gluten ingestion and schizophrenia, and the difficulties involved in designing definitive experiments in this area make a rapid conclusion to the question unlikely. Dental cartes This is an infectious disease that leads to tooth decay through the production of organic acids by bacteria present in the oral cavity. The bacteria are supported by fermentable sugars and starch, and foods containing high proportions of these nutrients have been investigated in view of their perceived potential to encourage development of the disease. Lorenz (1984) reviewed work on the cariogenic and protective effects of diet patterns, with particular reference to cereals. There is a gen- era1 concensus that sugary foods, particularly sticky ones, which remain in the mouth for a long time, do lead to increases in the occurrence and severity of caries in susceptible subjects. There are reports that the disease is prevalent among The disease gangrenous ergotism, caused by the sclerotia of the fungus Claviceps purpurea - is considered to be cariogenic and no difference between white and wholemeal breads has been discussed in Ch. 1. established in this context. Cereal products with a high sucrose content, such as cakes and Mycotoxins sweet biscuits, can increase caries, but the rela- tionship is not simple and many factors are These are toxic secondary metabolites involved. Corn- based breakfast cereals have been produced by fungi. Technically, the toxins in shown to be more cariogenic than those made poisonous mushrooms and in ergot are myco- from wheat or oats but conflicting results have toxins, but poisoning by mushrooms or by ergot emerged from different trials in which sucrose- requires consumption of at least a moderate coated breakfast cereals were compared with amount of the fungus tissues containing the uncoated equivalents. Lorenz (1984) concluded toxins, whereas the mycotoxins in, for example that few unquestionable guidelines can at present be offered as to the avoidance or cariogenic foods. P-Glucans A number of negative nutritional effects have been associated with beta-glucas. They may impair absorption of mineral and fat soluble vita- mins, but additional research is required in this area. Perhaps the most extensively studied negative nutritional factor involves reduced growth rates of chickens fed barley-based diets. Barley is of low digestibility and low energy value when fed to chickens, resulting in poor growth and production. Low production values are attributed to P-glucans, as supplementation with P-glucanase improves the performance of barley-based diets (Pettersson et al. , 1990). Presumably P-glucans in the endo- sperm cell wall physically limit the accessibility to starch and protein, and increase digesta viscosity. Non-cereal hazards Adverse effects on health can arise from the consumption of foods contaminated by toxic substances. In the handling of all food raw materials, some risk of contamination exists and cereals are no more susceptible than other natural products to these. Similarly, all natural products are associated with particular risks from, for example, infection with specific diseases. Hazards of this sort are considered here. E rgotisrn bakers and bakeq workersY but bread is not consumption of products containing 'ergof - NUTRITION 299 nuts or cereal grains, may be present in the duced mainly by species of Fusarium, the major absence of any obvious mould. Strictly, substances producers being members of the F. roseum com- like penicillin and streptomycin are mycotoxins, but plex. Zearalenone is an oestrogen and its effects the term is usually reserved for substances toxic primarily involve the genital system. Most affected to higher animals (including humans). The term are pigs, the effects on humans are not well ¡®antibiotics¡¯ is generally applied to compounds documented. Although reported in wheat, barley, produced by fungi that are toxic to bacteria. oats and sorghum, maize is the cereal most affected. Nearly 100 species of fungus were associated Trichothecenes are a group of about 40 com- with mycotoxins giving rise to symptoms in pounds associated with Fusarium spp. but also domestic animals, by Brooks and White in 1966. produced by other fungi. These mycotoxins are Of these over half were in the genera Aspergillus, implicated as causes of Alimentary toxic aleukia in Penicillium, and Fusarium. man. Occurrence of the disease in Russia between Mycotoxins cause relatively little concern in 1931 and 1943 was associated with consumption cereals, compared with peanuts, Brazil nuts, pis- of proso millet that had been left in the field over tachio nuts and cottonseed, the risks depending to winter and had become seriously infected with a some extent on their place of origin. Nevertheless, number of fungal species. Trichothecenes have maize is an excellent substrate for the growth of been isolated from other cereal species, but Aspergillus flavus and A. parasiticus, two fungal mainly maize stored on the cob. species that produce aflatoxins. The importance Ochratoxin is associated with spontaneous nephro- of mycotoxins in the cereal context was reviewed pathy in pigs, this mycotoxin from Penicillium by Mirocha et al. (1980). virididicatum, has been found in stored (often overheated) maize and wheat, in North America and Europe. Aflatoxins Citreoviridin, Citrinin and other mycotoxins are There are six important aflatoxin isomers: B1, described as ¡®yellow-rice toxins¡¯ as they cause Bz, G1, GZ, MI and Mz; the initial letter of the yellowing of rice in storage. They are associated first four being that of the colour of the fluore- with diseases of the heart, liver and kidneys and scence which they exhibit under ultraviolet light, they are produced mainly by Penicillium citre- i.e. Blue, and Green. The M indicates Milk, in ovariden, P. citrinum and P. islandicum. which these isomers were first found (this is Limits on aflatoxin levels between 5 and 50 systematic?). All isomers are toxic and carcinogenic pg/kg have been set by developed countries for but aflatoxin B1 is the most abundant and presents cereals and other commodities intended for feed the greatest danger to consumers. Several deriva- or food use. The actual exposure that will produce tives, produced by the microorganisms or in the cancer in humans has not been established and consuming animal are also toxic. limits for all mycotoxins are based, not on In the United States it has been found that infec- scientific principles but notional concepts of safety. tion of maize with Aspergillus spp. occurs in the While this state of affairs persists, international field, usually after damage to the grains by insects. agreement on standards, though desirable, is Degree of infection varies geographically, growth unlikely (Stoloff et al., 1991). of the organism being favoured by high tempe- ratures. It is thus most common in the southeast References U.S.A. and tropical maize-growing countries such as Thailand and Indonesia and relatively rare in AUSTRALIAN TECHNICAL MILLERS ASSOCIATION (1980) Current use and development of rice by-products. Australas. the cooler Corn Belt of North America. Other Bake Millers J. 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