NUTRITION 279 a particularly high calorific value; in fact that of fat is higher, at 37 k(9 kcal) per gram, as is alcohol at 29 k7(7 kcal)per gram than that of 3 starch Protein content and quali Cereals including bread, contribute approxim tely 25% of the protein in the average adult diet in the u. K. Three thin slices of bread contribute much protein as an egg In nutritional terms there are two factors of a prime importance in relation to protein: the total 2 protein content, and the contribution that essen- tial amino acids make to the total There are eight essential amino acids(out of a 你N total of 20 or s methionine, tryptophan, tonnes oa aline, isoleucine, leucine, phenylalanine and lysine. Two other amino acids are sometimes classified as essential but they can be made in the Cow's miLkBeef body- tyrosine from phenylalanine and cysteine/ cystine from methionine. Their presence in foods reduces the requirements of the relevant FIG 14. 1 The essential amino acids in food proteins. The roportions of each essential amino acid are she essential amino acids. In foods derive d as the percentage of the total essential amino acids plants in general, the sulphur-containing ultate,1989, by courtesy of The Royal Society of acids methionine and cysteine are most likely to be limiting, but this is not true of cereal grains Protein n cereals, lysine is the first to be limiting: rice, oat and rye are relatively rich among wholegrain Embryo Scutellum 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/16g of N Perica and test Maize protein is also limiting in tryptophan, based on the reference value of 1.0 g/16g of N, which the other cereals just reach. A comparison between wheat protein and protein from other food sources is shown in Fig. 14.1 FIG. 14.2 Distribution of total pr The figures show the percentage of the total protei In the h was made of of animal-derived proteins, containing, as they by J.J.C, Hinton. From The Research Association of Brtish do, the correct proportions of essential amino acids. However, protein types are rarely eaten alone and they tend to complement each other; anatomical parts of the grain; and in the endo- for example bread may be eaten with cheese, a sperm, by the contributions of the different good source of lysine. Even in vegetarian diets, protein fractions(albumins, globulins, prolamins, many legumes and nuts supply essential amino glutelins) acids. a good combination is rice and peas The insoluble fractions are particularly deficient in Both content(Fig. 14.2)and composition of lysine, as illustrated in the comparison of the solu- protein are affected by the contributions of different bility fractions of wheat endosperm(Table 14. 2)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)