Cereals, amino acid content

The nutritional value of proteins (see p. 360) is decisively dependent on their essential amino acid content. Vegetable proteins—e.g., those from cereals—are low in lysine and methionine, while animal proteins contain all the amino acids in balanced proportions. As mentioned earlier, however, there are also plants that provide high-value protein. These include the soy bean, one of the plants that is supplied with NH3 by symbiotic N2 fixers (A). 

Since dietary cereals are low in sulfur-containing amino acids, they produce an alkaline urine which favors the retention of bone minerals. In post-menopausal women, there appears to be some interaction between the diet and the effect produced by estrogens on bone mineral content (28). 

Pea.nuts, The proteins of peanuts are low in lysine, threonine, cystine plus methionine, and tryptophan when compared to the amino acid requirements for children but meet the requirements for adults (see Table 3). Peanut flour can be used to increase the nutritive value of cereals such as cornmeal but further improvement is noted by the addition of lysine (71). The trypsin inhibitor content of raw peanuts is about one-fifth that of raw soybeans, but this concentration is sufficient to cause hypertrophy (enlargement) of the pancreas in rats. The inhibitors of peanuts are largely inactivated by moist heat treatment (48). As for cottonseed, peanuts are prone to contamination by aflatoxin. FDA regulations limit aflatoxin levels of peanuts and meals to 100 ppb for breeding beef catde, breeding swine, or poultry 200 ppb for finishing swine 300 ppb for finishing beef catde 20 ppb for immature animals and dairy animals and 20 ppb for humans. 

Niacin was discovered as a nutrient during studies of pellagra. It is not strictly a vitamin since it can be synthesized in the body from the essential amino acid tryptophan. Two compounds, nicotinic acid and nicotinamide, have the biologic activity of niacin its metabolic function is as the nicotinamide ring of the coenzymes NAD and NADP in oxidation-reduction reactions (Figure 45-11). About 60 mg of tryptophan is equivalent to 1 mg of dietary niacin. The niacin content of foods is expressed as mg niacin equivalents = mg preformed niacin + 1/60 X mg tryptophan. Because most of the niacin in cereals is biologically unavailable, this is discounted. 

The grain or pulse forms of legumes have a high total protein content (20-26%) and can therefore be used as a natural supplement to cereals. Pulses are normally deficient in the essential amino acids methionine and cystine but contain enough lysine, whereas cereals are deficient in lysine but contain enough methionine and cystine. 

Dogs and cats are carnivores that have adapted to also eating cooked cereal carbohydrates and oilseed proteins. Cats are the more obhgate carnivores, typically requiring higher protein content foods on a dry matter basis. Currently, they are the only domesticated animal for which a dietary essential level of taurine, an amino acid found mainly in meat, has been established. 

Soybean proteins are widely used as food additives in European derived societies, primarily in processed foods, and this trend continues to grow annually. This makes soybean proteins a pervasive component of the human diet in industrialized countries. Solvent extracted soybean meal is also widely used as an animal feed additive (ref. 5, for review), because it is an inexpensive source of high quality protein that contains more of essential amino acids lysine and tryptophan than most cereal crops. Combined with corn, the other primary feed grain used in the United States, a ration can be assembled that is adequate in both sulfur amino acid and lysine contents, and provides a high protein diet that is well balanced for poultry and pigs. 

Lysine is the first nutritionally limiting essential amino acid in most cereals (1.5-4%) tryptophan (0.8-2%) is the second limiting amino acid in maize, and threonine (2.7-3.9%) in other cereals. The high content of prolamins in cereals is responsible for the low content of essential amino acids like lysine, threonine, valine and isoleucine. Rice and oats have a better balance of essential amino acids than other cereals due to a lower content of prolamins. 

Nuts, seeds, and grains are not considered as sources of organic acids. Other than amino acids and fatty acids, they contain phenolic acids and phytic acid. Phytic acid and its salts, phytats, are regarded as the primary storage form of both phosphate and inositol in seeds, mostly within the hulls. The phytic acid content of cereals (whole grain) varies from 0.5% to 2.0% [21],... 

Dietary copper intake is approximately 1-2 mg/day. Quoted copper contents of foods are unreliable. While some foods, such as meats and shellfish, have consistently high concentrations, others such as dairy produce are consistently low in copper. However, the copper content of cereals and fruits varies greatly with soil copper content and the method of food preparation. Estimates of copper intake should include water copper content, and the permitted upper copper concentration for drinking water is 2mg L. Approximately 10% of dietary copper is absorbed in the upper intestine, transported in the blood loosely bound to albnmin, certain amino acids and peptides. Finally, most of the ingested copper is taken np by the liver. Copper homeostasis is critically dependent on the liver becanse this organ provides the only physiologically relevant mechanism for excretion of this metal. 

Less research has been carried out on millets than on other cereals. Nutritional quality is one area of priority. Like other cereals, millet has low contents of essential amino acids. For example, pearl millet contains in the order of 3 g lysine/100 g protein, whereas the World Health Organization recommends a minimum of 5.5 g/100 g. On the plus side, millets do not contain gluten proteins, so they are safe for those with celiac disease. Millets are low in certain minerals, including calcium. 

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