Amino acids in cereals

Characteristically, legume seeds are rich in protein and contain intermediate to high levels of lysine and threonine which are important in balancing the deficiencies of these essential amino acids in cereal diets. Certain legume proteins, such as soybean, also exhibit strong functional properties, especially water solubility, water and fat binding and emulsification. Thus soybean flours, protein concentrates and isolates have been used widely as nutritional supplements and functional ingredients in foods. 

JM Concon. Chemical determination of critical amino acids in cereal grains and other foodstuffs. In M Friedman, ed. Protein Nutritional Quality of Foods and Feeds. Part 1 Assay Methods—Biological, Biochemical, and Chemical. New York Marcel Dekker, 1975, pp 311-379. 

Fater et al. (1983) used overpressurized TLC (OPTLC) to determine amino acids in cereals very tight zones were formed in 75 min, and 10-20 samples were separated on a single plate. Ahraham et al. (1983) also used OPTLC for the separation of reduced and oxidized forms of glutathione from amino acid mixtures. 

Fater, Z., Kemeny, G., Mincsovics, E., and Tyihak, E. (1983). Determination of amino acids in cereals by overpressured thin-layer chromatography. Dev. Food Sci. 5A 483-488. 

From the nutritional point of view, denaturation is usually desirable since denatured proteins are more amenable to digestive enzymes than the native proteins. Denaturation, therefore, increases the bioavailabihty of proteins (e.g. sulfur-containing amino acids in cereals and legumes). Some antinutritional and natural toxic substances are also denatured, such as protease inhibitors (see Section 10.2.1.1), lectins (see Section 10.2.2.6), enzymes and other unwanted proteins and undesirable microorganisms. 

Chung, O.K., and Pomeranz, Y. 1985. Amino acids in cereal proteins and protein fractions. Chapter 5 in Digestibility and Amino Add Ayailability in Cereals and Oilseeds. J.W. Finley and D.T. Hopkins (eds.). American Association of Cereal Chemists. St. Paul, MN. 

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). 

Nutritive value of foods and feedstuffs depends to a large degree on protein level and quality, i.e., the relative amounts of the component amino acids compared to the requirements of the animal for various metabolic functions. The cereal grains are notoriously low in certain essential amino acids. Usually lysine is the first or second limiting amino acid. The grain of rye (Secale cereale L.) exhibits an amino acid profile superior to that of other cereal grains, especially wheat (1,2,3,4,5). Despite this fact, lysine is still the first limiting amino acid in rye in most instances (6,7). 

ALS herbicides. Two classes of ALS-inhibiting herbicides are the sulfonylurea herbicides, discussed in Sections 2.1.2.1 and 2.2.3.1, and the imidazolinone herbicides. A third class of ALS-inhibiting herbicides is the 1,2,4-triazolo [1,5-a]pyrimidine-2-sulfonanilides. The triazolopyrimidine sulfonanilides act by disrupting the biosynthesis of branched chain amino acids in plants. Representatives of this class of herbicides include florasulam (Boxer , Nikos ) [151], initially introduced in Belgium in 1999 and used for the postemergence control of broadleaf weeds in cereals and corn, and flumetsulam (Broadstrike ) [152], used alone or in combination with other herbicides for the control of broadleaf weeds in soybean and corn. 

Thiele, C., Ganzle, M.G., Vogel, R.F. 2002. Contribution of sourdough lactobacilli, yeasts, and cereal enzymes to the generation of amino acids in dough relevant for bread flavor. Cereal Chem 79 45-51. 

As yet methionine, the other amino acid in which cereals are deficient, is only produced from pentaerythritol or acrolein by synthetic means, not by fermentation [71], which yields the DL product (e.g., Eq. 16.29). 

The biological value of food proteins is greatly influenced by the ratio of their essential amino acids. Most food proteins, first of all plant proteins, are deficient in some essential amino acids. The limiting essential amino acid in legume and milk proteins is methionine, and in cereal proteins it is lysine. Beside the knowledge of the requirements of quality and composition of amino acids, it is equally important to know whether these amino acids can be best utilized as free amino acids, in the form of peptides or proteins. The following possibilities exist for improving the balance of essential amino acids in the proteins ... 

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. 

Threonine was discovered by Rose in 1935. It is an essential amino acid, present at 4.5-5% in meat, milk and eggs and 2.7-4.7% in cereals. Threonine is often the limiting amino acid in proteins of lower biological quality. The bouillon flavor of protein hydrolysates originates partly from a lactone derived from threonine (cf. 5.3.1.3). 

Glutamic acid is the most abundant amino acid in the nervous tissue. In conventional proteins, both amino acids are usually found in larger quantities (especially in globulins) in cereal and legume proteins (18-40%). Wheat gluten (in its component gliadin) contains about 40%, soy protein contains about 18% and milk proteins contain about 22% of glutamic acid. 

Lysine is an essential amino acid. The body requires lysine but cannot synthesize it so it must be provided in the diet. High quality protein foods provide lysine. However, lysine is the limiting amino acid in most cereals— foods for much... 

Pea protein is moderately deficient in the amino acids methionine and cystine, which are supplied in ample amounts by cereal proteins. However, the legume protein contains sufficient lysine to cover the deficiency of this amino acid in grain proteins. Hence, combinations of peas and cereal products supply higher quality protein than either food alone. 

Proteins are the second largest group of compounds in endosperm (12-15%). Cereal proteins are classified based on their solubility characteristics water soluble albumins (5-10%), dilute salt-solution soluble globuhns (5-10%), aqueous alcohol soluble prolamins (40-50%) and dilute acid or alkah soluble glutelins (30-40%) (Godon, 1994). Cereal proteins, similar to other plant proteins, are low in some of the essential amino acids, for example lysine. Glutamic acid is the major amino acid in wheat. 

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