Maize amino acid content

Soya beans contain oil (180-220 g kg ) and approximately 35-45% protein (370-420 g kg ). The amino acid content differs significantly from that of wool and silk protein (see Table 13.1). Soya bean protein content is higher than that of peanuts (approximately 25% protein) and maize (approximately 10% protein). The principal components of this protein are... 

Animal feeds are a major market, especially for monogastric animals. This is because their nutritional requirements are high and the lysine content of traditional feed such as soy or maize is low. A supplementation of feeds with individual essential amino acids is necessary because a high protein contents lead to excessive manure production, especially by pigs. 

In nonlegumes, Mo deficiency hampers NOj" reduction and decreases the amounts of most amino acids. Addition of Mo to deficient plants has been found to increase the contents of glutamic acid, glutamine, a-alanine, serine, and aspartic acid in spinach Spinacea oleracea L.), cauliflower, tomato Lycopersicon esculentum Mill.) (Mulder et al., 1959), and maize (Berducou and Mache, 1963). However, decreases in the contents of some amino acids and amides during later stages of growth of Mo-fertilized crops can result from their incorporation into proteins or from subsequent metabolic reactions such as transamination reactions or conversion to amides (Possingham, 1957). 

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. 

Coumarin reduced labeled glucose incorporation and carbohydrate and protein content of the cytoplasm of Pythium, but enzymes related to the metabolism of cell wall polysaccharides were not affected [296]. It has been reported that moulds are more sensitive to coumarin when they are cultured on the simple synthetic nutrient medium than on the yeast water [140]. This suggests that coumarin blocks the synthesis of an unknown metabolite of ndamental importance. Coumarin was found to affect the level of a variety of free amino acids present in a cell. In addition, some nucleic acid precursors partially reverse the coumarin-induced inhibition of maize mesocotyle [131]. The stimulation of germination and growth caused by coumarin in low concentrations may be assumed as a supercompensation mechanism. 

Zeins, the major storage proteins of maize belonging to the prolamins. In maize, the ethanol-soluble or protamine fraction consists of the zeins (Mr 10-22 kDa) that constitutes as much as half of the total protein of the endosperm. They are characterized by a high content of Glu (23%) and Leu (19%). The amino acid sequence of a representative of the zeins has been derived from the nucleotide sequence of a zein cDNA clone [D. Geraghty et al.. Nucleic Acids Res. 1981, 9, 5163]. 

Prolamines a group of simple (unconjugated) proteins, soluble in 90% ethanol. They occur in cereals, and contain up to 15 % proline and 30-45 % glutamic add, but they have only low contents of essential amino acids. The chief representatives are gliadin (wheat and rye), zein (maize contains no tryptophan or lysine) and hordein (barley contains no lysine). Oats and rice do not contain P. 

The maize kernel contains two main types of protein. Zein, occurring in the endosperm, is quantitatively the more important, but this protein is deficient in the indispensable amino acids tryptophan and lysine (see Fig. 22.2). The other protein, maize glutelin, occurring in lesser amounts in the endosperm and also in the germ, is a better source of these two amino acids. Varieties of maize have been produced with amino acid components different from those present in normal maize. One such variety is Opaque-2, which has a high lysine content. The difference between this variety and normal maize is primarily attributed to the zein/glutelin ratio. 

The protein contents of various fishmeals vary over a range of about 500-750 g/kg, but the composition of the protein is relatively constant. It is rich in the essential amino acids, particularly lysine, cystine, methionine and tryptophan, and is a valuable supplement to cereal-based diets, particularly where they contain much maize. The essential amino acid composition is compared with that of ideal protein (see Table 13.7 in Chapter 13) in Box 23.3. 

Aspartic add and aspart hic The average content of aspartic add in proteins is 5.5% the average content of asparagine is 4.4%. Aspartic add is the major amino acid of animal proteins known as globuhns and albumins (6-10%). Vegetable proteins contain 3-13% aspartic add, mainly in the form of asparagine (e.g. wheat proteins contain about 4% and maize proteins about 12%). 

The reduction in dietary CP content consisted of replacing soybean protein concentrate by maize starch with supplementation of amino acids to meet the requirements. 

Since the 1940 s, c. is the classical example for practical applications of the ->hybrid breeding technique that makes use of the different gene pools of c. by combining the best fitted individuals to create more vigorous, cold-tolerant and high-yielding varieties, which made c, the no. 1 crop in the US and also the most important feed and starch crop in northern Europe. For food applications, it was necessary to raise the protein content to over 20% and to improve the amount of the essential - amino acids lysine and tryptophane. C. is used for 75% of the world s starch production. For food as well as for technical applications, - amylo-maize starch varieties (high-amylose c.) were bred. 

Maize with enhanced protein content and enriched in essential amino acids is an important object of research and development to serve as a food basis for coimtries in Afiica, South and Middle America and Asia. 

The data presented here show that shortly after etiolated leaves have been illuminated, the rate of synthesis of plastid RNA and certain plastid enzymes increases. Mego and Jagendorf (1961) found that the protein content per plastid increases markedly as etiolated bean leaves become green. Williams and Novelli (1964) found ribosomes of illuminated leaves from dark-grown maize to be more active than ribosomes from unilluminated leaves in the in capacity to incorporate amino acids into trichloroacetic acid-insoluble materials, but the increased activity could be detected only after a few hours of illumination or after 1 hour in the light followed by 1 hour of darkness. Thus,... 

---