Maize amino acid composition

If these results can be relied on, it suggests that the different behavior of wheat and maize proteins may depend on differences in amino acid composition/structure of the functional proteins rather than differences in their relative proportions. How these differences might influence the Tg is an area that offers a challenge for future research. Of course. 

In some circumstances it is possible to express protein requirements in terms of total protein alone, for example if animals are fed on a limited range of foods of known amino acid composition. This is the case for growing pigs in the USA that are fed mainly on maize and soya bean meal. Such a simplified approach cannot be sustained when a wider range of foods and by-products are used, and when diets must be formulated not only to maximise growth but also to optimise carcass composition. Feed compoimders therefore formulate pig diets to meet the requirements for at least three amino acids (lysine, methionine -I- cystine and threonine).They will also take into accoimt the availability of certain amino acids, assessed from digestibility at the terminal Ueiun (as explained in Chapter 10). 

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. 

Plant protein sources provide 65% of the world s supply of protein, with cereal grains (47%) and pulses, nuts and oilseeds (8%) as the other major sources. Of the cereals, wheat (43%), rice (39%) and maize (12%) are the main contributors. Other limited sources of plant protein are fruits, leaves, tubers and other parts of plants included under the terms fruits, vegetables or root crops. Plant protein sources can differ from animal protein sources in terms of digestibility, amino acid composition, the presence of antinutritional (such as enzyme inhibitors) and toxic factors (e.g. saponins, cyanogens and lectins), which adversely influence protein digestibility, nutritional value and food safety. 

The membrane proteins of maize lipid bodies have been subjected to intensive studies (14). By SDS polyacrylamide gel electrophoresis (Figure 1), the proteins are resolved into several major protein bands, three of low Mr s (19,500, 18,000, and 16,500), and one of higher Mr (40,000). The low Mr proteins have alkaline pi values, and behave as hydrophobic integral proteins, as shown by their resistance to solubilization after repeated washing, amino acid composition, and partitioning in a Triton X-114 system. 

Freeze-dried DOM samples collected with the siphon-elution system (Kuzyakov and Siniakina, 2001) for the first time showed diurnal dynamics in the molecular-chemical composition of maize rhizodeposits (Kuzyakov et al., 2003). In a forthcoming study with maize, Melnitchouck et al. (2005) showed that amino acids, especially aspartic acid, asparagine, glutamic acid, phenylalanine, leucine and isoleucine contributed to the more intensive rhizodeposition during daytime than during nighttime. Furthermore, the maximum of thermal volatilization of peptides at low pyrolysis temperature in Figure 14.8 indicates the rhizodeposition or microbial formation of free amino acids rather than amino acids bound in peptides or trapped in soil humic substances. 

Figure 24. Isotopic compositions of amino acids, expressed as fractionations relative to alanine, from the vascular plants Stenotaphrum (St. Augustine grass), Helianthus (sunflower), and Borrichia (sea daisy) reported by Winters (1971) and from maize and spatterdock reported by Fogel and Tuross (1999). For comparison, the heavy gray line depicts the average of the analyses reported in Figure 14.

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