Soybeans, amino acid availability

Little information is available regarding potential nutrient interaction and amino acid availability in soybeans. Bau and Debry (55) have investigated how other nutrients in a product could affect amino acid availability. Attempting to refine the protein from germinated and ungerminated soybean. 

Our study successfully demonstrated that increases in ethanol production and increases in protein level of HDG can be achieved with less severe pretreatment of DG and subsequent fermentation of the pretreated DG to produce HDG. The HDG residue had a crude protein content near 61 wt%, comparing favorably with soybean meal, which has a range of 44-52 wt%. The total amount of digestible amino acids available to turkey poults in HDG was comparable to NRC feeds (26), with the exception of the levels of lysine. 

Although these amino acids act as precursors of lysinoalanine, their enzymatic release was not uniformly decreased after treatment. In fact, 4- or 8-hour alkali treatment markedly increased the release of lysine in both proteins, especially rapeseed. Serine liberation was not affected in rapeseed, but significantly decreased in soybean. These variations in amino acid availability were more marked in the first stages of digestion. They tended to disappear with time in treated and untreated proteins. 

Nitrogen sources include proteins, such as casein, zein, lactalbumin protein hydrolyzates such proteoses, peptones, peptides, and commercially available materials, such as N-Z Amine which is understood to be a casein hydrolyzate also corn steep liquor, soybean meal, gluten, cottonseed meal, fish meal, meat extracts, stick liquor, liver cake, yeast extracts and distillers solubles amino acids, urea, ammonium and nitrate salts. Such inorganic elements as sodium, potassium, calcium and magnesium and chlorides, sulfates, phosphates and combinations of these anions and cations in the form of mineral salts may be advantageously used in the fermentation. 

Stillings and Hackler (54) studied the effects of the tempeh fermentation, the action of Rhizopus oligosporus on dehulled, soaked, and sterilized soybeans. The PER of tempeh reached its peak after 24 hours fermentation and then dropped. They ascribed the changes to an increase and then a decrease in tryptophan chemically present. The PER decrease after 24 hours was also attributed to an increased quantity of mold protein, which is lower in sulfur amino acid concentration than the original soy protein. Free amino acids increased markedly, presumably due to the action of the mold proteolytic enzymes. Free methionine was present in the largest amount, and as such was highly available, thus partially accounting for the initial increase in PER. 

Ingredients (g/kg) Starter 180g/kg CP Finisher 140 g/kg CP peas and soybeans available Finisher 140g/kg CP peas available Single diet No supplemental amino acids... 

Enzymatic hydrolysates of various proteins have a bitter taste, which may be one of the main drawbacks to their use in food. Arai el al. [90] showed that the bitterness of peptides from soybean protein hydrolysates was reduced by treatment of Aspergillus acid carboxypeptidase from A. saitoi. Significant amounts of free leucine and phenylalanine were liberated by Aspergillus carboxypeptidase from the tetracosapeptide of the peptic hydrolysate of soybean as a compound having a bitter taste. Furthermore, the bitter peptide fractions obtained from peptic hydrolysates of casein, fish protein, and soybean protein were treated with wheat carboxypeptidase W [91], The bitterness of the peptides lessened with an increase in free amino acids. Carboxypeptidase W can eliminate bitter tastes in enzymatic proteins and is commercially available for food processing. 

Tt is well recognized that the nutritional value of dietary proteins de-pends primarily on the content of their constituent amino acids, especially of their essential amino acids. Because of deficiencies of lysine and methionine, and to a lesser extent of a few other amino acids, proteins from plants and other alternative sources have low biological quality. Moreover, incomplete digestion of the protein also may result in a lack of complete availability (I) of the essential amino acids and may further reduce its value. In many raw plant foodstuffs such as soybeans, common beans, or unprocessed protein foods, undenatured... 

Such chemical changes may lead to compounds that are not hydrolyzable by intestinal enzymes or to modifications of the peptide side chains that render certain amino acids unavailable. Mild heat treatments in the presence of water can significantly improve the protein s nutritional value in some cases. Sulfur-containing amino acids may become more available and certain antinutritional factors such as the trypsin inhibitors of soybeans may be deactivated. Excessive heat in the absence of water can be detrimental to protein quality for example, in fish proteins, tryptophan, arginine, methionine, and lysine may be damaged. A number of chemical reactions may take place during heat treatment including decomposition, dehydration of serine and threonine, loss of sulfur from cysteine, oxidation of cysteine and methio-... 

Factors which affect the rate and extent of enzymatic hydrolysis of proteins include (1) the substrate specificity of the enzymes, (2) modification of the amino acid side chains of the substrate proteins, and (3) the three-dimensional structure of the substrate proteins. It is essential that the active center of the enzymes be able to bind with specific amino acid residues of the substrate protein. The native soybean protein molecules are completely folded and therefore the specific amino acid residues required by the enzymes may not be available. This is why native... 

Another protein in soybeans that is destroyed by extrusion is the trypsin inhibitor, which is produced in the pancreas. Without the action of trypsin, the animal cannot use protein, as it is trypsin that splits or hydrolyzes the protein molecule. Other less important enzyme inhibitors that are denatured by the extruder relate to fats and the carbohydrate fraction of a diet. As the heat needed to deactivate enzymes is less than that needed to prepare oilseeds for oil extraction, the effect on the amino acids is much less severe, thus making them more available to the animal or higher in digestibility. 

This section on chemical factors related to quality in soybeans is divided into subparts on protein and oil, fatty acids, amino acids, tests for protein, carbohydrates and sugars, and other factors that are often discussed, particularly as soybeans are enhanced for more specific end uses. The other factors include tests for fiber, phosphorus, to-copherols, and isoflavones. The intent is to discuss the importance of these factors, to provide background, and, because of increased use of near-infrared spectroscopy as a measurement method for whole and ground soybeans, to include that technology in the discussion of test measurements. While many primary and other methods for measuring these chemical factors are available, this chapter does not intend to cover those methods. 

In comparison with the mean release of other amino acids (total N), LAL was less readily hydrolyzable. Its capacity of enzymatic release varied from 25 to 43% of that of other amino acids. LAL was more available (i.e. digestible) from rapeseed than from soybean this availability increased with LAL content in rapeseed, and decreased with LAL content in soybean. 

Table II shows the effect of alkali treatment on some other amino acid digestibility. The hydrolytic release rate for individual amino acids was different from the mean rate of release for protein nitrogen and varied according to the protein. For example, lysine from rapeseed protein was liberated slowly. Lysine was more available from soybean protein and its release rate was equivalent to that of serine. The latter amino acid is equally available from both protein sources.

Heating can also have favorable effects. Heating soybean flour improves the utilization of protein by making the amino acid methionine more available, and heating raw soybeans destroys the inhibitor of the protein digestive enzyme trypsin. Cooking eggs destroys the trypsin inhibitor ovomucoid in the white. 

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