Amino Acid Balance is Affected by Protein Concentration in Soybean

Soybean [Glycine max (L.) Merr.] produces a high-quality protein that provides an appropriate balance of amino acids for monogastric animals. It has been reported that the relative abundance of some essential amino acids may be reduced in soybean with high protein concentration. A dilution of essential amino acids in soybean protein would lead to a reduction in the value of that protein to the end user, and undefined variation in amino acid balance of soybean would lead to poorly balanced animal rations. The objective of this work was to determine whether amino acid balance is affected by seed protein concentration and to characterize any putative changes in the relative abundance of each amino acid across a range of soybean protein concentrations. We created a wide range of protein concentrations in soybean seed by imposing managed stress treatments previously shown to lower or raise protein concentration. We found that the amino acid composition of soybean protein was affected by protein concentration. The relative abundance of amino acids that are often limiting for animal growth, such as lysine, methionine, cysteine, tryptophan, and threonine, were reduced with increasing seed protein concentrations, whereas arginine and glutamic acid were increased. However, treatments used in this study uncovered a potential role for the availability and source of reduced C and N to impact the relative abundance of each amino acid independently, highlighting the complexity of this interrelationship.