Assessment of the protein quality of a new high-protein soybean cultivar by amino acid analysis

The contents of total protein, amino acids, and 4-hydroxyproline-rich glycoproteins of a widely grown soybean cultivar, Maple Arrow, and a newly released high-protein genotype, OT89-16, developed by back crossing to Maple Arrow, were compared as potentially useful and practical indices for evaluating their protein quality. The significant increase (P 0.01) in protein from 33.7% (cv. Maple Arrow) to 42.1% (cv. OT89-16) and the respective decrease in methionine of 9.9% suggest that a large increase in protein was accompanied by a small but not significant decrease in the most limiting essential amino acid. Both cultivars contained an excellent balance of essential amino acids (EAA) limited only in methionine, followed by tryptophan, and their amino acid scores, adjusted for digestibility, were almost as high as those of milk and egg proteins. Mean values for total EAA(7) and EAA(10) ranged from 33.7 to 35.4% and from 46.1 to 47.8%, respectively, and both had mean calculated PER values of 2.7. The 4-hydroxyproline glycoproteins found in the extracellular matrices of soybean seeds ranged from 2.98 to 2.32 g/kg of total protein in Maple Arrow and OT89-16, respectively, which corresponded to 0.10% on a dry weight basis