Quality Factors Affecting the Nutritive Value of Bean Seed Protein1

Seeds of four bean (Phaseolus vulgaris L.) strains with a range in protein content from 21.5 to 31.9% were selected and analyzed for their constituent amino acids. Differences in the levels of certain essential amino acids were detected. Total methionine and microbiologically available methionine, each as percent of protein, were similar in three of the four strains, but one strain had a lower level of available methionine, suggesting that part of the total methionine was unavailable. Correlation between protein efficiency ratio (PER) for rats and available methionine as percent of protein in the four strains was positive and significant, while similar correlations between PER and total methionine as percent of protein with or without cystine were not significant. The microbial assay used in determination of available methionine levels is outlined and its value in a breeding program for improving nutritive quality of beans is discussed.