Condensed tannins and related phenols in 13 samples of red Guatamalan common beans (Phaseolus vulgaris) were determined by four chemical assays. The results were highly correlated although the degree of variation among the samples differed greatly according to the assay. In rat feeding trials, tannin content was negatively correlated with net protein ratio, a measure of protein quality, and positively correlated with protein digestibility. Neither correlation was statistically significant due primarily to the low tannin content of the diet. Methionine supplementation not only improves the protein quality but may also play a role in metabolic detoxification of tannin.

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