Relationship between content and intake of bean polyphenolics and protein digestibility in humans

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Abstract
The purpose of this study was to determine the effect of bean polyphenolics on bean protein digestibility in humans. Steam pressure cooking decreased tannic acid in beans by: 38.2 (white), 23.9 (red), 38.5 (white:black mixture, 50:50), 20.5 (Ipala black) and 44.4% (Jalpatagua black). The reduction in catechin was: 57.5, 97.6, 83.0, 78.7 and 88.4%, respectively. The content of tannic acid in dried cooked beans was: 284.9 in white, 834.5 in red, 620.2 in the white:black mixture, 1,021 in Ipala black and 1,009 mg/100 g in the Jalpatagua black bean. These percentages correlate significantly with fecal nitrogen (r=0.29, p<0.05). Catechin of the dried cooked beans was 7.5 in white, 27.4 in red, 25.4 in the white:black mixture (50:50), and 60.1 and 55.5 mg/100 g in each of the black cultivars, and correlated significantly with fecal nitrogen (r=0.34, p<0.01), absorbed nitrogen (r=−0.37, p<0.01) and protein digestibility (r=−0.35, p<0.01). It was concluded that one of the factors that reduces bean protein digestibility is the polyphenlic compound.