Bioavailability of amino acids in beans (Phaseolus vulgaris)]

Biological availability of amino acids of three common bean (Phaseolus vulgaris) varieties was evaluated in four, healthy adult subjects, consuming bean-based diets by the amino acid absorption technique and the short-term nitrogen balance method. The amino acid composition was determined according to the ionic interchange method, and tryptophan was estimated by a colorimetric procedure. The essential amino acid (EAA) and non-essential amino acid (NEAA) pattern suggests that no significant differences in content exists in the three bean varieties. When the EAA patterns were compared with those of FAO/WHO, the limiting AA in decreasing order were found to be: tryptophan, valine and threonine (sulfur AA are not considered because the hydrolysis used in this study destroys them); and the AA surpassing the reference pattern were the aromatic AA and isoleucine. Apparent (AD) and true (TD) digestibilities of the EAA fluctuated between 33 and 59% and 60 and 85%, respectively, for black beans. With red beans, these results diminished: 29 and 55% AD and 64 and 81% TD, while for white beans the limits extended: 18 and 57% AD and 36 and 86% TD. Valine proved to be the EAA of lower biological availability, and lysine and phenylalanine the most available. It is suggested that the low digestibility of valine could be due to the amino acid imbalance existing in the bean protein, since this contains an excess of isoleucine and leucine in relation to valine. The AD and TD of the AAE with respect to the NEAA were of 0.89 and 0.98 for black bean, 0.89 and 0.96 for the red and 0.77 and 0.90 for the white, which indicates that biological availability of the NEAA is higher than that of the EAA. Findings thus confirm that biological determination of the TD of protein permits prediction of the TD of the AA, since a positive correlation (r = 0.93) statistically significant was found (p less than 0.05) among them. Utilization of the TD parameter instead of that of AD to estimate the protein quality is therefore recommended.