Protein digestibility and protein quality of common beans (Phaseolus vulgaris) fed alone and with maize, in adult humans using a short-term nitrogen balance assay.

Various experiments using young human adults were carried out to measure the protein digestibility of common beans, fed alone and in different forms and fed together with maize as tortillas. In all, 36 young men were used. Common bean protein digestibility was significantly lower than that observed from meat, and similar to the digestibility of a textured vegetable protein soy protein product. It was also observed that forms of consumption may affect protein digestibility of beans. Using a short-term multiple intake protein quality assay method, it was found that feeding beans alone, N equilibrium was reached with an intake of 114 mg N/kg/day, while when fed with maize in a 87:13 ratio, N equilibrium was reached with 98 mg N/kg/day. This was attributed to both a complementary protein effect and an increase in protein digestibility.