The influence of rat endogenous nitrogen excretion on the assessment of bean protein quality.

The main objective of the present work was to study the interference of rat endogenous nitrogen excretion with the assessment of digestibility and biological value of dry bean (Phaseolus vulgaris, L.) protein. Dry bean plants were cultivated under (15NH4)2SO4 fertilization and at harvest dry beans had 1.080 atoms % of 15N-excess. Nitrogen balance studies indicated that bean protein digestibility and biological value were higher when N-balance was based on 15N-excess as compared to total nitrogen, both for undenaturated and heat-denaturated protein. The 15N-balance also showed that heat treatment significantly improved (p less than or equal to 0.05) the digestibility of bean protein in the integral flour and in protein isolate while the biological value decreased for both materials. The results permitted the conclusion that the conventional methods employed for calculation of bean protein digestibility and biological value, based on total nitrogen balance and protein-free diet, underestimate these indices of protein quality.