Nutritive value of navy beans (Phaseolus vulgaris)

Abstract

Navy beans (P. vulgaris) were finely ground and heated in the autoclave at 121 for various lengths of time. The bean flours were offered to rats and analyzed for hemagglutinating and trypsin inhibitor activities. Effect on rat growth of progressive replacement of casein with raw or auto-claved (5 min.) bean proteins, of supplementation of beans with amino acids and trypsin, and of soaking were determined. The original observation of Everson and Heckert that raw navy beans were "toxic" to rats and that autoclaving the beans at 121[degree] for 5 min. destroyed the toxic effects has been confirmed. Longer heating periods were detri-mental. Autoclaving also destroyed the trypsin inhibitor and he mag-glutinin present in the beans. Raw beans did not support the growth of rats even when supplemented with all the amino acids in which the diet was believed deficient. Rats fed on autoclaved beans supplemented with methionine alone or with all these amino acids grew as well as those fed on the casein diet. The growth of rats receiving raw bean diets was not improved by the addition of trypsin supplements. A level of 2.0% and especially a level of 3.0% of a trypsin powder was "toxic" to the rats fed on an autoclaved bean diet. Soaking before autoclaving did not improve the growth-promoting effect of navy beans. The low nutritive value of navy beans appears to be due to a methionine deficiency and the prescence of a heat-labile "toxic" factor(s).