Nutritional value of cooked beans (Phaseolus vulgaris) and their isolated major protein fractions

The digestibility and nutritional properties of whole cooked beans (Phaseolus vulgaris L) and their isolated and cooked major protein fractions were evaluated in rats. Isolated globulin GI was highly digestible (89.5%) but had a low NPR value (1.51). The albumins and glutelins exhibited intermediate digestibilities (79.1 and 73.2%) and a biological utilisation NPR of 3.18 and 2.91, respectively, 30% lower than casein. Whole beans exhibited the poorest digestibility (62.8%) with a faecal excretion of more than 30% of the ingested nitrogen and an intermediate NPR of 2.27. There was a direct relation between the amount of ingested dietary fibre and dry matter and N excretion. Enrichment of whole beans with the isolated albumin fraction, rich as it is in sulphur amino acids, did not improve NPR value. Dry beans apparently contain components producing undigestible protein complexes which affect amino acid availability and increase endogenous nitrogen excretion.