EFFECT OF BEAN (PHASEOLUS VULGARIS) ALBUMINS ON PHASEOLIN IN-VITRO DIGESTIBILITY, ROLE OF TRYPSIN-INHIBITORS

The in vine digestibility of albumin proteins from Phaseolus vulgar's was low (26-32%) and when heated (99C/30 min) it was further reduced t o 13-18%, independent of the variety. Phaseolin (the main bean globuli n) had, after heating, a digestibility similar to casein, but when hea ted in mixtures containing as low as 10% of the albumin fraction, it s uffered a drastic decrease in its susceptibility to proteolysis. The c hemical interactions that occur among the components of the albumin fr action that reduce its digestibility do not occur between phaseolin an d albumins. Interactions between phaseolin and albumins depend on pH o f heating and are responsible for differences in molecular weight dist ribution of peptides formed by the action of pepsin, but did not alter overall digestibility of the mixture. The low digestibility indeed wa s due to heat-stable trypsin inhibitors found in the acid-soluble frac tion of the albumins. Lectins and alpha-amylase inhibitors, glycoprote ins of the albumin fraction, showed, in similar experiments, no effect on phaseolin digestibility, in spite of being very poorly digested ev en after heating.