Effects of sodium chloride, phytate and tannin on in vitro proteolysis of phaseolin

Abstract

Native phaseolins isolated from the Great Northern bean ( Phaseolus vulgaris L.) and the tepary bean ( Phaseolus acutifolius L.) were resistant to TPCK-trypsin, TLCK-chymotrypsin, and pepsin proteolysis in vitro. Sodium chloride (1 M) significantly decreased the initial rate of in vitro. proteolysis of both phaseolins. However, moist heat (30 min, 100 °C) denaturation of the phaseolins facilitated complete in vitro. proteolysis by all the proteinases tested. Added phytate (phaseolin:phytate ratios 10:1, 5:1, and 1:1; w w ) decreased the initial in vitro. proteolysis rates of the Great Northern bean phaseolin (GNP) by chymotrypsin and pepsin (but not trypsin) and that of the tepary phaseolin (TP) by pepsin (TP:phytate ratios 5:1 and 1:1, w w ). Tannin addition decreased the initial rate of in vitro. proteolysis of both phaseolins digested with chymotrypsin (phaseolin:-tannin ratios 100:1 and 50:1, w w ) and TP digested with pepsin (TP:tannin ratio of 10:1, w w ). This inhibitory effect of added phytate and tannin was lower than the inhibitory effect of 1 M sodium chloride. Since moist heat denaturation was able to overcome the inhibitory effect of sodium chloride, the inhibitory effects of added phytate and tannin should not impede in vitro. phaseolin proteolysis.