Heat-induced denaturation impairs digestibility of legume (Phaseolus vulgaris L and Vicia faba L) 7S and 11S globulins in the small intestine of rat

7S globulin from common bean (Phaseolus vulgaris L) and 11 S globulin from faba bean (Vicia faba L) were isolated to over 90% purity and the digestibility of the proteins, either in native or denatured (120 degreesC, 20 min, 1 atm.) state, was tested in the small intestine of growing rats in acute (1 h) experiments. Native globulins were well digested (92 and 95% for 7S and 11S proteins, respectively). However, after thermal denaturation, protein digestibility of 7S globulin was reduced to 88%, while that of 11S globulin to only 79%. SDS-PAGE revealed that high amounts of the intermediate proteolytic products of phaseolin (MW 22000-27000 Da) were present in the small intestine of rats after 1 h digestion of the denatured 7S globulin, while protein material in the high MW range (>55000 Da) were recovered from the 11S globulin. The overall negative charge of unavailable proteins from the 7S globulin was found by anion exchange-FPLC separation to be higher than that of products from the 11S globulin. MALDI-MS analysis of proteins in the small intestine confirmed the presence of half-size phaseolin subunits (MW 23 700 Da) as breakdown products from the denatured 7S globulin, and of highly hydrophobic basic subunits (MW 20 000 Da) from the 11S globulin. (C) 2004 Society of Chemical Industry.