Alcalase rapeseed inhibitors: Purification and partial characterization

Extensive rapeseed protein hydrolysate obtained sequentially with Alcalase and Flavourzyme showed inhibitory activity towards Alcalase. Inhibitory act ivity decreased as the hydrolytic process progressed probably by heat denat uration and/or partial protease degradation, Alcalase rapeseed inhibitors were purified by gel filtration and subsequent ion exchange chromatography. They are composed of peptides of 8.4 and 6.1 kDa linked by interchain disulphide bonds, as observed by reducing SDS-PAGE , with a native molecular weight of 18 kDa, Aminoacid composition of the in hibitors was characterized by the high proportion of methionine (4.2%) and cysteine (4.6%). Alcalase inhibitors were partially resistant to heat treat ment; after heating at 70 degreesC for 45 minutes more than 50% of the orig inal inhibitory activity remained in the purified protein but after heating at 90 degreesC for 5 minutes, inhibitory activity decreased very fast to a basal level. The possible relation of these protease inhibitors with the 2 S albumin storage proteins is discussed.