PARTIAL REDUCTION OF SOY PROTEIN ISOLATE DISULFIDE BONDS

Partial reduction of disulfide bonds of soy protein isolates was followed electrophoretically. Isolates treated with Na2SO3 under different conditions showed disappearance of high molecular weight aggregates. Acidic and basic 11S polypeptides and some whey proteins that remain in the isolates were also affected; reduction of the AB-11S subunit was very limited. The sulfitolysis method was also studied. The addition of a catalyst (Cu) and oxygen showed a similar effect in the sulfitolysis of soy proteins with Na2SO3. To achieve complete sulfitolysis, the presence of a denaturing and an oxidizing agent were needed. Mainly AB subunits of glycinin were reduced when urea was used, while mostly components other than AB-11S subunits were reduced when Na2SO3 was used in the presence of Cu and/or oxygen.