SOY PROTEIN ISOLATE COMPONENTS AND THEIR INTERACTIONS

The electrophoretic behavior of a soy protein isolate was analyzed in both nonreducing and reducing SDS-PAGE. Aggregates formed by alpha and alpha' subunits of beta-conglycinin exhibited both ionic interactions and disulfide bonds. Higher molecular weight aggregates (180 000-190 000) consisted of trimers or dimers of alpha' and alpha subunits, wher eas those of intermediate molecular weight (115 000-120 000) were form ed by alpha',alpha subunits of beta-conglycinin and A polypeptides of glycinin. The latter exhibited a higher sensitivity toward changes of ionic strength and thermal treatments. The proportion of alpha' and al pha subunits of the isolate which was included in these aggregates is highly dependant on the freeze-drying conditions. These aggregates wer e readily reduced in the presence of Na2SO3, even at low concentration s and in the absence of denaturing agents, thus suggesting that the di sulfide bonds involved were accessible. These aggregates were stable a t different pH values, in the presence of both SDS and urea.