Comparative study of structural characteristics and thermal behavior of whey and isolate soybean proteins

Electrophoretic profiles, sulfhydryl(SH)/disulfide (SS) groups content, and surface hydrophobicity (H-o) values of whey soybean proteins (WSP) and nat ive soy isolates (NSI) were determined WSP, composed mainly by Kunitz tryps in inhibitor (KTI), and lectin (L), has a H-o value of 24.0 +/- 1.0, which is 6.8 times lower than that of NSI ones, and SH/SS groups content in the s ame range of NSI. The thermal behavior of WSP and NSI was studied by differ ential scanning calorimetry (DSC). The WSP thermogram in water, similar to NSI, showed two main peaks (Tp values. 74.0 +/- 0.5 C and 90.4 +/- 0.8C) at tributed to thermal denaturation of KTI and L, respectively. These endother ms are slightly affected by mu, whereas those of NSI are strongly affected (Tp of 7S and 11S peaks increase 17C and 20C respectively, by increasing Na Cl concentration from 0 to 1M). WSP has low Ho values not noticeably affect ed by ionic strength changes, whereas NSI has higher Ho, that increase in s aline media and favor intermolecular hydrophobic interactions. The conseque nt low tendency to protein aggregation by hydrophobic interactions in WSP w ould explain their lower thermal stability at high mu. Control proteins of both preparations (7S and 11S enriched fractions for NSI, and purified tryp sin inhibitors, urease and lectin for WSP) were use to confirm these result s.