Emulsifying properties of high pressure treated soy protein isolate and 7S and 11S globulins

The influence of high pressure (HP) treatment (200–600 MPa) on the emulsifying activity index (EAI) and emulsifying stability index (ESI) on the 7S and 11S globulins and soya protein isolate (SPI) at pHs 7.5 and 6.5, at different concentrations (0.25–0.75%) was studied. Solubility and surface hydrophobicity were used as indices of the degree of denaturation caused by HP. 7S showed the highest EAI and surface hydrophobicity after treatment at 400 MPa, whereas 11S showed its highest EAI and surface hydrophobicity after treatment at 200 MPa. No significant correlation (P>0.05) was found between solubility and EAI or hydrophobicity. SPI showed the optimum value of EAI after treatment at 400 MPa although its surface hydrophobicity was low. It is suggested that pressure at 400 MPa dissociated the 7S of the SPI into partially or totally denatured monomers that enhanced the surface activity but at the same time, the unfolding of the polypeptides of the 11S within the hexamer led to aggregation, negatively affecting the surface hydrophobicity of the SPI. The ESI values for the non-treated samples of SPI, 7S and 11S were higher at lower concentrations. At the same pH and concentration, the ESI decreased with increasing HP, except for the 7S at pH 7.5 and a protein concentration of 0.75%.