Effects of high pressure on functional properties of soy protein

Simultaneous measurement of the effects of low soy protein concentration, pH and high pressure treatment at room temperature on solubility, emulsifying properties and rheological properties (loss modulus, G″) of soy protein isolate (SPI) were evaluated. Central composite rotatable designs (23) were employed over two pH ranges (2.66–4.34 and 5.16–6.84) with SPI concentration (0.32–3.68%) and pressure (198–702 MPa) as the other independent variables. The surface responses were obtained for protein solubility, emulsifying activity index (EAI) and G″. The samples with the highest effect on protein solubility, EAI and G″ values were evaluated, as well, by electrophoresis and free sulphydryl determination. The pH was the main factor that affected protein solubility, with solubility at a maximum at pH < 3 or pH > 6. Increasing SPI concentration and decreasing/increasing the pH away from the isoelectric point both caused a reduction in EAI. Loss modulus (G″) was found to increase with SPI concentration in both pH ranges.