The effects of pH and high hydrostatic pressure on the physicochemical properties of a sweet potato protein emulsion

The effect of high hydrostatic pressure (HHP) treatments on the physicochemical properties of sweet potato protein (SPP) emulsions at three pH values (3, 7 and 8) was investigated. The emulsifying activity index (EAI) and the emulsifying stability index (ESI) of all emulsions at the different pH values were significantly increased by the HHP treatments (P < 0.05). The oil droplet sizes were significantly decreased, whereas the volume frequency distribution of the smaller droplets was markedly increased when the pressure was increased from 200 to 600 MPa (P < 0.05). A significant increase in the interfacial protein concentration in the pH 3, 7 and 8 emulsions was observed when the pressure was increased from 200 to 600 MPa (P < 0.05). Under non-reducing conditions, higher molecular weight aggregates formed by disulfide bonds were observed in the pH 7 emulsions by SDS-PAGE. However, HHPs did not change and/or displace the main electrophoretic bands of SPP. The SPP emulsions had shear-thinning behaviors at pH 3 and 7 with and without HHP treatment, whereas a Newtonian behavior was observed in the pH 8 emulsion subjected to the 200 and 400 MPa treatments. These results suggest that HHP-treated emulsions stabilized by SPP could have various applications in the food industry.