Effects of ultrasound treatment on physicochemical and emulsifying properties of whey proteins pre- and post-thermal aggregation

The aim of this study was to determine the effect of high intensity ultrasound on physicochemical and emulsifying properties of thermally aggregated whey proteins. Whey protein isolate (WPI) solutions were sonicated for 20 min using an ultrasonic probe (frequency: 20 kHz; amplitude: 20%) pre- and post-thermal treatment (85 °C for 30 min). Changes in particle size, zeta-potential, surface hydrophobicity, free sulphydryl group content, turbidity, thermal denaturation properties, rheological properties, and emulsifying properties were studied. Soluble aggregates prepared with ultrasound treated post-thermal aggregation resulted in significantly smaller particle size and broader size distribution compared with those prepared by untreated or ultrasound treated pre-thermal aggregation (P < 0.05). It was suggested that surface hydrophobicity of the soluble aggregates was significantly increased by ultrasound applied post-thermal aggregation (P < 0.05). There was a significant reduction in turbidity of whey protein solutions by ultrasound applied post-thermal aggregation (P < 0.05). The apparent viscosity of whey protein soluble aggregate model systems has been decreased significantly by ultrasound pre- and post-thermal aggregation (P < 0.05). Emulsion activity index and emulsion stability index of soluble aggregates were increased significantly by ultrasound applied post-thermal aggregation (P < 0.05). There were no significant changes in zeta-potential, total free sulphydryl group by ultrasound either pre-or post-thermal aggregation (P > 0.05). We conclude that ultrasound treatment on post-thermal aggregation has improving effect on physiochemical and emulsifying properties of whey protein soluble aggregates for potential industrial applications.