Abstract: The effect of ultrasonic treatment at different powers on emulsifying and gelation properties and structural state of soy protein isolate (SPI)-whey protein isolate (WPI) mixture was investigated. Physicochemical properties such as emulsifying activity, emulsion stability, gel strength, water-holding capacity were studied and structural properties were characterized by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), ultraviolet (UV) spectroscopy, and scanning electron microscopy. The results showed that the maximum emulsification and emulsifying activities of SPI-WPI mixture of 76.46 m2/g and 22.83 min, respectively were obtained with 300 W ultrasonic treatment. A slight red shift in the UV-Vis absorption spectrum was observed after this treatment, indicating exposure of internal groups outside of protein molecules and protein structure changes. The gel strength and water-holding capacity of SPI-WPI mixture reached maximum values of 1 000.93 g and 87.11% at 300 W, respectively. This was consistent with the results of scanning electron microscopy, which showed that the protein gel had a dense and regular three-dimensional network structure. This study demonstrated that ultrasonic treatment was effective in improving the functional properties of SPI-WPI mixture.

Key words: soy protein isolate, whey protein isolate, emulsification, gel properties, ultrasonic