Effect of Ultrasound Combined with pH Adjustment on Gelling Properties of Ginkgo Seed Protein Isolate/Whey Protein Isolate Composite Gels

To investigate the effects of ultrasound treatment combined with pH adjustment on the gelling properties of composite gels prepared from ginkgo seed protein isolate (GSPI) and whey protein isolate (WPI), the physicochemical properties and molecular behavior of the GSPI and WPI mixture and the texture, water-holding capacity (WHC) and microstructure of the heat-induced gel of the protein mixture were characterized. Results showed that ultrasonic treatment at 25%, 45%, or 65% power alone did not significantly influence protein solubility. However, ultrasonic treatment combined with lower pH (pH 4.0) markedly decreased protein hydrophobicity, and increased surface sulfhydryl group content and the sol’s particle size. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared (FTIR) spectroscopy showed that ultrasonic treatment affected protein structure and aggregation behavior. The heat-induced composite gel formed at lower pH had poor textural properties, whereas the composite gel formed at higher pH (especially at pH 5.0) exhibited improved textural properties and higher WHC. The textural properties and WHC of the composite protein gel were significantly improved with increasing ultrasonic power, which was attributed to the fact that ultrasonic treatment strengthened the interaction between hydroxyl groups in GSPI and WPI, promoting protein aggregation and cross-linking and improving the structural compactness of the composite gel. Overall, ultrasound treatment combined with pH adjustment could be an effective method for improving the functional properties of the composite protein gel.