Ultrasound-combined alkaline pH-shifting for the modification of sesame cake protein: Structural characterisation, techno-functional and antioxidant properties

Sesame protein isolate (SPI) faces challenges in food formulations due to its limited techno-functional characteristics. This research applies the effects of pH-shifting (pH 12 for 2 h) and ultrasound-combined pH-shifting (pH 12 for 2 h; 200 W at 20 kHz for 30 min) treatments, for the first time, on the structural, techno-functional, and antioxidant properties of SPI. Various analytical techniques, such as Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), X-ray diffraction (XRD), and fluorescence spectroscopy demonstrated that both pH-shifting and ultrasound-combined pH-shifting induced changes in the structure of SPI. The pH-shifting process intensified by ultrasound increased the zeta potential (−12.5 to −26.8 mV), reduced free sulfhydryl (-SH) groups (8.94 to 5.3 μmol/g), and enhanced hydrophobicity (1138 to 1273) compared to pH-shifting treatment. In addition, the highest solubility (89.33 %), improved emulsifying activity (61.41 m²/g), and foaming capacity (150 %) were observed in the sample treated with the pH-shifting process coupled with ultrasound. These results suggest that the ultrasound-combined pH-shifting process has a synergistic effect in enhancing the functional properties of proteins, particularly in foaming and emulsifying properties. The modified SPI obtained through this process could be a promising emulsifier, foaming, and gelling ingredient with the desirable antioxidant properties for the enrichment of foods.