Combined effect of ultrasound and charge on the complexation of soy protein isolate and κ-carrageenan and their emulsion properties

This study aimed to formulate a safe and stable oil-in-water emulsion. Emphasis was placed on the effects of ultrasound and charge on the formation and emulsifying properties of soy protein isolate/κ-carrageenan (SPI/κ-Car) complexes. Results from the various ultrasonic modes showed pretreatment of SPI with energy-gathered ultrasound (EU) significantly enhanced the hydrophobicity index and emulsion creaming index of the SPI/κ-Car complexes. The optimization results showed that the most pronounced effects were achieved with an ultrasonic power of 150 W and a treatment time of 15 min. Under these conditions, the hydrophobicity index of the complexes elevated to 3056.4, while the emulsifying activity index reached 11.2 m 2 /g, corresponding to increases of 227.4% and 38.3%, respectively, compared to the control. A combination of ultrasound with pH 6.0 or 25 mM NaCl effectively modified the charge density and promoted the formation of SPI/κ-Car complexes. Ultrasonic treatment combined with pH 6 (U-pH 6) resulted in the maximum values of emulsifying activity index and emulsion stability index, reaching 13.4 m 2 /g and 135.8, respectively. A synergistic treatment of ultrasound, pH 6.0 and 25 mM NaCl (U-25 mM-pH 6) induced the exposure of more hydrophobic groups, resulting in the lowest creaming index of emulsion after 7 days of storage. These findings suggest that ultrasound combined with charge treatment offers a promising method for optimizing the emulsifying properties of SPI/κ-Car complexes.