Effect of ultrasound on heated soybean isolate protein-soybean oligosaccharide glycation conjugate acid-induced emulsion gels and their applications as carriers of zeaxanthin

The acid-induced emulsion gels were prepared by heated soybean isolate protein (HSPI)-soybean oligosaccharide (SOS) glycation conjugates with ultrasonic treatment at 200 W for 10, 20 and 30 min, which were used as carriers of zeaxanthin. The structural characteristics of HSPI-SOS conjugates, the properties of conjugate emulsion gels and the delivery for zeaxanthin were investigated. The appropriate ultrasound increased glycation degree between HSPI and SOS, and inhibited the formation of browning products, leading to more disordered secondary structure and less compact tertiary conformation of conjugates, which promoted the exposure of hydrophobic groups, the reduction of free sulfhydryl groups and the enhancement of thermal stability. The ultrasonic HSPI-SOS conjugate emulsion gels exhibited smoother and denser microstructure with smaller and more evenly distributed oil droplets, which improved gel hardness, water holding capacity and rheological parameter, resulting in the reinforcement of physical stability of conjugate emulsion gels during heat and pH treatment. Furthermore, the ultrasonic treatment enhanced the chemical stability of zeaxanthin encapsulated in conjugate emulsion gels under light treatment and delayed the chemical degradation of zeaxanthin, which indicated that the ultrasonic treatment facilitated the protective effect of conjugate emulsion gels on zeaxanthin. The bioaccessibility of zeaxanthin encapsulated in conjugate emulsion gels was improved by ultrasonic treatment. Therefore, ultrasound-glycation treatment could be used to modify the structure of proteins to improve the physicochemical stability of conjugate emulsion gels, which exhibited excellent application potential in the encapsulation, protection and delivery for zeaxanthin.