Ultrasonic pretreatment improved the physicochemical properties and riboflavin delivery ability of transglutaminase-catalyzed soy protein isolate gel

Soy protein isolate (SPI) was pre-treated with ultrasonic (400 W, 30-120 min) and then formed gel using transglutaminase (TG) method. Effects of ultrasonic pretreatment on structural, rheological and thermal properties as well as riboflavin delivery ability of SPI gel were investigated. Ultrasonic treatment significantly decreased the particle size, increased the free sulfhydryl content, enhanced the surface hydrophobicity, unfolded the conformational structure of SPI, facilitated the disulfide bonds and epsilon-(gamma-glutamyl) lysine isopeptide bonds formation in transglutaminase-catalyzed soy protein isolate gel (TCSG). Ultrasonic pretreatment, particular for 60 min, significantly enhanced the gel strength, storage modulus, loss modulus, consistency and thermal stability, but decreased the flow behavior index of TCSG. The TCSG without ultrasonic pretreatment showed a nonuniform gel network with large and irregular pores. When applied ultrasonic pretreatment, more dense, uniform and stable gel networks were developed. The above physicochemical properties improvements inhibited the swelling behavior and markedly enhanced the riboflavin encapsulation efficiency and riboflavin delivery ability of TCSG, leading to 81% of riboflavin released in simulated intestinal environment. Therefore, ultrasonic pretreatment could be an efficient approach to improving the gel properties and nutrients delivery ability of SPI gel.