Effect of Lycium barbarum polysaccharides on heat-induced gelation of soy protein isolate

As a versatile ingredient, soy protein isolate (SPI) has been widely used in the food industry and the gelling property of SPI can be further modified using exogenous polysaccharides to achieve desired functionalities and nutritional properties. Therefore, in this study, the effect and mechanism of Lycium barbarum polysaccharides (LBP) on the gelling behavior of soy protein isolate (SPI) were investigated. It was found that the gel strength, water-holding capacity, and viscoelastic properties of SPI gel were improved with the addition of LBP (0.5-2.5%, w/v) in a concentration-dependent manner. Thermogravimetric analysis indicated that the thermal stability of SPI was also improved with the addition of LBP. The FTIR spectroscopy revealed that LBP addition had no significant effect on the a-helix and random coil content of SPI but significantly increased the 8-sheet content and reduced the 8-turn content. Furthermore, through intrinsic fluorescence, surface hydrophobicity, free sulfhydryl content, and protein solubility analysis, it was concluded that the electrostatic and hydrophobic interactions played a critical role in the formation of the SPI-LBP gel composite. Interestingly, the disulfide bond formation was the least contributor to the binary gel composite network. Overall, LBP is not only an important nutritional supplement but also a promising functional ingredient for improving the gel properties of SPI.