Effect of Mono- and Polysaccharide on the Structure and Property of Soy Protein Isolate during Maillard Reaction

As a protein extracted from soybeans, soy protein isolate (SPI) may undergo the Maillard reaction (MR) with co-existing saccharides during the processing of soy-containing foods, potentially altering its structural and functional properties. This work aimed to investigate the effect of mono- and polysaccharides on the structure and functional properties of SPI during MR. The study found that compared to oat β-glucan, the reaction rate between SPI and D-galactose was faster, leading to a higher degree of glycosylation in the SPI–galactose conjugate. D-galactose and oat β-glucan showed different influences on the secondary structure of SPI and the microenvironment of its hydrophobic amino acids. These structural variations subsequently impact a variety of the properties of the SPI conjugates. The SPI–galactose conjugate exhibited superior solubility, surface hydrophobicity, and viscosity. Meanwhile, the SPI–galactose conjugate possessed better emulsifying stability, capability to produce foam, and stability of foam than the SPI–β-glucan conjugate. Interestingly, the SPI–β-glucan conjugate, despite its lower viscosity, showed stronger hypoglycemic activity, potentially due to the inherent activity of oat β-glucan. The SPI–galactose conjugate exhibited superior antioxidant properties due to its higher content of hydroxyl groups on its molecules. These results showed that the type of saccharides had significant influences on the SPI during MR.