Conjugation of soybean protein isolate with xylose/fructose through wet-heating Maillard reaction

The conjugates of soybean protein isolate (SPI) with xylose and fructose were prepared via Maillard reaction by wet heating at mass ratio 4:1 and 80 °C for several hours. Absorbance at 420 nm indicated the existence of an induction period for the Maillard reaction between SPI and the two monosaccharaides and xylose was more reactive than fructose. SDS–PAGE and thermogravity analysis confirmed the occurrence of Maillard reaction. Fluorescence analysis revealed that the Maillard reaction led to relaxed structure for SPI in the conjugates. The conjugation with the two monosaccharaides significantly improved the solubility, but decreased the emulsifying activity of SPI. ζ-Potential measurement showed that the reaction changed the charge density of SPI and the specific effect depended on the sugar type and reaction degree. It is concluded that the wet heating-induced Maillard reaction with monosaccharaides might be a promising way for SPI modification due to shortened reaction time, improved solubility and tailored charge density.