Effects of different ph on properties of heat-induced Auricularia auricula-judae polysaccharide-whey protein isolate composite gels

The purpose of this study was to investigate the effects of different pH conditions on the properties of heat-induced composite gels of Auricularia auricula-judae polysaccharide (AP) and whey protein isolate (WPI). The color, hydration properties, texture, thermal stability, rheological properties, sulfhydryl content, surface hydrophobicity, and microstructure of the gels were evaluated. Due to the Maillard reaction, the color of the gel changed from white to brown with increasing pH. In contrast to the trend observed for color, the gels formed at pH 8 had better water holding capacity, springiness, hardness, thermal stability compared to pH 4, pH 6, and pH 10. Furthermore, rheological measurements showed that the gels after different pH treatments maintained their morphology by non-covalent interactions (hydrophobic interactions and electrostatic interactions), the gels exhibited shear thinning behavior. The free sulfhydryl content and surface hydrophobicity of the gels further confirmed the contribution of hydrophobic interactions in the gel network. The observation of the microstructure showed that the gel changed from a granular gel with rough surface to a gel with uniform and smooth surface with the increase of pH. This study provides some basic data references for improving the properties of AP-WPI composite gels and developing new gel-type products.