Influences of pH-regulated metal phenolic networks on soy protein hydrolysate nanofibril gels: Microstructure, rheological properties and thermal stability

Metal-phenolic networks (MPNs) are widely used to improve the structure, mechanical properties and stability of gels. In this study, tannic acid (TA) was coordinated with metal ions (Mn 2+ and Zn 2+ ) under pH conditions of 2.0, 5.5, and 8.0 to form MPNs, which subsequently induced soy protein hydrolysate nanofibrils (SPHN) to produce gels (SPHN-MPNs gels). As the pH increased, the coordination interactions between TA and Mn 2+ /Zn 2+ became progressively stronger, as reflected by the emergence of new charge-transfer–related absorption features. Spectral analysis confirmed that MPNs could promote gel cross-linking via hydrogen bonds and metal ions coordination interactions between MPNs and SPHN. Gels induced by MPNs displayed a denser gel structure as the pH increased, resulting in higher storage modulus and elevated thermal transition temperature. MPNs formed between TA and Zn 2+ at pH 8.0 imparted higher G′ values and a faster recovery rate to the gels after four shear-stress cycles. These findings will expand the potential applications of SPHN-MPNs gels in the food industry.