Formation mechanism of "spiderweb-like" soy protein gel co-mediated by Maillard reaction and fermentation

The aim of this study was to investigate the effect of Maillard reaction (MR) and Lactobacillus casei fermentation on the network formation mechanism and structural properties of soybean protein gel (MFP). To achieve this, interaction force analysis, texture profile analysis, moisture distribution assessment, scanning electron microscopy (SEM), and multi-parameter rheological evaluations were employed. Results showed that after 8 h of heating, the grafting degree stabilized, and soy protein isolate (SPI) particle aggregation was most evident by covalent bond aggregation. Disulfide and hydrogen bonds significantly increased (P < 0.05), while hydrophobic interactions decreased. SEM showed that extracellular polysaccharides and other fermentation products, MR products and SPI skeleton formed a closely interconnected "spiderweb-like" network structure. Texture profile analysis, water-holding capacity, and low-field nuclear magnetic resonance indicated that hardness, springiness, and water retention improved with prolonged MR time, peaking at 8 h (103.20 ± 11.32 g, 3.89 ± 0.28, 82.83 ± 2.77%) alongside uniform water distribution. Rheological assessments demonstrated enhanced network continuity, with yield stress increasing from 123.83 Pa to 209.47 Pa. Lissajous curves in the nonlinear viscoelastic region revealed reduced energy dissipation, improved structural stability, and strain stiffening over time. These findings offer insights for optimizing soy protein processing and developing innovative food products.