Mechanistic insights into soy protein isolate gelation through polyphenol-cellulose pre-complex strategy: Gelation...

Protein-polyphenols-polysaccharides ternary gels face molecular binding competition leading to a compromised network integrity. This study introduces a pre-complexation strategy incorporating microcrystalline cellulose (MCC)-polyphenols (chlorogenic acid (CA), tannic acid (TA) and (-)-epigallocatechin 3-gallate (EGCG)) complexes into soy protein isolate (SPI) gels to enhance structural and functional properties. Pre-complexes were investigated and compared with sequential addition to evaluate their impact on SPI gel characteristics. The results showed that MCC-TA complex exhibited high polyphenol grafting (20.8 ± 0.39 mg/g), accompanied by new absorption peak at 1715 cm^-1 (C=O) and 1207 cm^-1 (CO), and reduced crystallinity from 78.62% (MCC) to 64.44%, reflecting high hydroxyl group density compared to MCC-EGCG and MCC-CA. Among the three complexes, MCC-TA incorporation in SPI gel significantly enhanced water holding capacity (51.68 ± 2.41%-57.83 ± 2.03%) and gel strength (15.08 ± 1.13 g - 19.31 ± 0.85 g) with increase in concentration (0.065-0.25%/SPI). Scanning electron microscope (SEM) images demonstrated that MCC-TA promoted the formation of a cohesive network, while molecular docking confirmed phenolic group (-OH) interaction with protein. Structural analysis further indicated that MCC-TA stabilized the helical conformation of SPI, increased β-sheet content and inducing blue shift in fluorescence spectra. Low-Field-NMR showed a high immobilized water fraction (T₂₂, 97.86 ± 0.43%) in SPI-MCC-TA gels, with slightly increased free water (T₂₃, 1.77 ± 0.01%) at higher concentration (0.25%/SPI), suggesting controlled water mobility that enhanced gel flexibility. These findings highlight new insight into the fabrication of ternary gel through pre-complexation that mitigates binding competition and offers a promising approach for designing protein-based structured foods with improved mechanical and functional properties.