Characterization of EGCG-concentration responsive gel of tamarind seed polysaccharide

Tamarind seed polysaccharide (TSP) can form gels through interaction with tea polyphenols, with polyphenol concentration serving as a key determinant of the resulting gel properties. This study systematically investigated the effects of (-)-epigallocatechin-3-gallate (EGCG) concentration on the phase transition and gel properties of TSP. The macroscopic properties and microstructural evolution were characterized using rheology, diffusing wave spectroscopy (DWS), and cryo-scanning electron microscopy (cryo-SEM). Results showed that TSP (1.0% w/v) exhibited sol, sol-gel transition, gel, gel-precipitation transition and precipitation states at EGCG concentrations of 0.0-0.1, 0.1-0.2, 0.2-0.8, 0.8-0.9 and 0.9-1.0% (w/v), respectively. DWS analysis revealed that the sol-gel transition temperature increased with EGCG concentration, and the network cross-linking density gradually rose during cooling. Both deformation resistance and gel strength exhibited a non-monotonic dependence on EGCG concentration, peaking at 0.4% (w/v) with a minimum deformation strain of 0.50% and a maximum gel strength of 193.69 g. Further increases in EGCG concentration promoted excessive molecular aggregation, which ultimately led to precipitation. This trend was further confirmed by cryo-SEM observations. Hydrogen bonding and hydrophobic interactions were identified as the critical molecular forces driving gelation. In conclusion, the structural properties of TSP gels can be precisely tailored by adjusting EGCG concentration. These findings establish a theoretical foundation for further applications of TSP.