Effects of Na and Ca on the rheological properties of alkaline-extracted green tea polysaccharides conjugates and their gelling mechanism.

Tea polysaccharide conjugate (gTPC) is a macromolecular conjugate in tea, whose functional properties need further exploration to expand its utilization pathways. In this study, gTPC-0.2A was extracted from green tea residues using a 0.2 wt% alkaline solution. This polysaccharide is an acidic polysaccharide containing uronic acid. The effects of Na and Ca on rheological properties of gTPC-0.2A and its gelation mechanisms were investigated. The addition of Na and Ca induced gelation of gTPC-0.2A, with rheological properties including deformation resistance, apparent viscosity, and thixotropic recovery increasing with higher metal ion concentrations. When Na and Ca concentrations exceeded 0.160 M and 0.008 M, respectively, these rheological characteristics of both gels diminished. Gelation studies indicated that electrostatic interactions, hydrogen bonding, and hydrophobic interactions were the primary driving forces for gTPC-0.2A gel formation. Appropriate metal ion concentrations promoted a denser, more stable network structure and enhanced thermal stability, whereas excessive ion concentrations disrupted these properties and weakened interactions. The findings demonstrate that adding optimal concentrations of Na and Ca can enhance the rheological properties of gTPC-0.2A aqueous solutions and induce gel formation. This research highlights the potential of tea polysaccharides as novel gel materials with promising applications in functional foods, biomedicine, and related fields.