Unveiling the structural evolution and molecular assembly in ethanol-induced gelation of tamarind seed polysaccharide.

Tamarind seed polysaccharide (TSP) can form gels in the presence of ethanol, yet the underlying structural mechanism remains unclear. Here, ethanol-induced TSP gelation was investigated by combining rheology, micro-differential scanning calorimetry, atomic force microscopy, synchrotron small-angle X-ray scattering, and two-dimensional nuclear magnetic resonance. The results reveal that TSP undergoes a four-stage structural evolution during a heating-cooling cycle. At ambient temperature, ethanol reduced solvent quality and chain hydration, promoting chain association and partial precipitation. Upon heating, these initial aggregates progressively reorganized into weak, locally correlated associations that were further destabilized at elevated temperatures, yielding loosely connected structures. During cooling, reduced thermal motion and closer chain proximity promoted the reorganization of short-range associations and the formation of mechanically effective junctions, resulting in a stable gel network. These findings reveal a multistage, solvent-regulated assembly pathway for ethanol-induced TSP gelation.