Gelation of xyloglucan by addition of epigallocatechin gallate as studied by rheology and differential scanning calorimetry.

Interaction of tamarind seed xyloglucan (TSX) and epigallocatechin gallate (EGCG) was investigated. TSX alone showed the rheological behaviors of dilute and semidilute solution types in the temperature range from 10 to 50 degrees C and the concentration range from 1 to 10%. Addition of a small amount of EGCG changed the rheological properties of TSX solutions to induce a thermoreversible gelation. The sol-gel transition was detected as a crossover of the storage and loss shear moduli at a certain temperature in thermal scanning rheological measurements and an endo- and exo- thermic peaks in curves obtained by differential scanning calorimetry on heating and cooling. High storage modulus of the gels at all experimental frequencies also indicated the formation of a network structure. Increase in the gel strength and the enthalpy of the transition with increasing EGCG concentration at fixed TSX concentration suggested that EGCG was directly involved in the network formation through association with TSX. The TSX gel was obtained by addition of appropriate amount of EGCG. Addition of an excessive amount of EGCG induced precipitation.