Xyloglucan gelation induced by enzymatic degalactosylation; kinetics and the effect of the molar mass.

Gelation kinetics of aqueous solutions of xyloglucan (XG) extracted from H. courbaril seeds were investigated, in-situ, during enzymatic removal of galactose units by oscillatory shear rheological measurements, at different XG and enzyme (β-galactosidase) concentrations. Increasing the enzyme concentration (C enz ) led to an increase of the gelation rate. Master curves of the evolution of the storage shear modulus at different C enz could be formed by time-C enz superposition showing that C enz influenced the kinetics, but not the gelation process and the final gel stiffness. The behaviour of gels formed by XG with different molar mass (M w ), prepared by endoglucanase hydrolysis, was evaluated as a function of the temperature. It was found that cooling led to a decrease of the crosslink density causing a decrease of the gel stiffness. The decrease of the crosslink density was sufficient to depercolate the network formed by relatively small XG with M w = 10 5 g mol −1 , but gels formed by XG with M w ≥ 8 × 10 5 g mol −1 persisted down to 10 °C. It is shown that the melting temperature and the gel stiffness at high temperatures can be controlled independently by varying the molar mass and the concentration of XG chains. [ABSTRACT FROM AUTHOR]