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

Abstract

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 (Cenz) led to an increase of the gelation rate. Master curves of the evolution of the storage shear modulus at different Cenz could be formed by time-Cenz superposition showing that Cenz influenced the kinetics, but not the gelation process and the final gel stiffness. The behaviour of gels formed by XG with different molar mass (Mw), 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 Mw=105gmol-1, but gels formed by XG with Mw≥8×105gmol-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.