Physico–chemical aspects of galactoxyloglucan from the seeds of Hymenaea courbaril and its tetraborate complex

A galactoxyloglucan hydrocolloid (HXGRP) (Glu:Xyl:Gal molar ratio, ∼4:3:1) was obtained from cotyledons of seeds of Hymenaea courbaril by aqueous extraction and then purified (33% yield). Rheological measurements showed that HXGRP, in aqueous systems, interacts with tetraborate ions increasing both, viscosity and G′ values, also increasing the viscoelasticity of the system, but not forming a gel, as shown by Cox-Merz experiments. This interaction dependent of the amount of sodium tetraborate and the pH, and was analyzed in terms of hindered reptation. A temperature sweep of the HXGRP-tetraborate complex showed a characteristic cleavage of cross-links between polysaccharide and borate ions at high temperatures. An aqueous solution of HXGRP after heating at 85 °C for 2 h showed a decrease in its absolute viscosity.