A natural hydrocolloid extracted from Hymenaea courbaril seeds contains Glc:Xyl:Gal:Ara in a molar ratio of 51:27:21: 1. Selective TEMPO radical oxidation (2,2,6,6-tetramethylpiperidine-1-oxyl) at C-6 of the polysaccharide gave products with 3.0, 5.1 and 9.5% of carboxyl groups as determined colorimetrically. Molecular mass analyses showed a decrease in the M-w of the oxidized galactoxyloglucans and an increase in angular fit from the RMS ratio versus molar mass plot. This indicated that the oxidation process generated a more rigid structure, going from a random coil in the native polymer to a rod conformation in the oxidized samples, probably due to the polyanionic structure. Thermogravimetric kinetics of degradation was obtained using the Arrhenius equation and an increase in the degradation rate, was apparently directly dependent on the oxidation level. (C) 2003 Elsevier B.V. All rights reserved.