Structural and physicochemical changes in guar gum by alcohol-acid treatment

The aim of this study was to evaluate the effects of alcohol-acid degradation on the structural and physicochemical characteristics of guar gum. Guar gum (50 wt.%) was treated with methanol, ethanol, 2-propanol, or 1-butanol containing 1 or 2 mL 36% hydrochloric acid at 75 degrees C for 30-240 min. The linear relationship between 1/Mw and time suggested that alcohol-acid degradation followed first-order kinetics with rate constants varying directly with the number of alcohol carbon atoms and acid concentration. Alcohol-acid treatment exerted no effect on the chemical and crystal structure of guar but significantly decreased shear viscosity, slightly increased solubility, mildly reduced thermostability, and dramatically darkened colour. This study extended the knowledge of the effect of alcohol on the acid hydrolysis of guar and will contribute to the development of a large-scale procedure for guar gum degradation.