The stability of guar gum in an aqueous system under acidic conditions

The stability of guar galactomannan in acidic conditions was investigated u sing dilute polymer solutions at temperatures of 25, 37 and 50 degrees C. T he depolymerisation of guar galactomannan was monitored by determining chan ges in solution viscosity, from which the viscosity-average molecular weigh t was estimated. The lowest pH values at which guar galactomannan remained stable were found to be 2.0, 3.0 and 3.5, respectively, at these temperatur es. The acid degradation appears to be a random scission process obeying fi rst order kinetics. The activation energy at pH 1.5, 2.0 and 3.0 were estim ated to be 117.4, 118.6 and 120.5 kJ mol(-1), respectively. This indicates that guar gum is reasonably stable under an acidic environment. The viscosi ty of fully hydrated guar gum solutions at acidic pH was found to be slight ly lower than it was at neutral pH even when no degradation occurred. Curre nt results suggest that guar gum maybe used in mild acidic processing condi tions, particularly when excessive heat treatment is not used. (C) 2000 Els evier Science Ltd. All rights reserved.