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

The stability of guar galactomannan in acidic conditions was investigated using dilute polymer solutions at temperatures of 25, 37 and 50°C. The depolymerisation of guar galactomannan was monitored by determining changes in solution viscosity, from which the viscosity-average molecular weight 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 temperatures. The acid degradation appears to be a random scission process obeying first order kinetics. The activation energy at pH 1.5, 2.0 and 3.0 were estimated 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 viscosity of fully hydrated guar gum solutions at acidic pH was found to be slightly lower than it was at neutral pH even when no degradation occurred. Current results suggest that guar gum may be used in mild acidic processing conditions, particularly when excessive heat treatment is not used.