Rheological study of galactomannan depolymerisation at elevated temperatures: Effect of varying pH and addition of antioxidants

Guar gum (GG) and locust bean gum (LBG) are neutral and should not be expected to change viscosity at different pH values. However, heat treatment at 100 °C within the range of pH values 5.0–9.0 did show significant differences in viscosity. Lowest viscosity and therefore probable maximum degradation was found at pH 7.0 which is indicative of free radical attack being optimum at this pH. idants, sodium sulphite (SS) and propyl gallate (PG), added at 1000 and 500 ppm, respectively, provide both gums with stability when subjected to temperature treatments up to 121 °C. This also supports the proposal that it is the action of free radicals at higher temperatures that causes thermal degradation. LBG shows a better conservation of viscosity than GG, on addition of antioxidants, suggesting that the protective effect of its intermolecular associations is further enhanced by the antioxidants.