EFFECT OF SALTS ON INTERACTIONS OF STARCH WITH GUAR GUM

The cold paste viscosity and the gelatinization temperature of starch, when used alone and in combination with guar was found to be sensitiv e to the presence of salts at concentrations normally encountered in f ood systems. It is thought that gums facilitate the formation of an el ectrical double layer of cations around the starch and hence and delay the gelatinization temperature. Since the starch exchanges cations fr om the hydrogen ions in the presence of salts, an increase in volume, results, causing an increased cold paste viscosity of starch-salt syst ems. However, in the starch-guar gum system, different salts show diff erent behaviours. While calcium chloride and potassium chloride showed an increase in cold paste viscosity, sodium sulphate and sodium phosp hate showed a decrease. Sodium chloride on the other hand showed a beh aviour dependent on the concentration of guar gum. While no significan t effect of sodium chloride on the cold paste viscosity was observed a t 0.05 and 0.1% guar, the viscosity was found to decrease with increas ing sodium chloride concentration in the presence of 0.2% guar. These results generally were in line with the rheological profile, as seen f rom the values of the consistency index. The addition of salts to star ch alone as well as starch-guar combinations caused a decrease in flow behaviour index, suggesting that both guar and salts make the starch pastes more pseudoplastic. These results would be valuable in developi ng starch-based thickeners for food products containing salts.