Comparison of methods of zeta potential and residual turbidity of pectin solutions using calcium sulphate/aluminium sulphate as a precipitant

Abstract

The affinity of calcium ion binding from CaO used in the most common process of purification of sugar beet juice is relatively low. Therefore, large amounts of this compound are required. This paper presents the theoretical basis of a novel sugar beet juice purification method based on the application of the binary system CaSO4/Al2(SO4) . In order to monitor the process of coagulation and precipitation of pectin in the presence of CaSO4/Al2(SO4)3, two methods were compared: measurement of the zeta potential and of residual solution turbidity. The zeta potential of pectin solution was determined by electrophoretic method, while the residual turbidity was determined by spectrophotometry. Two model solutions of pectin (0.1 % w/w) were investigated. Studies were performed with 10 different concentrations of the binary solution CaSO4/Al2(SO4)3 (50 - 500 g dm-3). The amount of the precipitant CaSO4/Al2(SO4)3 (1:1 w/w) needed to achieve the minimum solution turbidity and charge neutralization of pectin particles (zero zeta potential) were measured and compared. Colloidal destabilization occurred before a complete neutralization of the surface charge of pectin particles (zeta potential ~ 0 mV). Optimal quantities (490 - 705 mg g-1 pectin) of the applied binary mixture, were obtained using both methods. This is much lower than the amount of CaO that is commonly used in the conventional process of sugar beet juice purification (about 9 g? g-1 pectin). The use of these precipitants could be important from both economic and environmental point of view.