CaO&CaSO4 and CaO&Al2(SO4)3 as Pectin Precipitants–Model of Overlapping Diffuse Layers

Abstract

This work is concerned with the theoretical basis of novel sugar beet juice purification method using binary systems CaO&CaSO₄ and CaO&Al₂(SO₄)₃. The Gouy–Chapman–Stern (GCS) model of overlapping of diffuse layers of EDLs on pectin surface and that on Ca²⁺ and Al³⁺ ions, theoretically explains this method. The change of the zeta potential was used to quantitatively indicate overlapping of diffuse layers. For the experiment two model solutions of pectin (0.1 % w/w) were prepared, while the concentrations of CaO&CaSO₄ and CaO&Al₂(SO₄)₃ in the range of 50–500 g dm^-3 were used. The greater decrease in the absolute value of zeta potential indicated greater overlapping of diffuse layers between pectin particles and Ca²⁺ and Al³⁺ ions and faster coagulation of pectin. The overlapping degree increased with increased concentration of these binary systems. Pectin with a greater surface charge and multivalent Al³⁺ from CaO&Al₂(SO₄), exerted a greater impact on the zeta potential. Optimal quantities of the applied binary mixtures were as follows: 256–640 mg g^-1 pectin. This is much lower than CaO commonly used in the conventional process of sugar beet juice purification (about 9 g g^-1 pectin).