Zeta potentials of gum arabic stabilised oil in water emulsions

The electrostatic contribution to the mechanism by which gum arabic stabili ses oil in water has been investigated using laser Doppler electrophoresis. Electrophoretic mobilities of D-limonene emulsion droplets measured in 10( -3), 10(-2) and 10(-1) M NaCl over a pH range from 1 to 10, and 10(-3)-10(- 1) M CaCl2 in doubly distilled water, yielded relatively low potentials (le ss than 28 mV in magnitude). The interpreted zeta potentials are less than those required for electrostatic stabilisation alone. This data supports th e postulated steric stabilisation mechanism with a finite electrostatic con tribution. A model which suggests the arabino galacto proteins are adsorbed -via the proteins-to the interface with the polysaccharide moieties protrud ing into solution to give rise to a steric stabilising layer is supported b y the data. No charge reversal is observed for the Ca solutions in contrast to the pH data indicating that some of the charge groups are inaccessible to the Ca ions. (C) 1999 Elsevier Science Ltd. All rights reserved.