Effect of Activity Coefficient of Polyvalent Ionic Salt Solution on Demulsification of Soy Lecithin Based Oil-in-Water Emulsion

Abstract

Lecithin based Oil-in-Water (O/W) emulsion finds a lot of applications in food and cosmetic industries. The stability of O/W emulsion depends on properties of the emulsifying solution and the ionic impurities present. The present experiment well explained the role of polyvalent Lewis acid salt solution in establishing the stability of emulsion. Lewis acid salts solutions of NaCl, KNO3 BaCl2 MgCl2, Al2(SO4)3 and FeCl3 were used in the preparation of lecithin based O/W emulsion. The ionic activity coefficient calculated from Debye-Hückel limiting law (DHLL) for Lewis metal ions Na+, K+, Ba2+, Mg2+, Al3+ and Fe3+ were found to be 0.955, 0.965,0.869,0.872, 0.737 and 0.737 which directly decrease the pH value of the ionic solutions to 6.9,7.0,7.14,7.04, 2.2 and 2.5 respectively. The conductance of ionic solution increases with decrease in ionic activity coefficient. These trends very strongly destabilize the lecithin O/W emulsion showing a significant order of breakup time of different emulsion systems as 3.5, 2.0,1.4,1.0, 0.5 and 0.25 minutes. The effect of ionic activity coefficient on emulsion destabilization was well projected by microscopic view. Measurement of droplet diameter was conspicuous for monovalent and divalent metal ions ranging from 14-156 micrometer and number of larger droplets increases with increasing in the valence. However, the higher valence Al3+ and Fe3+ ionic solutions totally break the emulsion with immediate separation of oil and water layer having lower activity coefficients. Thus, the increased valence and conductance, decreased ionic activity coefficient and pH value of the emulsifying solution destabilize the soy lecithin based O/W emulsion significantly by increasing the interfacial tension and retarding the binding ability of the emulsifier.