Effect of several electrolytes on the rheopectic behaviour of concentrated soy lecithin dispersions

Concentrated dispersions of soy lecithin (60 g/L) prepared by sonication-freezing-unfreezing method show a non-newtonian behaviour and a significant rheopexy. Shear stress versus shear rate plots shows a loop hysteresis area, which have been studied in soy lecithin dispersions prepared with aqueous solutions of various electrolytes (NaCl, CaCl2, MgCl2 and AlCl3) with concentrations in the range 10(-5) to 10(-2) mol/L. Also we have studied the effect of different pH on soy lecithin dispersions. The results have revealed a very sensitive influence of nature, valence and concentration of the respective cations and the pH value on the loop hysteresis area values. It seems to indicate that the vesicle formation by segregation process followed by vesicle fusions is involved in the rheopectic effect. (c) 2005 Elsevier B.V. All rights reserved.