Thixotropic Behavior of Salad Dressings Stabilized with Modified Starch, Pectin, and Gellan Gum. Influence of Temperature

The thixotropy of low‐oil salad dressing has been analyzed at different temperatures (8–26°C). The usual formulation containing modified starch (4%) was compared with others in which part of the starch had been substituted by pectin (0.5%) or different concentrations of gellan (0.1 and 0.5%). Up and down flow curves were measured, showing in all cases shear thinning behavior and fitting the Herschel‐Bulkley model. Thixotropic areas enclosed by the up curve and the corresponding different down curves, S_Th, were obtained. With the aim of establishing comparative results, and since the viscosities were quite different, the parameter considered was relative thixotropic area, S_R (%)=100 (S_Th/S_up). These areas increased with agitation time and depended on temperature. Their tendencies were reproduced by equations S_R=S_Rmax {1‐exp [‐f(t)]}, with f(t)=βt^0.5, where the maximum relative thixotropic area, S_Rmax , increases with increasing temperature while β decreases. The parameter β has different values for each formulation, and indicates the time dependence. The emulsion formulated with pectin was found to be the most stable with temperature and agitation time, while the greatest thixotropy corresponded to the emulsion formulated with starch only. The thixotropic behavior of the emulsions formulated with gellan gum was seen to be intermediate between the two above formulations—the emulsion formulated with the largest percentage of gellan gum being the least thixotropic of both.

Keywords:

• Thixotropic behavior
• gellan gum
• emulsion
• hydrocolloids