1Academic Member of the Department of Food Science and Technology, Shahrekord Branch, Islamic Azad University, Shahrekord, Iran.
2Assistant Professor of the Department of Food Science and Technology, College of Agriculture, Isfahan University of Technology, Isfahan, Iran.
3Assistant Professor of the Department of Food Science and Technology, Shahrekord Branch, Islamic Azad University, Shahrekord, Iran.
Oil in water emulsions have attracted considerable attention in food industry due to their large applications. In this study, the effect of thermal treatment on oil in water emulsions (o/w) containing 40% oil was studied. The emulsions were prepared using xanthan gum, guar gum and carboxymethyl cellulose as stabilizer and polyoxyethylen sorbitan monooleat as emulsifier. A mixture design was used to define the percentage of each stabilizer to simulate wide range of emulsions. The emulsions were pasteurized at 87 ºC for 15 minutes. Thermal treatment had a considerable influence on rheological properties of the emulsions. Viscosity of all emulsions decreased after thermal treatment and stabilizers had increasing effect on this response. All emulsionsexhibited non Newtonianpseudo plastic flow behaviorthat often referred to as shear thinning (n<1). A non linear relation between shear rate and shear stress was observed. Shear stress versus shear rate data was successfully fitted to the Power-law model. Consistency coefficient (K) decreased and flow behavior index (n) increased after thermal processing. Thermal treatment caused an increase in particle size of emulsions because of coalescence. Some of emulsions had heterogeneous coalescence (bimodal) and some of them had homogenous coalescence (mono modal). All emulsions were stable to centrifugation and did not breakdown. It was found that surface tension was affected more by temperature than by stabilizer content. Surface tension decreased by thermal processing. Viscosity of all the samples was reduced during storage. The results showed that developed emulsions are thermally under pasteurization temperatures.