Rheological properties of oil-in water heat stable emulsions made from different stabilizers

Oil-in-water emulsions have attracted considerable attention in food industry due to their physical and rheological properties. These systems consist of small oil droplets dispersed in an aqueous medium. Numerous factors affect rheological properties of emulsions such as emulsion composition، process and storage conditions. In this study، effect of thermal treatment on oil in water emulsions 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 87ºC for 15 minutes. Rheological properties were studied using a Brookfield rotational viscometer. Thermal treatment had considerable influence on rheological properties of emulsions. Viscosity of all emulsions decreased after thermal treatment and stabilizers had a positive effect on this response. This behavior could be explained by the structural breakdown of the molecules due to the hydrodynamic forces generated and the increased alignment of the constituent molecules and hydrolization of stabilizers. All model emulsions exhibit non-newtonian pseudoplastic flow behavior often referred to as shear thinning (n<1). A non-linear relation between shear rate and shear stress can be observed. Shear stress versus shear rate data was successfully fitted to the Power-law model. Consistency coefficient (K) of emulsions decreased and flow behavior index (n) increased after thermal processing.