Studying the Role of Xanthan Gum upon the Rheology and Stability of Oil/Water Emulsions

Abstract

The applications of emulsions are numerous. Many products of commercial importance are sold in emulsion form. The industries where emulsions are of considerable importance include petroleum, food, medical and pharmaceutical, cosmetics, agriculture, explosives, polishes, leather, textile, bitumen, paints, lubricants, polymer, and transport, among others. Particularly, food emulsions exhibit a great diversity of rheological characteristics, ranging from low-viscosity Newtonian liquids (e.g. milk, fruit beverages), to viscoelastic materials (e.g. salad dressings) and to plastic materials (e.g. butter). This diversity is the result of the different sorts of ingredients and processing conditions used to create each unique type of product. Polysaccharides are usually added to the aqueous phase of low-in-fat o/w food emulsions to improve their creaming stability. Their efficiency depends on polymer concentration in the aqueous phase as well as on the structural features of the aqueous polymer system.Xanthan gum is one of the hydrocolloids most used as emulsion stabilizer because of its unique rheological behavior. It forms highly viscous shear thinning solutions at very low concentrations and the viscosity is not influenced to any great extent by changes in pH, the presence of salts and temperature. The high viscosity at low shear enables the gum to prevent particle sedimentation and droplet creaming and the shear thinning characteristics ensure that the product readily flows from the bottle after shaking.The present chapter is oriented to interpret and model the rheological behavior of oil-in-water emulsions stabilized singly with xanthan gum or combined with different hydrocolloids, like guar gum or potato starch. The effect of hydrocolloids concentration was studied using oscillatory measurements within the linear viscoelastic range. Viscoelastic behavior of the systems was satisfactorily modeled using generalized Maxwell equation. This empirical model was used to predict the mechanical relaxation spectrum for both emulsions and continuous aqueous phases. Flow properties were determined through rotational experiments and changes during storage time were analyzed using parameters of the Cross model on the flow curves.Droplet size distribution was measured by image analysis. Microscopic observations revealed that emulsions containing xanthan gum did not significantly change the average droplet diameter during the first month of storage. Visual inspections of the formulated emulsions showed that they remained stable after six months even emulsions with low oil content (10%).