Guidelines for processing emulsion-based foods

Abstract

Emulsions are dispersions of one liquid into the second immiscible liquid in the form of fine droplets. Emulsions can be classified as either oil-in-water or water-inoil emulsions depending on whether oil or water is the dispersed phase. Milk, cream and sauces are some examples of oil-in-water emulsions whereas butter and margarine are examples of water-in-oil emulsions. Ice cream and fabricated meat products are complex oil-in-water emulsions in which either additional solid particles are present or the continuous phase is semi-solid or a gel. Some examples of emulsions is shown in Table 13.1. Formation of emulsion results in a large interfacial area between two immiscible phases and therefore is usually associated with an increase in free energy. Consequently, emulsions are thermodynamically unstable, i.e., they will phase separate eventually. However, emulsifiers and proteins are usually employed in the formulation. They adsorb at the liquid-liquid interface thus lowering the interfacial tension. Smaller interfacial tension helps in the dispersion of one phase in the form of fine droplets by lowering the required interfacial energy. In addition, the emulsifiers and proteins also modify the interdroplet forces thereby either preventing or retarding the rate of coalescence of colliding droplets during emulsion formation. Formulation therefore influences the size of emulsion drops formed using different types of emulsification equipment. Modification of interdroplet forces also helps in prolonging shelf life (kinetic stability) by slowing the rate of coarsening of emulsion drop size due to coalescence during storage. Proteins and emulsifiers also help in the extension of shelf life by providing rheological properties to the liquid-liquid interface. The main focus of this chapter is formation of emulsion. The chapter attempts to highlight the salient features of formation of emulsions and a brief description of different factors that control the drop size. Different types of emulsification equipment, the nature of flow field, breakup and coalescence of droplets and prediction of drop size during emulsion formation are discussed. No attempt has been made to discuss the mechanisms of destabilization of emulsion products during storage. Comprehensive treatments of this subject can be found elsewhere (Narsimhan, 1992; Robins and Hibberd, 1998; McClements, 1999; Becher, 2001). © 2008 Springer New York.