ABSTRACT
Rheology is the science concerned with the deformation and ow of matter (Tadros 2010, Rao 2013, van Vliet 2013). Most rheological tests involve applying a specic force to a material and measuring the resulting ow and/or deformation of the material. The rheological properties of a material are then established by analyzing the relationship between the applied force and the resultant ow or deformation. Knowledge of the rheological properties of food emulsions is important for a variety of reasons (Chen and Stokes 2012, Selway and Stokes 2014). The efciency of droplet disruption in a homogenizer depends on the viscosity of the individual components, as well as on the overall rheology of the product (Chapter 6). The shelf life of many food emulsions depends on the rheological characteristics of the component phases, for example, the creaming of oil droplets in oil-in-water emulsions is strongly dependent on the viscosity of the aqueous phase (Chapter 7). Information about the rheology of food emulsions is used by food engineers to design processing operations that depend on the way that the product ows, for example, ow through a pipe, stirring in a mixer, passage through a heat exchanger, packaging into containers (Singh and Heldman 2013). Many of the sensory attributes of food emulsions are directly related to their rheological properties, for example, creaminess, thickness, smoothness, spreadability, pourability, owability, brittleness, and hardness (Chapter 9). A food manufacturer must therefore be able to design and consistently produce a product that has the desirable rheological properties expected by the consumer. Finally, rheological measurements are frequently used by food scientists as an analytical tool to provide fundamental insights about the structural organization and interactions of the components within emulsions, for example, measurements of viscosity versus shear rate can be used to provide information about the strength of the colloidal interactions between droplets (Quemada and Berli 2002, Tadros 2010). The purpose of this chapter is to present the general principles of rheology, to discuss the relationship between the rheological characteristics of food emulsions and their colloidal properties, and to provide an overview of analytical instruments used to characterize the rheological properties of food emulsions.
