Rheo-NMR: Applications to food

Typical consumer products such as ketchup, mayonnaise, hair gel, and coffee powder display a combination of solid-like and fluid-like properties. The shear flow behavior of these materials is usually examined with a rheometer, which in the simplest case provides a fluid viscosity as a function of the applied shear stress or strain rate. Traditional rheometry, however, does not provide information about the microscopic phenomena that underlie the apparent bulk flow behavior. Rheo- NMR, a combination between rheology and nuclear magnetic resonance (NMR) methodology, allows measurement and characterization of microscopic phenomena in the gap of shear geometries such as the Couette or cone-plate. Most notably, it provides access to the fluid velocity profile across the shear gap, the shape of which contains information about yield stress, shear thinning and thickening properties of the fluid, and flow heterogeneities. This chapter explores the basic concepts of rheology and rheo-NMR and illustrates the use of rheo- NMR to gain insight in the flow of food systems in two brief case studies.