(33i) Polysaccharides As Food Thickeners

Foods are multicomponent soft materials that often contain dispersed drops, bubbles, particles, or proteins. Often protein-based foams, emulsions, suspensions, and pastes contain polysaccharides that act as binders, thickeners, gelling agents or rheology modifiers, and influence shelf-life, rheology, processability as well as control over fiber, fat, salt, calorie count, texture, and mouth-feel. Stream-wise velocity gradients associated with extensional flows spontaneously arise during extrusion, calendaring, coating, dispensing, bubble growth or collapse as well as consumption including swallowing and suction via straws. Even though shear rheology response is fairly well characterized and utilized in food industry, elucidating, measuring and harnessing the extensional rheology response have remained longstanding challenges. The characterization challenges include the lack of robust, reliable and affordable methods for measuring extensional rheology response, whereas the product design challenges stem from the difficulties in assessing or predicting the influence of macromolecular properties on macroscopic rheological behavior. In this contribution, we address the characterization challenges for specific case of xanthan gum and cellulose gum thickeners by using dripping-onto-substrate (DoS) rheometry protocols that we developed that rely on analysis of capillary-driven thinning and break-up of liquid necks created by releasing a finite volume of fluid onto a substrate. The DoS rheometry protocols emulate the heuristic tests of thickening, stickiness or cohesiveness based on dripping a sauce from a ladle or dispensing from a nozzle onto a substrate. We investigate the concentration-dependent variation in shear and extensional rheology of polysaccharide thickeners. We show that adding glycerol or changing salt concentration can be used for tuning the pinch-off dynamics, extensional rheology response, and processability of unentangled solutions of cellulose gum, whereas entangled solutions are relatively insensitive to change in salt concentration.