Capillary breakup and extensional rheology response of food thickener cellulose gum (NaCMC) in salt-free and excess salt solutions

Abstract

Cellulose gum, also known as sodium carboxymethyl cellulose (NaCMC), is a polysaccharide often used as a thickener or rheology modifier in many industrial complex fluids, including foods. Shear and extensional rheology response influence production and processing of food, as well as the consumer perception and bioprocessing that begin with every bite. Stream-wise velocity gradients associated with extensional flows spontaneously arise during extrusion, calendaring, coating, dispensing, bubble growth or collapse, as well as during consumption including swallowing and suction via straws. The influence of polysaccharides on shear rheology response is fairly well characterized and utilized in food industry. In contrast, elucidating, measuring, and harnessing the extensional rheology response have remained longstanding challenges and motivate this study. The characterization challenges include the lack of robust, reliable, and affordable methods for measuring extensional rheology response. 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 using dripping-onto-substrate (DoS) rheometry protocols that rely on analysis of capillary-driven thinning and breakup 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. 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 changes in salt concentration.