Extensional and shear rheology of okra hydrocolloid–saliva mixtures

Abstract

This is an investigation of the shear and extensional properties of okra polysaccharide–saliva mixtures, intended to model the mechanical behavior a food hydrocolloid during oral processing. Shear measurements show that incorporation of okra mucilage in saliva interferes with the self-assembly of salivary mucins, with partly detrimental effects on the low-shear viscosity of the mixture. This is counter-acted by excluded volume effects, as the overall concentration of macromolecules in the mixture reaches the semi-dilute regime. Particle tracking confirms the lack of direct interactions between the two polymeric populations. The contribution of extensional viscosity to the overall behavior of okra hydrocolloid–saliva mixtures is dominant, at about one to two orders of size higher than the equivalent shear values. The Trouton ratio values are in the order of tens or hundreds for the range of concentrations and deformation rates under study. Although the extensional viscosity dominates viscous flow, the two types of flow are equally important concerning the elastic behavior, giving insight on the mechanical behavior of mucilages in the oral cavity.