Comparative viscoelasticity studies: Corn fiber gum versus commercial polysaccharide emulsifiers in bulk and at air/liquid interfaces

Abstract

A comparative study of both the bulk and air/liquid interfacial rheological responses was carried out by using four kinds of representative high molecular weight and highly branched polysaccharide emulsifiers, (a) corn fiber gum (CFG), (b) octenyl succinate anhydride-modified starch (OSA-s), (c) gum arabic (GA) and (d) soybean soluble polysaccharides (SSPS), spanning the concentration range of 1–15 wt%. We found that the bulk and interfacial rheological properties of their aqueous solutions were significantly different. While both CFG and OSA-s showed Newtonian flow behavior at higher concentrations, both GA and SSPS exhibited obviously shear thinning behavior or thixotropy even at a low concentration of 1 wt%. The time-dependent flow behavior for CFG, GA and SSPS reflected microstructural breakdown and rebuilding in solutions under shear, indicated that their proteinaceous portion was strongly bound to their polysaccharide part. This phenomenon was not observed for the almost protein-free OSA-s. The interfacial rheology responses showed that the layers formed by CFG and OSA-s were viscously predominant with faster formation kinetics while they were elastically predominant for GA and SSPS with slower formation kinetics. Interfacial viscoelastic responses of CFG and OSA-s were weaker than those of GA and SSPS. By comparison, the interfacial layer for OSA-s showed pure viscous responses whereas SSPS showed the highest elastic responses. These significant disparities in bulk and interfacial viscoelasticity of the four polysaccharide emulsifiers reflect the influence of different fine chain structures on the dissimilarity in the intermolecular associations and the architectures of the interfacial layers.