title: Interfacial rheology of surface-active biopolymers: Acacia senegal gum versus hydrophobically modified starch.
abstract: Acacia gum is a hybrid polyelectrolyte containing both protein and polysaccharide subunits. We study the interfacial rheology of its adsorption layers at the oil/water interface and compare it with adsorbed layers of hydrophobically modified starch, which for economic and political reasons is often used as a substitute for Acacia gum in technological applications. Both the shear and the dilatational rheological responses of the interfaces are considered. In dilatational experiments, the viscoelastic response of the starch derivative is just slightly weaker than that for Acacia gum, whereas we found pronounced differences in shear flow: The interfaces covered with the plant gum flow like a rigid, solidlike material with large storage moduli and a linear viscoelastic regime limited to small shear deformations, above which we observe apparent yielding behavior. In contrast, the films formed by hydrophobically modified starch are predominantly viscous, and the shear moduli are only weakly dependent on the deformation. Concerning their most important technological use as emulsion stabilizers, the dynamic interfacial responses imply not only distinct interfacial dynamics but also different stabilizing mechanisms for these two biopolymers.
authors.affiliation: Institute of Food Science and Nutrition and Materials Research Center, ETH Zürich, 7 Rue de la Bergère, Zürich, Switzerland. erni@mit.edu
authors.forename: Philipp
authors.initials: P
authors.lastname: Erni
authors.forename: Erich J
authors.initials: EJ
authors.lastname: Windhab
authors.forename: Rok
authors.initials: R
authors.lastname: Gunde
authors.forename: Muriel
authors.initials: M
authors.lastname: Graber
authors.forename: Bruno
authors.initials: B
authors.lastname: Pfister
authors.forename: Alan
authors.initials: A
authors.lastname: Parker
authors.forename: Peter
authors.initials: P
authors.lastname: Fischer
mesh_terms: D006170:Gum Arabic / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D012212:Rheology; D013053:Spectrophotometry; D013213:Starch / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D013501:Surface-Active Agents; D006170:Gum Arabic; D013213:Starch