title: Effect of the interfacial layer composition on the properties of emulsion creams.
abstract: We have quantified observed differences in the microstructure and rheology of creaming emulsions stabilized by protein and low molecular weight surfactants. In this study, we made two sets of emulsions from a single parent emulsion, which differed only in their interfacial composition (i.e., either protein or surfactant). The protein studied was whey protein isolate. The zeta potential of the surfactant-stabilized emulsion was controlled by mixing anionic (SDS) and nonionic (Brij 35) surfactants to match the zeta potential of the protein-stabilized emulsion. Despite this, ultrasonic creaming measurements and confocal microscopy showed that the structures within the cream layers were different between the two sets of emulsions. The protein-stabilized emulsions appeared to slow or arrest the packing within the cream, leading to a lower density network of emulsion droplets, whereas the surfactant emulsion droplets rearranged more quickly into a well-packed, concentrated cream layer. Rheological analysis of the creams showed that despite the protein-stabilized emulsions having a lower dispersed phase volume fraction, their elastic modulus was approximately 30 times greater than that of a comparable surfactant-stabilized emulsion. These differences were caused by the ability of the protein to form a highly viscoelastic interfacial network around the droplets which may include intermolecular covalent cross-links. At close range the adhesive nature of the interaction between the layers contributes to the microstructure and rheology of concentrated emulsions. This is the first time that such well-defined emulsion systems have been studied in detail both noninvasively to look at the impact on creaming and also invasively to look at the impact on bulk rheological properties.
authors.affiliation: Structuring Food for Health Programme, Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, United Kingdom. alan.mackie@bbsrc.ac.uk
authors.forename: Alan R
authors.initials: AR
authors.lastname: Mackie
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ridout
authors.forename: Graham
authors.initials: G
authors.lastname: Moates
authors.forename: Fiona A
authors.initials: FA
authors.lastname: Husband
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Wilde
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004655:Emulsions / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry; D011506:Proteins / Q000737:chemistry; D012212:Rheology; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry
chemical_list: D004655:Emulsions; D011506:Proteins; D013501:Surface-Active Agents; D012967:Sodium Dodecyl Sulfate; D011092:Polyethylene Glycols; C515901:Brij 35