title: αs-Casein-PE6400 mixtures: surface properties, miscibility and self-assembly.
abstract: Surface properties, miscibility and self-assembly of mixtures of a food-grade αs-casein and the triblock copolymer PE6400 (PEO13-PPO30-PEO13) were examined. The properties at the surface were determined by surface pressure measurements for a 1:1 molar mixture. Comparison of the measured with the calculated isotherms show attractive interactions at surface pressures above 9mN/m. The miscibility gaps of solutions containing 0.004-0.2mmol/l αs-casein and 0.02-0.1mol/l polymer were examined. It was found that a one-phase region exists at distinct mixing ratios and temperatures. Comparison of the cloud points of mixtures of αs-casein and PE6400 with pure αs-casein showed that the presence of the triblock copolymer enhanced the solubility of the protein. The ζ-potential of the αs-casein solution decreased by addition of PE6400 to zero. Our results thus suggest that αs-casein and PE6400 are miscible. The results of the cloud point and ζ-potential measurements were explained by formation of a mixed aggregate where the PPO chains are anchored inside the hydrophobic part of the αs-casein while the PEO chains cover the charged hydrophilic part of the αs-casein thereby leading to an increase of the cloud point and a decrease in ζ-potential. This is in agreement with the attractive interactions between αs-casein and PE6400 as observed via surface pressure measurements at the surface.
authors.affiliation: Department of Food Physics and Meat Science, Institute of Food Science and Biotechnology, University of Hohenheim, Garbenstraße 21/25, 70599 Stuttgart, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Kessler
authors.affiliation: Department of Dairy Science and Technology, Institute of Food Science and Biotechnology, University of Hohenheim, Garbenstraße 25, 70599 Stuttgart, Germany.
authors.forename: Orquidéa
authors.initials: O
authors.lastname: Menéndez-Aguirre
authors.affiliation: Department of Dairy Science and Technology, Institute of Food Science and Biotechnology, University of Hohenheim, Garbenstraße 25, 70599 Stuttgart, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Hinrichs
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
authors.forename: Cosima
authors.initials: C
authors.lastname: Stubenrauch
authors.affiliation: Department of Food Physics and Meat Science, Institute of Food Science and Biotechnology, University of Hohenheim, Garbenstraße 21/25, 70599 Stuttgart, Germany. Electronic address: j.weiss@uni-hohenheim.de.
authors.forename: Jochen
authors.initials: J
authors.lastname: Weiss
mesh_terms: D002364:Caseins / Q000737:chemistry*; D004548:Elasticity; D011092:Polyethylene Glycols / Q000737:chemistry*; D011312:Pressure; D012995:Solubility; D012996:Solutions; D055672:Static Electricity; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry
chemical_list: D002364:Caseins; D012996:Solutions; D013501:Surface-Active Agents; C472329:poly(ethyleneoxide)(13)-poly(propyleneoxide)(30)-poly(ethyleneoxide)(13) block copolymer; D011092:Polyethylene Glycols
keywords: Miscibility gap; Mixed micelle; PEO(13)–PPO(30)–PEO(13); Surface properties; α(s)-Casein; ζ-Potential