Research article summary (published 30 Aug 2009):

Mixed layers of sodium caseinate + dextran sulfate: influence of order of addition to oil-water interface.

Full Abstract

We report on the interfacial properties of electrostatic complexes of protein (sodium caseinate) with a highly sulfated polysaccharide (dextran sulfate). Two routes were investigated for preparation of adsorbed layers at the n-tetradecane-water interface at pH = 6. Bilayers were made by the layer-by-layer deposition technique whereby polysaccharide was added to a previously established protein-stabilized interface. Mixed layers were made by the conventional one-step method in which soluble protein-polysaccharide complexes were adsorbed directly at the interface. Protein + polysaccharide systems gave a slower decay of interfacial tension and stronger dilatational viscoelastic properties than the protein alone, but there was no significant difference in dilatational properties between mixed layers and bilayers. Conversely, shear rheology experiments exhibited significant differences between the two kinds of interfacial layers, with the mixed system giving much stronger interfacial films than the bilayer system, i.e., shear viscosities and moduli at least an order of magnitude higher. The film shear viscoelasticity was further enhanced by acidification of the biopolymer mixture to pH = 2 prior to interface formation. Taken together, these measurements provide insight into the origin of previously reported differences in stability properties of oil-in-water emulsions made by the bilayer and mixed layer approaches. Addition of a proteolytic enzyme (trypsin) to both types of interfaces led to a significant increase in the elastic modulus of the film, suggesting that the enzyme was adsorbed at the interface via complexation with dextran sulfate. Overall, this study has confirmed the potential of shear rheology as a highly sensitive probe of associative electrostatic interactions and interfacial structure in mixed biopolymer layers.

Author information

Author/s: Jourdain, Laureline S (LS); Schmitt, Christophe (C); Leser, Martin E (ME); Murray, Brent S (BS); Dickinson, Eric (E);

Affiliation: Food Science and Technology Department, Nestle Research Center, CH-1000 Lausanne 26, Switzerland.

Grants: (Agency:Biotechnology and Biological Sciences Research Council)

Journal and publication information

Publication Type: Journal Article; Research Support, Non-U.S. Gov't

Journal: Langmuir : the ACS journal of surfaces and colloids (Langmuir), published in United States. (Language: eng)

Reference: 2009-Sep; vol 25 (issue 17) : pp 10026-37

Dates: Created 2009/08/26; Completed 2009/11/03;

PMID: 19459686, status: MEDLINE (last retrieval date: 11/3/2009, IMS Date: )

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Adsorption Caseins - chemistry Dextran Sulfate - chemistry Enzymes - chemistry Hydrogen-Ion Concentration Lipid Bilayers - chemistry Microscopy, Confocal - methods Oils - chemistry

Oils - chemistry Polysaccharides - chemistry Proteins - chemistry Rheology - methods Static Electricity Stress, Mechanical Surface Properties Water - chemistry

Associated Chemicals: Caseins (0) ; Enzymes (0) ; Lipid Bilayers (0) ; Oils (0) ; Polysaccharides (0) ; Proteins (0) ; Water (7732-18-5) ; Dextran Sulfate (9042-14-2)

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