Mixed Layers of Sodium Caseinate + Dextran Sulfate: Influence of Order of Addition to Oil−Water Interface

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.

Colloidal interactions induced by overlap of mixed protein+polysaccharide interfacial layers

“…In fact the presence of substantial inter-diffusion in multi-layers, as well as lateral diffusion, has been reported by Yoo et al (2008). Other evidence for changes in the structure of multi-layers come from the work of Jourdain, Schmitt, Leser, Murray, & Dickinson (2009). In this study, interfacial adsorbed films were formed on n-tetradecane -water interfaces in two different ways, involving mixtures of sodium caseinate and dextran sulphate.…”

Mixed protein–polysaccharide interfacial layers: effect of polysaccharide charge distribution

“…This is about an order of magnitude smaller than experimental data obtained usingpotentials measurements. 29,30,53,61 This situation is altered dramatically for non-uniformly charged polysaccharides, as 45 evident from the data presented in Figs. 11b to 11d.…”

“…food emulsions). In a series of interesting experiments, Jourdain et al 53 compared the dynamic interfacial tension behaviour of the 25 mixed films of the protein, sodium caseinate, and the polysaccharide, dextran sulphate, adsorbed at n-tetradecane-water interfaces in two different ways. In the first of these, the adsorption took place in a single step from a mixed solution of these two biopolymers.…”

“…However, after around 20 35 minutes or so, the measured interfacial tensions were seen to approach the same value. 53 This is thought to be due to the evolution of the structure of the two films towards the same equilibrium configuration.…”

Influence of pH value and locust bean gum concentration on the stability of sodium caseinate-stabilized emulsions

“…If there is to be any adsorption of LBG this would have to be in the form of a secondary layer adsorbed on top of the primary caseinate layer. Adsorption of polysaccharides to hydrophobic-hydrophilic interfaces in this manner has been investigated both experimentally (Guzey & McClements, 2006;Guzey & McClements, 2007;Jourdain, Schmitt, Leser, Murray, & Dickinson, 2009) and through numerical theoretical calculations (Ettelaie, Akinshina, & Dickinson, 2008;Ettelaie, Akinshina, & Maurer, 2012). These studies have shown the need for strong favorable interactions between protein and polysaccharides before the formation of a secondary adsorbed layer by the latter can commence.…”