Disruption of Viscoelastic β-Lactoglobulin Surface Layers at the Air−Water Interface by Nonionic Polymeric Surfactants

• Published in: Langmuir 2004-11, Vol.20 (23), p.10150-10158
• Main Authors: Rippner Blomqvist, B, Ridout, M. J, Mackie, A. R, Wärnheim, T, Claesson, P. M, Wilde, P
• Format: Article
• Language: English
• Subjects: aba triblock copolymers; Adsorption; air/water interface; Animals; block-copolymer; Cattle; Chemistry; competitive adsorption; dilatational rheology; Elasticity; Fluorescence Recovery After Photobleaching; foam films; Fysikalisk kemi; In Vitro Techniques; Kemi; Lactoglobulins - chemistry; Membranes, Artificial; molecular-diffusion; NATURAL SCIENCES; NATURVETENSKAP; orogenic displacement; Physical chemistry; Polyethylenes - chemistry; Polypropylenes - chemistry; Rheology; sodium dodecyl-sulfate; Surface Properties; Surface-Active Agents - chemistry; thin liquid-films; Viscosity
• ISSN: 0743-7463; 1520-5827; 1520-5827
• DOI: 10.1021/la0485475

Nonequilibrium interfacial layers formed by competitive adsorption of β-lactoglobulin and the nonionic triblock copolymer PEO99−PPO65−PEO99 (F127) to the air−water interface were investigated in order to explain the influence of polymeric surfactants on protein film surface rheology and foam stability. Surface dilatational and shear rheological methods, surface tension measurements, dynamic thin-film measurements, diffusion measurements (from fluorescence recovery after photo bleaching), and determinations of foam stability were used as methods. The high surface viscoelasticity, both the shear and dilatational, of the protein films was significantly reduced by coadsorption of polymeric surfactant. The drainage rate of single thin films, in the presence of β-lactoglobulin, increased with the amount of added F127, but equilibrium F127 films were found to be thicker than β-lactoglobulin films, even at low concentration of the polymeric surfactant. It is concluded that the effect of the nonionic triblock copolymer on the interfacial rheology of β-lactoglobulin layers is similar to that of low molecular weight surfactants. They differ however in that F127 increases the thickness of thin liquid films. In addition, the significant destabilizing effect of low molecular weight surfactants on protein foams is not found in the investigated system. This is explained as due to long-range steric forces starting to stabilize the foam films at low concentrations of F127.