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Journal Article

Specific effects of Ca2+ ions and molecular structures of β-lactoglobulin interfacial layers that drive macroscopic foam stability

MPS-Authors
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Gochev,  Georgi
Reinhard Miller, Biomaterialien, Max Planck Institute of Colloids and Interfaces, Max Planck Society;

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Miller,  Reinhard
Reinhard Miller, Biomaterialien, Max Planck Institute of Colloids and Interfaces, Max Planck Society;

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2306223.pdf
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2306223_supp.pdf
(Supplementary material), 2MB

Citation

Braunschweig, B., Schulze-Zachau, F., Nagel, E., Engelhardt, K., Stoyanov, S., Gochev, G., et al. (2016). Specific effects of Ca2+ ions and molecular structures of β-lactoglobulin interfacial layers that drive macroscopic foam stability. Soft Matter, 12(27), 5995-6004. doi:10.1039/C6SM00636A.


Cite as: http://hdl.handle.net/11858/00-001M-0000-002A-E95F-5
Abstract
β-lactoglobulin (BLG) adsorption layers at air-water interfaces were studied in situ with vibrational sum-frequency generation (SFG), tensiometry, surface dilatational rheology and ellipsometry as a function of bulk Ca2+ concentration. The relation between the interfacial molecular structure of adsorbed BLG and the interactions with the supporting electrolyte is additionally addressed on higher length scales along the foam hierarchy – from the ubiquitous air-water interface through thin foam films to macroscopic foam. For concentrations <1 mM, a strong decrease in SFG intensity from O-H stretching bands and a slight increase in layer thickness and surface pressure are observed. A further increase in Ca2+ concentrations above 1 mM causes an apparent change in the polarity of aromatic C-H stretching vibrations from interfacial BLG which we associate to a charge reversal at the interface. Foam film measurements show formation of common black films at Ca2+ concentrations above 1 mM due to considerable decrease of the stabilizing electrostatic disjoining pressure. These observations also correlate with a minimum in macroscopic foam stability. For concentrations >30 mM Ca2+, micrographs of foam films show clear signatures of aggregates which tend to increase the stability of foam films. Here, the interfacial layers have a higher surface dilatational elasticity. In fact, macroscopic foams formed from BLG dilutions with high Ca2+ concentrations where aggregates and interfacial layers with higher elasticity are found, showed the highest stability with much smaller bubble sizes.