Foams and emulsions. Disproportionation kinetics of air bubbles stabilized by food proteins andnanoparticles

Dickinson, Eric; Murray, Brent S.; Du, Zhiping; Ettelaie, Rammile; Kostakis, Thomas; Vallet, Julien

doi:10.1039/9781847552389-00257

Cited by 1 publication

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“…We postulate that these were protein aggregates. Such features have been observed previously with commercial whey protein, and OA is especially known to readily coagulate at interfaces . The isoelectric pH of OA is 4.8 25 and hydrophobic interactions are more predominant at a pH value closer to the isoelectric point (pI) of the protein .…”

Section: Resultssupporting

confidence: 72%

“…There is some overall slow drift of sections of the interface, which agrees with the observed rotation of the banded domains, indicating that there is some capacity for more rearrangement of sections of the interface. Thus, initially at least, it seems reasonable to assume that the latex particles become embedded in the protein film as it builds up around them and that they remain essentially trapped in their relative local positions by the highly viscoelastic, gel-like film that β-L forms on adsorption under such conditions …”

Section: Resultsmentioning

confidence: 99%

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Morphological Changes in Adsorbed Protein Films at the Air−Water Interface Subjected to Large Area Variations, as Observed by Brewster Angle Microscopy

Dickinson

Murray

2007

Langmuir

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Adsorbed films of proteins at the air-water interface have been imaged using Brewster angle microscopy (BAM). The proteins beta-lactoglobulin (beta-L) and ovalbumin (OA) were studied at a range of protein concentrations and surface ages at 25.0 degrees C and two pH values (7 and 5) in a Langmuir trough. The adsorbed films were periodically subjected to compression and expansion cycles such that the film area was typically varied between 125% and 50% of the original film area. With beta-L on its own, no structural changes were observable at pH 7. When a low-area fraction (less than 0.01%) of 20 mum polystyrene latex particles was spread at the interface before adsorption of beta-L, the particles became randomly distributed throughout the interface, but after protein adsorption and compression/expansion, the particles highlighted notable structural features not visible in their absence. Such features included the appearance of long (several hundred micrometers or more) folds and cracks in the films, generally oriented at right angles to the direction of compression, and also aggregates of protein and/or particles. Such structuring was more visible the longer the film was aged or at higher initial protein concentrations for shorter adsorption times. At pH 5, close to the isoelectric pH of beta-L, such features were just noticeable in the absence of particles but were much more pronounced than at pH 7 in the presence of particles. Similar experiments with OA revealed even more pronounced structural features, both in the absence and presence of particles, particularly at pH 5 (close to the isoelectric pH of OA also), producing striking stripelike and meshlike domains. Changes in the dilatational elasticity of the films could be correlated with the variations in the structural integrity of the films as observed via BAM. The results indicate that interfacial area changes of this type, typical of those that occur in food colloid processing, will lead to highly inhomogeneous adsorbed protein layers, with implications for the stability of the corresponding foams and emulsions stabilized by such films. Overall, the experimental results are in broad agreement with the sorts of trends predicted by earlier computer simulations of protein films subjected to such compression and expansion.

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Section: Resultssupporting

confidence: 72%

Section: Resultsmentioning

confidence: 99%