Foam stabilized by large casein micelle aggregates: The effect of aggregate number in foam lamella

Abstract

In this study, a casein micelle aggregate dispersion (CMAD) with average particle size of 6.7 ± 0.5 μm was prepared using ultracentrifugation, pelleting, milling and redispersion and mixed with a casein micelle dispersion (CMD) with average particle size of 0.13 ± 0.02 μm in varying ratios (0, 25%, 50%, 75% and 100% CMAD, v/v). The effect of particle concentration and size of casein micelle aggregates (CMAs) on foam stability and thin film stability was investigated. Results showed that foam stability increased with increasing bulk concentration of CMAs. The actual aggregate concentration in foam lamella which account for an improved foam stability was well quantified using optical microscopy. Besides, the thin film measurements showed an increase in film rupture times with increasing aggregate concentration in the thin films for diluted dispersions, which confirmed the strong link between aggregate number in foam lamella and corresponding foam stability. At the protein concentration studied (2%), the aggregates did not form a gel network in the lamella but were randomly distributed over the film. The film and foam stabilization by CMAs is ascribed to the fact that they effectively divided the whole film into film elements with smaller radius, resulting in a smaller critical film thickness for film rupture. Another effect is that film drainage can be slowed down by an effective suction pressure in the film due to the curvatures induced by the wetting of hydrophilic particles. In conclusion, aggregated particles of casein micelles around 5–10 μm prepared in this research could be applied to enhance the functional properties of dairy foams.