Interfacial properties, film dynamics and bulk rheology: A multi-scale approach to dairy protein foams.

ABSTRACT

HYPOTHESIS: The effective contribution of interfacial properties to the rheology of foams is a source of many open questions. Film dynamics during topological T1 changes in foams, essentially studied for low molecular weight surfactants, and scarcely for proteins, could connect interfacial properties to protein foam rheology. EXPERIMENTS We modified whey protein isolate (WPI), and its purified major protein ß-lactoglobulin (ß-lg) by powder pre-conditioning and dry-heating in order to obtain a broad variety of interfacial properties. We measured interfacial properties, film relaxation duration after a T1 event and bulk foam rheology. FINDINGS: We found that, for ß-lg, considered as a model protein, the higher the interfacial elastic modulus, the longer the duration of topological T1 changes and the greater the foam storage and loss moduli and the yield stress. However, in the case of the more complex WPI, these correlations were less clear. We propose that the presence in WPI of other proteins, lactose and minerals modify the impact of pre-conditioning and dry-heating on proteins and thereby, their behaviour at the interface and inside the liquid film.