Oil–water interfacial behaviour of different caseins and stability of emulsions: Effect of micelle content and caseins concentrations

This study aimed to investigate the interfacial behaviour of caseins in different micelle content and its effect on the stability of emulsions, including micellar casein concentrate (MCN), calcium caseinate (CaC) and sodium caseinate (NaC). Results revealed that at high protein concentrations (0.5 %–2.5 %), MCN, CaC and NaC exhibited similar interfacial behaviour as well as unfolding rate constants (k1) of 3.11–3.41 × 10−4 (s−1), 2.96–3.35 × 10−4 (s−1) and 2.75–3.27 × 10−4 (s−1), respectively. The interfacial layer formed was dominated by non-micelles, and microscopic images revealed the thickness of the interfacial layer to be 10–20 nm. By contrast, at low concentrations, the differences in the slope of E–π curves and k1 indicated that the micelle content of casein affects protein interfacial behaviour and properties and that micellar casein is involved in the formation of the interfacial layer. The formation of large numbers of droplets during emulsion preparation results in a similar low concentration environment. Cryo-TEM showed adsorption of micellar casein in all three casein-stabilised emulsions, and the amount of adsorption was proportional to the micelle content. NaC has faster adsorption and rearrangement rates due to fewer micelles and more non-micelles, so that NaC forms smaller droplets and more stable emulsions than those formed by MCN and CaC within the range of 0.5 % to 2.0 %.