Interfacial network formation by casein blends in the presence of Ca2+ is dominated by β- and κ-casein

Summary

With the increasing interest in precision fermentation for food purposes, the opportunity arises to produce individual casein fractions or specific blends based on the requirements of an application. Therefore, the functionality of individual casein fractions has gained attention in academia and industry. This study focused on the air-water interfacial functionality of individual bovine casein fractions in casein blends, to serve as a benchmark for precision fermented casein fractions. With oscillating bubble tensiometry, we showed that the interfacial behavior of a milk-like casein blend of α_s1-, α_s2-, β-, & κ-casein (ratio 4:1.1:3.8:1.3) was dominated by the β- and κ-casein fractions through the formation of a disordered solid-like viscoelastic interface. The presence of Ca²⁺ in the buffer was essential; Without Ca²⁺, the casein blend formed a weak interfacial microstructure where the viscoelastic modulus was dominated by exchange between bulk and interface. The interfacial microstructure was imaged with Langmuir-Blodgett deposition followed by atomic force microscopy. Here we showed that the interfacial structure of β+κ-casein was highly similar to the milk-like casein blend. In the presence of Ca²⁺ in the buffer, the interfacial microstructure of the casein blend was shown to be more connected and homogeneous compared to a buffer without Ca²⁺. Thereby highlighting the importance of the phosphoserine residues in β-casein. These results show the opportunity to mimic the interfacial functionality of a milk-like casein blend with only a blend of β+κ-casein but that the presence of phosphoserine residues in β-casein is essential for the formation of a stiff interfacial network.