Study of Oxygen Transfer across Milk Proteins at an Air–Water Interface with Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) combined with a Langmuir trough was used for studying oxygen transfer across protein films at an air–water interface. The method allows the comparison of the oxygen permeability of different emulsifiers without any concerns of interference of atmospheric oxygen. Two milk proteins, β-lactoglobulin and β-casein, were compared, and the permeabilities obtained were for β-casein PD ≈ 2.2 × 10^–7 cm²/s and for β-lactoglobulin PD ≈ 0.6 × 10^–7 cm²/s, which correspond to the lowest limit of the diffusion coefficients and are 2 orders of magnitude lower than the diffusion coefficient of oxygen in water, yet several orders of magnitude higher than previously reported for milk protein films. The method allows characterization of the oxygen barrier properties of liquid interfacial films, which is of crucial importance for understanding the role of the interface in the inhibition of oxygen transport and developing modified interfaces with higher oxygen blocking efficacy.