Interfacial complex of α-lactalbumin with oleic acid: effect of protein concentration and PM-IRRAS study.

We used the Langmuir technique to investigate the binding of the bovine α-lactalbumin (BLA III) to the oleic acid (OA) monolayer in gastric conditions (pH 2.0 and 36.6 °C). Both substances are components of the BAMLET complex, which is beneficial to human health. The monolayer studies have been completed with BAM imaging and PM-IRRAS spectra. This paper explores the interfacial behavior of the lipid monolayer in the presence of the protein. It proves that the higher the concentration of protein in the subphase, the higher the increase in the relative surface pressure of the OA monolayer is, until the additional amount of protein affects the maximmum film response. We also discussed the MIP (maximum insertion pressure) value and analyzed the infrared spectra to prove that BLA III interacts with OA at the interface. We focused on the kinetics of the interaction between these components. We noticed that after protein adsorption at the interface (which rate depends on BLA III concentration), the protein penetrates the lipid monolayer, followed by film rearrangement (the protein forces on fatty acid molecules to change their orientation) until finally a stable lipid-protein complex is formed at the air-water interface. This multi-stage process is relevant to the course of a relaxation curve, which demonstrates the monolayer response on protein injection. This paper explores the physicochemical phenomena which fully recognized may open the door to numerous applications of these lipid-protein system. Unlabelled Image • The oleic acid and α-lactalbumin form the interfacial complex at pH 2.0 and 36.6 °C • In the gastric condition, protein penetrates the oleic acid monolayer • The protein molecules induce film rearrangement • Tightly packed monolayer limits the ability of the protein to penetrate the film • The number of protein molecules penetrating the film is finite under given condition [ABSTRACT FROM AUTHOR]