A physicochemical investigation of two phosphatidylcholine/bile salt interfaces: implications for lipase activation

Within the gastrointestinal tract ingested lipids are broken down into their constituent mono-acylglycerides and fatty acids by the enzyme family of lipases. In this study we have investigated the interfacial composition and structure of two phospholipid/bile salt (BS) systems that display significant differences in the duration of the lag phase of porcine pancreatic lipase kinetics. The interfacial tension of the single BSs, and their binary mixtures with phospholipid is reported at an n-tetradecane/water interface as a function of phospholipid mole fraction and total surfactant concentration. The structuring of the interface was probed by characterisation of the thin liquid film formation, thickness and stability. Lateral interactions were quantified by measurement of the diffusion coefficient of a probe fluorophore. We conclude that interfacial tension was not a factor in lag time duration as there was no significant difference in the minimum interfacial tension for the phosphatidylcholine (PC)/sodium taurocholate and the PC/sodium taurodeoxycholate system. No correlation was found between lag phase duration and the physiochemical properties of the interface, i.e. lateral diffusion, thin liquid film formation or interfacial tension. This is in agreement with our previous study that the lag time duration was directly related to the phospholipid content of the interface.