Hydrolysis of an aliphatic monoester in emulsion by swine pancreas lipase: influence of interfacial bile salts molecules upon reaction rate.

The accumulation of four bile salts at the interface between water and n-hexyl laurate is studied. Gibb's interfacial excesses of these salts are calculated, starting from interfacial tension measurements. At the same time, emulsions of the ester are treated by lipase and reactions rates are plotted against the bile salt concentrations present in the water phase of the emulsions. Inhibition by conjugated bile salts appear before the critical micellar concentration is approached. There is no defined relationship between this inhibition and the fraction of interfacial area covered by detergent molecules. In accordance with recent publication, the discussion suggests that the energy level of interfaces is important for lipase action and that, when interfacial tension becomes too small, lipase does not attach to interfaces and appears as inactive.