The purpose with the proposed project is to provide a better understanding of structural changes in interfacial lipid layers due action of lipolytic enzymes. In this study we will use the recently developed spin-freeze-thaw technique to form stable, uniform oil films with thicknesses of ~2 μm by spin coating the oil onto hydrophobically modified silicon substrates. This opens up a unique possibility to form a well-defined and native-like triglyceride substrate for lipase that allows detailed study of the lipase adsorption at a relevant substrate as well as the structure and the lipid phase transition that occurs as a consequence of the lipolytic activity. Bothwild type and inactive mutants of Thermomyces lanuginosus lipase (TLL), we will be able to separate the consequences of enzyme adsorption and interaction with the interface from those arising from the lipolytic activivity.