Interactions of lipases with milk fat globule membrane monolayers using a Langmuir film balance

The interactions of porcine pancreatic lipase (PPL), milk lipoprotein lipase (MLPL) or lipase from Pseudomonas fluorescens (PFL) with the milk fat globule membrane (MFGM) were compared using a Langmuir film balance. Interaction of these three lipases with MFGM depended on the surface pressure of the MFGM film and thus on its organisation. PFL was able to penetrate the MFGM film compressed at surface pressures up to 30 mN m−1, whereas PPL and MLPL were unable to penetrate MFGM compressed at surface pressures higher than 25 mN m−1. Milk proteose-peptone (PPt), a known milk lipolysis inhibitory agent, was used to strengthen the MFGM film against lipase action. Addition of PPt to an MFGM film prevented PPL penetration, even if the film was compressed at a surface pressure lower than the critical surface pressure determined for this lipase. This confirms that milk lipolysis inhibition by PPt is an interfacial phenomenon.