Using lipase activity to probe milkfat globule membranes (MFGM) or interfaces

Abstract

Measurement of lipoprotein lipase activity (as free fatty acid change or accumulation) is accepted as indicative of milkfat globule membrane (MFGM) disruption. However, measurement is confounded by variables unrelated to the MFGM, e.g., microbial quality. To resolve this, a modified approach to using lipase activity to probe MFGM was developed. Methanol (1%, w/w) and lipoprotein lipase (2%, w/w, raw milk) were added to pasteurised milk samples resulting in formation of methyl esters that therefore served as a new and unique signal for lipase gaining access to interfacial fat. Analysis conditions minimised product formation to minimise sample perturbation. The method could detect 1% (w/w) of homogenised milkfat globules blended with native globules, with linear response to 10% (w/w) and saturation above 20% (w/w). The approach was applied to assess MFGM in samples subjected to disruptive treatments (shear, aeration) under different conditions; findings were consistent with previous research, but with greater sensitivity.