MALDI imaging of enzymatic degradation of glycerides by lipase on textile surface.

Most modern laundry detergents contain enzymes such as proteases, amylases, and lipases for more efficient removal of stains containing proteins, carbohydrates, and lipids during wash at low temperature. The function of the lipases is to hydrolyse the hydrophobic triglycerides from fats and oils to the more hydrophilic lipids diglycerides, monoglycerides and free fatty acids. Here, we use MALDI imaging to study the effect of enzymatic degradation of triglycerides by lipases directly on the textile surface. Textile samples were created by using swatches of different textile blends, adding a lipid stain and simulating washing cycles using well-defined detergents with lipase concentrations ranging between 0 and 0.5ppm. After washing, the textile swatches as well as cryo-sections of the swatches were imaged using MALDI imaging in positive ion mode at pixel sizes of 15-75μm. Similar samples were imaged by DESI-MSI for comparison. Despite the rough surface and non-conductive nature of textile, MALDI imaging of glycerides on textile was readily possible. The results show extensive enzymatic degradation of triglycerides into diglycerides, and images suggest that this degradation takes place in a quite heterogeneous manner as also observed in images of cross-sections. DESI-imaging reveals the same kind of enzymatic degradation, but with a more homogeneous appearance. While the enzymatic degradation is exemplified in a few images, the overall degradations process was monitored by extraction of ion intensities from 298 individual ion masses of mono-, di- and triglycerides and free fatty acids. MALDI imaging of glycerides was possible directly from a textile surface, allowing visualization of the enzymatic degradation of fatty stains on textile during the laundry process. The images showed an inhomogeneous presence of diglycerides after lipase treatment both in planar images of the textile surface as well as in cross-sections suggesting a non-uniform enzyme effect or extraction of the lipase reaction products from the textile.