Enzymatic degradation of poly-l-lysine-polygalacturonic acid multilayers

The action of polygalacturonase on layer-by-layer deposited multilayer films composed of poly-l-lysine and polygalacturonic acid was examined using a quartz crystal microbalance with dissipation monitoring (QCMD), dual polarisation interferometry (DPI) and atomic force microscopy. These techniques were used to determine changes in polymer mass, density, thickness, morphology and hydration of the multilayers in response to enzymatic degradation.The degradation of the multilayer films by polygalacturonase was studied in the range 0.01–1.0 activity units mL−1 (U mL−1). The QCMD and DPI results show that addition of polygalacturonase solution with an activity of 1 U mL−1 led to an almost complete disintegration (over 80% mass loss) of the PLL–PGA structure within 20 min, whilst a polygalacturonase solution with the lowest activity had negligible effect on PLL–PGA films. It was found that the multilayer film with PLL uppermost slows the degradation, an effect which persisted throughout the course of the degradation.