Chemistry and Physics of Lipids 133 (2005) 37–49 Enzymatic lipid removal from surfaces—lipid desorption by a pH-induced “electrostatic explosion” Torben Snabe, Maria Teresa Neves-Petersen, Steffen Bjørn Petersen ∗ Department of Physics and Nanotechnology, Biostructure and Protein Engineering Group, Aalborg University, DK-9000 Aalborg, Denmark Received 1 August 2003; received in revised form 12 August 2004; accepted 24 August 2004 Available online 12 October 2004 Abstract Removal of lipidic molecules from surfaces can be accomplished using detergents containing lipases. Surface cleaning is usually performed under alkaline conditions due to increased solubility of the hydrolysis products, especially free fatty acids. This paper shows that removal of a triacylglycerol film from a surface can be dramatically enhanced in a sequential system where pH is shifted to alkaline conditions after an initial lipolytic reaction period at or below neutral pH. Data from three different biophysical techniques, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance with dissipation monitoring (QCM-D), and total internal reflection fluorescence spectroscopy (TIRF) clearly show the effects of such cleaning procedure. Initially the reaction is carried out at pH below the pK a value of the fatty acids formed upon triacylglycerol hydrolysis, and the protonated fatty acids accumulate in the film. The mechanism of lipid removal, induced by increasing pH to a value above the fatty acid pK a , is explained by a burst caused by electrostatic repulsion between rapidly ionised fatty acids, i.e. by an “electrostatic explosion”. Performing the initial hydrolysis at pH 6 and the subsequent rinse at pH 10, using triolein as model substrate, lipid removal from surfaces by both commercial detergent lipases and non-commercial lipases was significantly improved compared to a reaction at constant pH 10. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Lipase activity; Lipid removal; Lipase adsorption; Triacylglycerol; ATR-FTIR; QCM-D; TIRF 1. Introduction A major problem when cleaning surfaces is the re- moval of adsorbed lipid deposits, which often contain ∗ Corresponding author. Tel.: +45 96358469; fax: +45 96359129. E-mail address: sp@nanobio.aau.dk (S.B. Petersen). URL: http://www.nanobio.aau.dk (S.B. Petersen). oily, longchained, and water-insoluble triacylglyc- erols. Detergent formulations usually contain lipolytic enzymes (lipases, formally triacylglycerol lipases, E.C. 3.1.1.3), which degrade triacylglycerols into free fatty acids, di- and mono-acylglycerols, and possibly glycerol. These hydrolysis components, especially the fatty acids, are more water soluble compared to triacylglycerols (Fujii et al., 1986). With aid from 0009-3084/$ – see front matter © 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.chemphyslip.2004.08.005