Adsorption from lipase-surfactant solutions onto methylated silica surfaces

Abstract

In situ ellipsometry was used to study the adsorption/desorption of highly purified lipase from Humicola lanuginosa in mixtures with surfactants, at the solid/liquid interface. The effect of the surfactant was studied both when it was allowed to adsorb in mixture with lipase and when added after lipase adsorption. Silica surfaces, totally or partially methylated, were used and the surfactants were SDS (anionic), C 12E 5 and a commercial alcohol ethoxylate (AE) (both nonionic). The experiments were carried out so as to simulate a laundry process and the pH throughout the study was kept at 9 by means of Tris-HCl buffer. From the results it was shown that the lipase did not adsorb until the diluted, that is during the rinsing period. This was found for all the lipase-surfactant mixtures in the study. However, the amount of lipase adsorbed was larger after rinsing in mixture with SDS, compared with C 12E 5. The results from addition of surfactant after lipase adsorption indicated that the lipase was replaced by surfactant. This was found for SDS and C 12E 5 at both the hydrophobic surface and the surface with intermediate hydrophobicity.