Isotherm, kinetic, mechanism and thermodynamic studies of adsorption of a microbial lipase on a mesoporous and hydrophobic resin

Abstract

Lipase from Thermomyces lanuginosus (TLL) was immobilized via physical adsorption on mesoporous poly-(styrene-divinylbenzene) resin (PSty–DVB). The influence of pH, ionic strength, temperature, initial protein loading, and contact time on the adsorption process and catalytic properties of the biocatalysts was systematically investigated. The catalytic properties of the biocatalysts were determined in the hydrolysis of olive oil emulsion and immobilized protein concentration. Maximum adsorption capacity of 133.9±1.3mg of protein/g of support using initial protein loading of 150mg/g was observed after 900min of incubation at 5mM buffer sodium acetate pH 5.0 and 25°C. This biocatalyst presented hydrolytic activity of 443.0±25.2IU/g of support. Moreover, high esterification activity and operational stability in cetyl linoleate (wax ester) synthesis in a solvent-free system (conversion of 90.5±0.6% after five cycles of reaction of 30min each) was also observed. This biocatalyst showed better catalytic activity than commercial immobilized TLL (Lipozyme TL–IM) in wax ester synthesis (conversion ≈87% after 120min of reaction). Thermodynamic analysis showed that the immobilization was a spontaneous and a physisorption process. The equilibrium adsorption data were fitted to the Sips isotherm model. The results of kinetic study showed that the adsorption process was described by a pseudo-first-order model. This process was influenced by intraparticle and film diffusion. Attenuated total reflection Fourier transform infrared (ATR–FTIR) and scanning electronic microscopy (SEM) analyses were also performed to confirm the adsorption of the enzyme on the support surface.