Stability of lipase immobilized on O-pentynyl dextran

O-Pentynyl dextran (PyD), an amphiphilic polysaccharide derivative with a degree of substitution (DS) of 0.43 was compared with ion exchange resins Lewatit VP OC 1600, Amberlite XAD 761 and Duolite A568 for immobilization of Lipase from Rhizopus arrhizus by adsorption method. The immobilized enzymes were employed for esterification of octanoic acid with geraniol in n-hexane as model reaction. PyD showed higher lipase adsorption and with 249 μmol min(-1) g(-1) significant higher esterification activity than the other supports (67-83 μmol min(-1) g(-1)). Biocatalysts from all types of supports except PyD became completely inactive within 8 weeks storing at -10 °C while lipase immobilized on PyD retained its full esterification activity for at least 14 weeks. In repeated use, yield decreased rapidly after two cycles for all supports except for PyD. For this biopolymeric support, constantly 90% yield was achieved even after eight cycles, when the biocatalyst was washed with n-hexane and water and then freeze-dried. To achieve this yield, prolonged reaction times were required, partly on the account of an increasing delay period, probably to adapt active conformation, until the reaction starts.