A study of hydrolases stability in supercritical carbon dioxide (SC-CO2)

The thermal stability and stability against pressurization/depressurization steps of lipase from Pseudomonas sp. and lipase from Candida cylindracea have been compared with data of other enzymes previously published. Hydrolases (lipases and esterases, crude preparations) with disulfide bridges have a lower degree of inactivation after several pressurization/depressurization steps but no better thermal stability (75°C, 150 bar, 24 h) compared to an enzyme without cystines. A higher loss in enzyme activity was observed after 30 depressurization steps from the liquid phase (56.3% loss of the initial activity) than from the supercritical phase (36.1% loss). Twenty phase transition cycles (liquid–supercritical and supercritical–liquid) do not cause more enzyme inactivation (86.8% residual activity) than simple incubation at 20°C (95.3%) or 65°C (82.1%). Comparing a crude form of lipasefrom Aspergillus niger and a preparation with higher activity, it turns out that the stability of the crude enzyme (92% of initial activity) against 30 pressurization/depressurization steps is similar to that of the purer preparation (102%). Also, thermal stabilities do not differ greatly (108% vs. 97%). Fluorescence spectra indicate no conformational change oflipase from Aspergillus niger after SC-CO2 treatment.