| Popis: |
Lipases are important to high value product synthesis, modification, and enhancement. However, they are often unstable above 40 °C. While most current applications of high hydrostatic pressure (HHP) are for inactivating deleterious enzymes, there is evidence that HHP can stabilize and increase activity of some enzymes. This study examines the apparent kinetics of immobilized lipase-catalyzed synthesis of isoamyl acetate at HHP in hexane. HHP reduced thermal inactivation of lipase by up to 152% after 4 h at 80 °C and 400 MPa when compared to incubations at low pressure. No significant differences were found in activation energy (Ea) at different pressures, irrespectively of the pressurization and heating sequence, and were between 35.7 ± 3.5 and 47.8 ± 8.2 kJ mol−1, depending on the method. In all methods utilized, activity at 63.5 and 80 °C at 400 MPa was greater (from about 20 to 96% increase) than at low pressure. Activity increased by 110% at low pressure versus a 239% increase at 350 MPa when the temperature was increased from 40 to 80 °C. Increasing pressure up to 350 MPa increased lipase activity while pressures greater than 350 MPa maintained or decreased lipase activity. Activation volume (ΔV≠) appeared negative between ambient pressure and 200 MPa in contrast to a positive ΔV≠ between 300 and 600 MPa. Apparent ΔV≠ was 14.3 ± 1.7 or 15.2 ± 2.2 cm3 mol−1 at 40 or 80 °C, respectively, between 300 and 500 MPa. |
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