Analysis of Enzymatic Hydrolysis Kinetics

BACKGROUND A thermophilic lipase?producing Geobacillus thermodenitrificans strain AV?5 was isolated from the Mushroom Spring of Yellowstone National Park in WY, USA and studied as a source of lipase for transesterification of vegetable oils to biodiesel. RESULTS A maximum activity of 330 U mL?1 was produced on 2% (v/v) waste cooking oil at 50 °C, pH 8, aeration rate of 1 vvm and agitation speed of 400 rpm. However, the higher lipase productivity (14.04 U mL?1 h?1) was found at a volumetric oxygen transfer coefficient (kLa) value of 18.48 h?1. The partially purified lipase had a molecular weight, temperature and pH optimum of 50 kDa, 65 °C and pH 9, respectively, and was thermo?alkali stable: at 70 °C, it retained 81% activity and 45% stability; at pH 10 it lost only 15% and 2.6% of its maximum activity and stability, respectively. Enzyme kinetic studies with p?nitrophenyl laurate as substrate revealed high substrate specificity (km of 0.440 mmol L?1) and kinetic activity (vmax of 556 nmol mL min?1) of lipase. CONCLUSIONS The kLa was found to be highly dependent on aeration and agitation rates. Following optimization of fermentation medium and parameters, a 7.5?fold increase in lipase production by G. thermodenitrificans was attained. The lipase activity and substrate specificity (as km) are among the highest reported in the literature for bacterial lipases. It was demonstrated that the enzyme can produce biodiesel from waste cooking oil with a conversion yields of 76%. © 2015 Society of Chemical Industry