Covalent immobilization of organic solvent tolerant lipase on aluminum oxide pellets and its potential application in esterification reaction

This study was carried out to covalently immobilize the partially purified lipase from Bacillus sp. DVL2 on glutaraldehyde-activated aluminum oxide pellets and subsequently use the immobilized enzyme for esterification of oleic acid and ethanol. The immobilization process parameters were optimized through response surface methodology. Under optimized conditions, maximum immobilization yield of the enzyme was 78.20%. The immobilized lipase could be reused for 5 consecutive cycles without any loss of enzyme activity. However, the enzyme showed 75% residual activity after 10th cycle. The stability of the immobilized enzyme towards pH, temperature and organic solvents was enhanced as compared with its soluble counterpart. Higher values of half-lives, D-values, enthalpy and free energy change after covalent immobilization implied an improvement in enzyme stability. The Km and Vmax values of the enzyme were enhanced after immobilization. The immobilized lipase was found to be most stable in DMSO followed by toluene, hexane and xylene, exhibiting more than 90% residual activity in these solvents after 24 h of incubation. The immobilized lipase was more efficient in catalyzing the esterification between oleic acid and ethanol in hexane. The formation of ethyl oleate was confirmed by TLC and 1H NMR spectroscopy.