Improvement of activity and stability of Rhizomucor miehei lipase by immobilization on nanoporous aluminium oxide and potassium sulfate microcrystals and their applications in the synthesis of aroma esters

AbstractIn this study, Rhizomucor miehei lipase (RML) was immobilized on the hexagonally-ordered nanoporous aluminium oxide membranes (RML-Al2O3-NP) by adsorption and as protein-coated microcrystals (RML-PCMCs) by simultaneously precipitating RML on micron-sized potassium sulfate crystals (K2SO4) in pre-chilled acetone. The hydrolytic activities of immobilized lipase preparations were investigated in terms of p-nitrophenyl palmitate hydrolysis and their esterification activities were examined for the synthesis of some aroma esters such as butyl acetate, isoamyl acetate, hexyl acetate, heptyl acetate, and geranyl acetate. The immobilization yields were 33.8 and 25.1%, respectively for RML immobilized on Al2O3-NP membranes and potassium sulfate crystals. The catalytic efficiency ratios of RML-Al2O3-NP and RML-PCMCs were 2.3- and 3.9-fold higher than that of the free lipase, respectively in terms of hydrolytic activity. The free lipase was stabilized as 4.1- and 10.5-fold, respectively at 40 and 50 °C when i...