Immobilization and stability of lipase from Mucor racemosus NRRL 3631

The lipase from Mucor racemosus NRRL 3631 was partially purified by fractional precipitation using 60% ammonium sulfate, which resulted in a 8.33-fold purification. The partially purified lipase was then immobilized using different immobilization techniques: physical adsorption, ionic binding, and entrapment. Entrapment in a 4% agar proved to be the most suitable technique (82% yield), as the immobilized lipase was more stable at acidic and alkaline pHs than the free enzyme, plus 100% of the original activity was retained owing to the thermal stability of the immobilized enzyme after heat treatment for 60 min at 45 degrees Celsius. The calculated half-lives (472.5, 433.12, and 268.5 min at 50, 55, and 60 degrees Celsius, respectively) and the activation energy (9.85 kcal/mol) for the immobilized enzyme were higher than those for the free enzyme. Under the selected conditions, the immobilized enzyme had a higher K(m) (11.11 mM) and lower V(max) (105.26 U/mg protein) when compared with the free enzyme (8.33 mM and 125.0 U/mg protein, respectively). The operational stability of the biocatalyst was tested for both the hydrolysis of triglycerides and esterification of fatty acids with glycerol. After 4 cycles, the immobilized lipase retained approximately 50% and 80% of its original activity in the hydrolysis and esterification reactions, respectively.