The
reusability of immobilized lipases, including their hydrolysis
activity, is greatly affected by lipase leakage, mass transfer channel
blockage, and compound deposition on the outside surface. In this
study, Candida antarctica lipase B (CALB) was immobilized on Fe3O4 nanoparticle-polyacrylonitrile (PAN) composite
magnetic beads through phase inversion (L/FP). The hydrolysis activity
of lipase was investigated using p-nitrophenyl palmitate
(p-npp) as a model ester. To overcome the limitations
of immobilized lipase in ester hydrolysis, three modification strategies
were employed. First, lipase was covalently immobilized on Fe3O4 nanoparticles modified with methallyl (M9) and
chloro (M13) silane modifiers, which exhibited faster immobilization
with reduced lipase leaching and higher activity expression and stability.
Second, poly(ethylene glycol) (PEG6000) and polylactic acid (PLA)
were added to the precursors to physically modify the composite structures
of L/FP, resulting in modified beads with larger specific surface
area (15.26 m2·g–1) and smaller
average pore size (19 nm). The modified beads, L/FP-9-M and L/FP-13-M,
demonstrated superior reusability in long-term hydrolysis activity
over 250 cycles. L/FP-9-M retained 63 and 34% of the initial activity
at the 100th cycle and the 250th cycle, respectively. L/FP-13-M retained
55 and 36% of the initial activity at the 100th cycle and the 250th
cycle, respectively. Furthermore, even after 250 repeated uses, the
unit activities (U·gsupport
–1) of
both L/FP-9-M and L/FP-13-M remained higher than the initial activity
of Novo 435.