Abstract
In this work α-amylase was immobilized on magnetic Fe3O4 nanoparticles with polyethylenimine (PEI)/polydopamine (PDA) coating or 3-aminopropyl triethoxysilane (APTES) for the first time via adsorption–precipitation–cross-linking. Compared with the free α-amylase, the resultant magnetic cross-linked α-amylase aggregates (PEI/PDA-M-CLEAs and N-M-CLEAs) exhibited excellent thermal and storage stability as well as pH stability. After storage at 25 °C for 60 days, free α-amylase only retained 60% of its initial activity, while PEI/PDA-M-CLEAs and N-M-CLEAs retained 80% and 78% of their initial activities, respectively. Furthermore, N-M-CLEAs and PEI/PDA-M-CLEAs showed good reusability. After 6 repeated uses, PEI/PDA-M-CLEAs and N-M-CLEAs still maintained 65% and 62% of their initial activities, respectively. Especially, PEI/PDA-M-CLEAs and N-M-CLEAs exhibited higher starch hydrolysis efficiency than free α-amylase. The maximum dextrose equivalent (DE) values of starch hydrolysis by PEI/PDA-M-CLEAs and N-M-CLEAs reached 29.24% and 28.79% within 90 min, respectively. However, the maximum DE values of starch hydrolysis by the free α-amylase was only 27.89% even in 150 min. The magnetic cross-linked α-amylase aggregates could be introduced as effective biocatalyst for industrial applications in production of maltose syrups.
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