In this work α-amylase was immobilized on magnetic FeO 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.

中文翻译：

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交联 α-淀粉酶聚集在聚多巴胺/聚乙烯亚胺修饰的 Fe3O4 磁性纳米颗粒上，可有效水解淀粉

本工作首次通过吸附-沉淀-交联将α-淀粉酶固定在聚乙烯亚胺（PEI）/聚多巴胺（PDA）涂层或3-氨丙基三乙氧基硅烷（APTES）的磁性Fe3O纳米颗粒上。与游离的α-淀粉酶相比，所得的磁性交联α-淀粉酶聚集体（PEI/PDA-M-CLEAs和NM-CLEAs）表现出优异的热稳定性和储存稳定性以及pH稳定性。在25°C储存60天后，游离α-淀粉酶仅保留其初始活性的60%，而PEI/PDA-M-CLEA和NM-CLEA分别保留其初始活性的80%和78%。此外，NM-CLEA和PEI/PDA-M-CLEA表现出良好的可重用性。重复使用6次后，PEI/PDA-M-CLEA和NM-CLEA仍分别保持其初始活性的65%和62%。特别是，PEI/PDA-M-CLEAs和NM-CLEAs表现出比游离α-淀粉酶更高的淀粉水解效率。 PEI/PDA-M-CLEAs和NM-CLEAs水解淀粉的最大葡萄糖当量（DE）值在90分钟内分别达到29.24%和28.79%。然而，即使在150 min内，游离α-淀粉酶水解淀粉的最大DE值也仅为27.89%。磁性交联 α-淀粉酶聚集体可以作为有效的生物催化剂用于麦芽糖浆生产的工业应用。