Immobilization of lipase on hydrophobic MOF synthesized simultaneously with oleic acid and application in hydrolysis of natural oils for improving unsaturated fatty acid production.

The hydrolysis of natural oils (vegetable oils and fats) by lipase has significant applications in food and medicine. However, free lipases are usually sensitive to temperature, pH and chemical reagents in aqueous solutions, which hinders their widespread industrial application. Excitingly, immobilized lipases have been widely reported to overcome these problems. Herein, inspired by lipase interface activation, a hydrophobic Zr-MOF (UiO-66-NH2-OA) with oleic acid was synthesized for the first time in an emulsion consisting of oleic acid and water, and the Aspergillus oryzae lipase (AOL) was immobilized onto the UiO-66-NH2-OA through hydrophobic interaction and electrostatic interaction to obtain immobilized lipase (AOL/UiO-66-NH2-OA). 1H NMR and FT-IR data indicated that oleic acid was conjugated with the 2-amino-1,4-benzene dicarboxylate (BDC-NH2) by amidation reaction. As a result, the Vmax and Kcat values of AOL/UiO-66-NH2-OA were 179.61 µM﹒min-1 and 8.27 s-1, which were 8.56 and 12.92 times higher than those of the free enzyme, respectively, due to the interfacial activation. After treated at 70 °C for 120 min, the immobilized lipase maintained 52 % of its original activity, but free AOL only retained 15 %. Significantly, the yield of fatty acids by the immobilized lipase reached 98.3 % and still exceeded 82 % after seven times of recycling.

Glutamate Oxidase-Integrated Biomimetic Metal-Organic Framework Hybrids as Cascade Nanozymes for Ultrasensitive Glutamate Detection.

The hybrid coupling of biocatalysts and chemical catalysts plays a vital role in the fields of catalysis, sensing, and medical treatment due to the integrated advantages in the high activity of natural enzymes and the excellent stability of nanozymes. Herein, a new nanozyme/natural enzyme hybrid biosensor was established for ultrasensitive glutamate detection. The MIL-88B(Fe)-NH2 material with remarkable peroxidase mimic activity and stability was used as a nanozyme and carrier for immobilizing glutamate oxidase (GLOX) through Schiff base reaction to construct a chem-enzyme cascade detector (MIL-88B(Fe)-NH2@GLOX). The resultant MIL-88B(Fe)-NH2@GLOX exhibited a wide linear range (1-100 µM), with a low detection limit of 2.5 µM for glutamate detection. Furthermore, the MIL-88B(Fe)-NH2@GLOX displayed excellent reusability and storage stability. After repeated seven cycles, MIL-88B(Fe)-NH2-GLOX (GLOX was adsorbed on MIL-88B(Fe)-NH2) lost most of its activity, whereas MIL-88B(Fe)-NH2@GLOX still retained 69% of its initial activity. Meanwhile, MIL-88B(Fe)-NH2@GLOX maintained 60% of its initial activity after storage for 90 days, while free GLOX only retained 30% of its initial activity. This strategy of integrating MOF mimics and natural enzymes for cascade catalysis makes it possible to design an efficient and stable chemo-enzyme composite catalysts, which are promising for applications in biosensing and biomimetic catalysis.

Hierarchical micro- and mesoporous ZIF-8 with core-shell superstructures using colloidal metal sulfates as soft templates for enzyme immobilization.

Metal-organic frameworks (MOFs), with large specific surface area and tunable porosity, have gained lots of attention for immobilizing enzymes. However, the intrinsic open channels of most reported MOFs are generally smaller than 2 nm, which significantly prevents the passage of enzymes, and the diffusion efficiency of substrates and products. Here we report a new hierarchical micro-mesoporous zeolitic imidazolate framework-8 (ZIF-8) with core-shell superstructure (HZIF-8) using colloidal hydrated zinc sulfate (ZnSO4·7H2O) as a soft template for enzyme immobilization. The ZnSO4·7H2O forms an aggregation of colloids due to the self-conglobation effect in methanol, which affords a soft template for the formation of HZIF-8. Cytochrome C (Cyt C) was immobilized in interior of HZIF-8 through entrapment during the formation of HZIF-8. The resultant immobilized Cyt C (Cyt C@HZIF-8) exhibited 4-fold and 3-fold higher activity than free Cyt C and Cyt C encapsulated in conventional microporous ZIF-8 (Cyt C@ZIF-8), respectively. Meanwhile, the Km value of Cyt C@HZIF-8 significantly decreased due to the presence of mesopores compared with Cyt C@ZIF-8, indicating enhanced substrate affinity. After 7 cycles, Cyt C@HZIF-8 still maintained 70% of its initial activity whereas Cyt C@ZIF-8 only retained 10% of its initial activity. Moreover, the obtained HZIF-8 showed outstanding performance in co-immobilization of multi-enzyme for the detection of glucose.

Characterization of aldehydes and hydroxy acids as the main contribution to the traditional Chinese rose vinegar by flavor and taste analyses.

The volatile aroma compounds of traditional Chinese rose vinegar were identified by headspace solid-phase micro extraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) and GC-MS-olfactometry (GC-MS-O), and the metabolites were identified by silylation-GC-MS in this study. A total of 48 and 76 kinds of flavors and metabolites, respectively were detected in this study. Quantitative analysis showed that aldehydes and acids were present in relatively high amounts. Furthermore, the data colleted by the calculated odor activity values (OAVs) suggested that aldehydes are likely to contribute greatly to the aroma of traditional Chinese rose vinegar, especially, nonanal (OAV: 133, rose), 3-methyl-butanal (OAV: 57, apple-like), decanal (OAV: 23, orange peel), heptanal (OAV: 17, fruity), and dodecanal (OAV: 4-9, violet scents). Moreover, among the detected nonvolatile acids, 14 kinds of hydroxy acids, such as lactic acid, citric acid, 3-phenyllactic acid (PLA) and d-gluconic acid were detected in rose vinegar. The acids provide a well buffer system, not only greatly reduce the irritation of acetic acid, but also improve the flavor of rose vinegar. This study suggests that the fragrance and sour notes in rose vinegar are from aldehydes and hydroxy acids.