Copper-based metal-organic frameworks (BDC-Cu MOFs) as supporters for α-amylase: Stability, reusability, and antioxidant potential

Copper-based metal-organic frameworks (BDC-Cu MOFs) were synthesized via a casting approach using 1,4-benzene dicarboxylic (BDC) as organic ligand and their properties characterized. The obtained materials were then utilized to immobilize the alpha-amylase enzyme. The chemical composition and functional components of the synthesized support (BDC-Cu MOFs) were investigated with Fourier transform infrared spectroscopy (FTIR), the surface morphology was determined with scanning electron microscopy (SEM), and the elemental composition was established with energy dispersive X-ray (EDX) analyses. X-ray diffraction (XRD) was employed to analyze the crystallinity of the synthesized DBC-Cu MOFs. The zeta potentials of DBC-Cu MOFs and DBCCu MOFs@alpha-amylase were determined. The immobilized alpha-amylase demonstrated improved catalytic activity and reusability compared to the free form. Covalent attachment of the alpha-amylase to BDC-Cu provided an immobilization yield (IY%) of 81% and an activity yield (AY%) of 89%. The immobilized alpha-amylase showed high catalytic activity and 81% retention even after ten cycles. Storage at 4 degrees C for eight weeks resulted in a 78% activity retention rate for DBC-Cu MOFs@alpha-amylase and 49% retention for the free alpha-amylase. The optimum activity occurred at 60 degrees C for the immobilized form, whereas the free form showed optimal activity at 50 degrees C. The free and immobilized alpha-amylase demonstrated peak catalytic activities at pH 6.0. The maximum reaction velocities (Vmax) values were 0.61 U/mg of protein for free alpha-amylase and 0.37 U/mg of protein for BDC-Cu MOFs@alpha-amylase, while the Michaelis-Menten affinity constants (Km) value was lower for the immobilized form (5.46 mM) than for the free form (11.67 mM). Treatments of maize flour and finger millet samples with free and immobilized alpha-amylase resulted in increased total phenolic contents. The enhanced antioxidant activities of the treated samples were demonstrated with decreased IC50 values in ABTS and DPPH assays. Overall, immobilization of alpha-amylase on BDC-Cu MOFs provided improved stability and catalytic activity and enhanced the antioxidant potentials of maize flour and finger millet.