Study On The Antibacterial Activities Of Fenton-Like NiCoFe-MOFs Catalysts Against Foodborne Pathogens

Foodborne pathogen,as a major hidden risk,usually exists in food processing and circulation and causes foodborne diseases.To protect the consumers'health against the microbial safety accidents,a large number of antibacterial agents have been developed,such as antibacterial peptides,chemical disinfectants,quaternary ammonium salts and TiO₂,which have disadvantages of low sterilization efficiency,poor stability,high cost,high toxicity,and drug resistance.Metal-organic frameworks(MOFs),as porous nanostructures connected by metal nodes and organic ligands,provide well-dispersed metal centers and controllable rate of ion release,accelerating efficient sterilization.Furthermore,mixed-metal MOFs can effectively improve the MOFs performance due to the synergistic effect of two or more metal active centers.In order to improve the antibacterial performance of MOFs,this study prepared NiCoFe-MOFs with Fenton-like catalytic activity and antibacterial property to construct an antibacterial system based on Fenton-like catalytic reaction for Staphylococcus aureus(S.aureus)and Escherichia coli(E.coli).Combined with coating preservation technology,functional coating based onNiCoFe-MOFs was studied for the storage and preservation of fresh-cut apples.The main results of this thesis are as follows:(1)Preparation and performance study of NiCoFe-MOFs.By adjusting the content of metal precursors,NiCoFe-MOFs with different Ni/Co/Fe ratios were prepared by the one-pot method,and then the scanning electron microscopy(SEM),transmission electron microscope(TEM),X-ray photoelectron spectroscopy(XPS),and fourier transform infrared spectroscopy(FT-IR)were used to characterize materials.The results showed that two MOFs with different Ni/Co/Fe ratios have been successfully prepared,and the three metal elements were uniformly distributed in the nanostructures.Ni₆Co₃Fe₁-MOF showed nano-flowers morphology with uniform size(about 2?m)and good dispersibility;Ni₁Co₁Fe₁-MOF showed three-dimensional foam-like network structures connected by nanofibers.By comparing the catalytic activity and antibacterial property of the twoNiCoFe-MOFs,it was found that both Ni₆Co₃Fe₁-MOF and Ni₁Co₁Fe₁-MOF had significant Fenton-like catalytic activity,and the Ni₁Co₁Fe₁-MOF performed better than Ni₆Co₃Fe₁-MOF.In addition,the MIC of Ni₆Co₃Fe₁-MOF and Ni₁Co₁Fe₁-MOF were 200 and 300?g/m L,respectively.(2)Construction and optimization of NiCoFe-MOFs antibacterial system based on Fenton-like catalytic reaction.S.aureus and E.coli were selected to test the antibacterial performance ofNiCoFe-MOFs/H₂O₂ catalytic system.The results showed that 100?g/m L ofNiCoFe-MOFs with 0.1 m M of H₂O₂ could achieve the best antibacterial effect after treating 2 h,casing the bactericide rates of Ni₆Co₃Fe₁-MOF and Ni₁Co₁Fe₁-MOF against S.aureus were 89.24%and98.54%,and against E.coli were 95.81%and 97.70%,respectively.Moreover,the antibacterial performance of Ni₁Co₁Fe₁-MOF was better than Ni₆Co₃Fe₁-MOF.Then,the intracellular ROS showed that,after being treated with H₂O₂ and Ni₁Co₁Fe₁-MOF,the ROS in S.aureus and E.coli were about 7 times of those treated with Ni₁Co₁Fe₁-MOF alone under the optimal antibacterial conditions,indicating that the generating of reactive oxygen species was the main reason for the significant increase in antibacterial property.Finally,the cytotoxicity of Ni₆Co₃Fe₁-MOF and Ni₁Co₁Fe₁-MOF was studied and the results indicated that both MOFs had not obvious cytotoxicity.(3)Study on the storage and preservation of fresh-cut apples based on the preparation of sodium alginate/Ni₁Co₁Fe₁-MOF composite coating.A functional sodium alginate/Ni₁Co₁Fe₁-MOF composite coating was prepared using Ni₁Co₁Fe₁-MOF(100?g/m L)as an antibacterial agent and sodium alginate coating as a carrier.Then,the composite coating was used for the storage and preservation of fresh-cut apples.The results showed that,the composite coating effectively stabilized the weight,color,hardness and TSS of fresh-cut apples under 4 °,which significantly inhibited the growth and reproduction of E.coli on fresh-cut apples with the addition of trace H₂O₂.