| Food waste and safety issues caused by foodborne pathogens should not be ignored.Using bactericidal food packaging films to pack food is one of the effective methods to prevent food from being contaminated by foodborne pathogens.However,the existing sterilization packaging films is faced with the problems of unintelligent killing,not instantaneous killing,unsustainable killing and low-efficacy killing.The bactericidal functional substances in the packaging films are also faced with the challenge of high cost and poor stability.In order to solve these problems,this paper prepared four different types of films by nanotechnology.The bactericidal efficacy of the films and corresponding bactericidal mechanism were explored.Finally,the feasibility of the films for fruit preservation was comprehensively evaluated.The main research contents and results are as follows:1.Study on the preparation and sterilization mechanism of self-activated filmsIn order to solve the problem that the existing sterilization packaging films is not intelligent,the nano-flake-graphite carbon nitride/chitosan nanocomposite films were prepared by electrostatic self-assembly method.Scanning electron microscopy,atomic force microscope,fourier transform infrared spectroscopy,zeta potential,rheometer,and X-ray diffraction were used to characterize the morphology and structure of the films and the rheological properties of the film forming solution.Thermogravimetric analyzer,texture analyzer and contact angle meter were applied in testing the physicochemical properties of the films.Bactericidal efficiency and measurement of inhibition zone were used to evaluate the bactericidal performances of the films.Storage test were employed to verify the preservation effect of the films on tangerines.The safety of the films was verified by hemolysis and cell experiments.The results showed that the overall performance of CS-NCN-30 film was the best.Intermolecular hydrogen bonding and electrostatic interactions contributed to the uniform and dense structure of the films with Ra of 4.8 nm and Rq of 6.2 nm.The residual heat of the film was 45.6%and its contact angle was 102.4°.This film could self-activate to kill 99.8±0.26%of E.coli and 99.9±0.04%of S.aureus,and could effectively preserve tangerines for 24 days.Next,nano-flake-graphite carbon nitride/molybdenum disulfide nanoparticles/konjac glucomannan composite film was constructed.Scanning electron microscopy,transmission electron microscopy,high-resolution transmission,high angle annular dark field,element mapping and DSC were used to characterize the films.Inhibition zone test,bacterial fixation observation and infrared thermal imaging were used to study the bactericidal properties and mechanisms of the films.The results showed that the overall performance of KCNMo-10 film was the best.This film inhibition zones of 12.3±1.5 mm toward E.coli and 20.6±1.5 mm toward S.aureus,respectively.Also,this film could effectively preserve cherry tomatoes for 18 days.2.Study on the preparation and sterilization mechanism of quasi-pasteurization filmsBased on the study of self-activated films,in order to further solve the problem that the existing sterilization packaging films unable to kill bacteria instantaneously,the nano-flake-graphite carbon nitride/graphene oxide/konjac glucomannan functional films was prepared by solvent casting method.Scanning electron microscopy,infrared spectroscopy,Raman spectroscopy,rheometer,DSC,contact angle meter,texture analyzer and water vapor transmittance were used to test the morphology,structure,thermal properties,mechanical properties and hydrophobic properties of the films.Inhibition zone test,bacterial immobilization observation,infrared thermal imaging and free radical scavenging tests were used to study the function of quasi-pasteurization and its bactericidal mechanism.The results showed that the overall performance of KCNGO-10 film was the best.This film exhibited excellent thermal stability with structural failure temperature of 303°C.The tensile strength and elongation at break were 29.4±3.5 MPa and 6.9±0.4%,respectively,and it had contact angle of 77.6°.This film could raise to 55±1°C in 4 min and had inhibition zones of 15.3±1.2 mm toward E.coli and 21.0±2.6 mm toward S.aureus,respectively.The generation of hydroxyl radicals,superoxide radicals and heat were the mechanism of instantaneous killing of the films.This film could effectively maintain the“fresh-like”characteristics of the fruit in 24 days and was safe.3.Study on the preparation and sterilization mechanism of sustained-release filmsBased on the study of quasi-pasteurization films,in order to further give the films sustained-release function and solve the problem of unsustainable killing of the existing sterilization packaging films,the hollow graphite carbon nitride/curcumin/chitosan nano composite films were prepared by incorporating curcumin into nano-hollow graphite carbon nitride.Scanning electron microscope,transmission electron microscope,atomic force microscope,fourier transform infrared spectroscopy and XRD were used to characterize the films.Texture analyzer,TGA,and contact angle meter were used to test the mechanical properties,thermal properties and hydrophobic properties of the films,respectively.Cumulative slow release test,bactericidal efficiency and inhibition zone measurement were used to study the release characteristics,bactericidal activity and mechanism of the films.The results showed that residual heat of the film was 51.7%,and the average contact angle and water vapor transmittance were 105.83°and g·mm·（m2·h·k Pa）-1,respectively.This film had bactericidal efficiency of 83.3±1.0%and inhibition zone of 8.0±1.0 mm toward E.coli.And it also had bactericidal efficiency of 85.2±5.5%and inhibition zone of 8.7±1.5 mm toward S.aureus.This film showed p H-responsive release characteristics and sustained bactericidal activity,and could effectively preserve millet bananas for 10 days.4.Study on the preparation and sterilization mechanism of high bactericidal efficacy filmsBased on the study of sustained-release films,in order to further fight with the threat of drug-resistance of foodborne pathogens and solve the problem of low bactericidal efficacy of the existing sterilization packaging films,inspired by the layer-by-layer stacking of thylakoids in natural chloroplasts and the focusing effect of magnifying glass,thylakoid-like nano-triple-shelled graphite carbon nitride-based film was prepared.Scanning electron microscope,XRD,BET,UV-vis diffuse reflectance,inhibition zone measurement,bacterial fixation observation,coagulase,BCA protein,nucleic acid content,ATP content,and ATPase activity test were used to study the bactericidal activity and killing mechanism of the films.The results showed that this film had excellent bactericidal efficacy,which was based on the mechanism of enhanced photodynamic and bacterial metabolic balance intervention.Secondly,inspired by the coronal morphology of COVID-19 and its super ability to cross cell membranes.A coronal nano-triple-shelled graphite carbon nitride-based film was prepared.Transmission electron microscopy,high-resolution transmission electron microscopy,free radical scavenging experiments,ESR,fluorescent live and dead bacteria staining,membrane potential assay,infrared thermal imaging,and TMB color development were used to study the bactericidal efficacy and killing mechanism of the films.The results showed that this film showed high bactericidal efficacy,which originated from the multi-synergistic killing mechanism based on its super membrane penetration ability,photodynamic sterilization,oxidase-like activity,photothermal and thermal insulation effects. |
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