Preparation And Properties Of Chitosan Nano-TiO₂ Composite Coating Film

In the process of post-harvest storage,the quality of fruits and vegetables is deteriorated due to aging and decay,which not only causes serious economic loss,but also has potential harm to human health.In recent years,the development of organic/inorganic composites suitable for fresh-keeping of fruits and vegetables by using organic materials and inorganic nanomaterials has attracted wide attention.In this paper,nano-chitosan was prepared by ion crosslinking method,and its surface morphology,thermal stability and antimicrobial properties of chitosan nanoparticles were analyzed.Then,the physical properties and antibacterial properties of chitosan-based composite coatings with different concentrations of nano TiO₂were investigated.Finally,the antibacterial properties of chitosan-nano TiO₂-nano chitosan composite coatings solution under LED photocatalysis were studied.The main conclusions are as follows:?1?The optimal preparation process of nano-chitosan by response surface analysis method is as follows:chitosan concentration was 0.76 mg·mL^-1,tripolyphosphate concentration was 0.77 mg·mL^-1,the volume ratio of chitosan to sodium tripolyphosphate was4.11:1,and the pH value of chitosan solution was 5.0.Under these conditions,the particle size of nano-chitosan was 119.2 nm and Zeta potential was 22.8 mV.The nano-chitosan was characterized by microscopy,nanoparticle size analyzer and thermogravimetric analyzer.The results showed that the prepared nano-chitosan was uniform in size,regular spherical and stable in thermal properties.?2?The interaction between nano-chitosan and Bovine Serum Albumin?BSA?showed a strong absorption peak at 278 nm,and the intensity of the peak increased with the increase of the concentration of nano-chitosan solution.Antibacterial experiments showed that nano-chitosan had the same minimum inhibitory concentration and minimum bactericidal concentration for E.coli and S.aureus,which were 0.625 and 1.25 mg·mL^-1,respectively.The growth of E.coli and S.aureus was completely inhibited when the concentration of nano-chitosan was higher than 0.6 mg·mL^-1.Compared with the Bacteriostasis of chitosan and nano-chitosan,nano-chitosan has stronger damage to bacterial cell membrane.Fluorescence spectrum analysis showed that the increase of nano-chitosan concentration can enhance the fluorescence intensity of bacterial cell membrane proteins.Antifungal experiments showed that the minimum inhibitory concentration of nano-chitosan on P.steckii was 5 mg·mL^-1.The mycelial growth inhibition experiment showed that nano-chitosan had stronger inhibition on P.steckii than A.oryzae,Nano-chitosan can cause changes in cell membrane permeability of P.steckii and A.oryzae mycelia,and electrolyte leakage in mycelia.?3?The physical properties of the composite membrane prepared by nano TiO₂ particles with different concentrations were characterized by SEM,AFM,FT-IR and XRD.The results showed that nano-TiO₂ particles combined with chitosan to form a composite film.The composite coating film with a nano-TiO₂ concentration of 0.05%is stable in thermal performance.The results of antibacterial experiments showed that when the concentration of nano-TiO₂ was 0.05%and 0.09%,chitosan-nano TiO₂ composite coating showed strong antibacterial activity against E.coli and S.aureus,and the maximum antibacterial circle was generated at this time,which were 11.37±0.76 mm and 13.55±0.35 mm,respectively.When the nano TiO₂ concentration was 0.05%and 0.01%,the chitosan-nano TiO₂ composite membrane had a slight inhibitory effect on P.steckii and A.oryzae,respectively.?4?The results of qualitative photomicrobial experiment of LED photocatalytic chitosan-nano TiO₂-nano chitosan composite coating liquid showed that after the LED light irradiation,the composite coating liquid showed a certain photocatalytic antibacterial effect,in the absence of light,The chitosan,nano-chitosan and nano-TiO₂ in the composite coating solution have synergistic antibacterial action.The quantitative results showed that the composite coating liquid showed complete killing effect on S.aureus.When the combination of red light and blue light and the nano-TiO₂ content was 0.05%,the composite coating liquid had the highest sterilization rate to E.coli,reaching 92.47%.The red,blue and red+blue light treatment groups had E.coli inhibition zone sizes of 11.91 mm,12.25 mm and 14.03 mm,respectively.Photocatalytic composite membranes showed stronger antibacterial activity against E.coli than S.aureus.After 120 h of treatment with red light and blue light,the combined coating solution had a better antibacterial effect on P.steckii and A.oryzae,which were 4.7 mm and 54.8 mm,respectively.