Study On Chitosan-based Bilayer Composite Coating And Electrospun Nanofibers

Membrane materials based on macromolecular polymers have attracted much attention in the field of preservation.In this paper,chitosan-based bilayer coating and electrospun nanofibers were prepared by layer-by-layer self-assembly and electrospinning technology respectively,and lysozyme was added to achieve synergistic bacteriostasis.Chitosan(CS)and sodium alginate(ALG),two polysaccharides with opposite charge,were used as the film matrix to prepare the embedded lysozyme(LZ)bilayer composite coating ALG-CS+LZ.Characterized the microstructure of the bilayer coating,and evaluated the physical and chemical properties,bacteriostatic properties and freshness preservation properties of the coating.A series of LZ/CS/PVA electrospun nanofibers were prepared by loading different amounts of LZ into CS and PVA substrates.The morphological characteristics and the properties of the fibers were analyzed,which laid a theoretical foundation for the further application of the bilayer and electrospun membranes.The main results are as follows:1.The ALG-CS+LZ bilayer composite coating was prepared by layer-by-layer self-assembly technology,and was studied in characterization and physicochemical properties.The results showed that compared with CS,ALG,CS+LZ monolayer coating,the ALG-CS+LZ bilayer composite coating possessed smooth surface.The surface exhibits a distinct irregular distribution and good stereoscopic effect,and the rough surface facilitated the loading of small molecular substances.The SEM of cross-section,and diagrams of FTIR and XRD showed that theALG and CS+LZ coatings were not simply superimposed in the bilayer composite coating.There were strong interactions between sodium alginate,chitosan and lysozyme molecules.The mechanical properties of the bilayer composite coating were significantly better than ALG coating and closed to CS+LZ coating.Water vapor transmittance,oxygen and carbon dioxide transmittance and light transmittance of bilayer coating were significantly lower than ALG coating,and close to CS+LZ coating.The results indicating that the physical and chemical properties did not decrease after the two layers superimposing.2.Antibacterial effect and mechanism of the bilayer composite coating against Pseudomonas fluorescenans and Shewanella putrefaciens as were studied.The results showed that compared with ALG and CS+LZ monolayer coatings,ALG-CS+LZ bilayer coating had more obvious inhibitory effects on P.fluorescenans and S.putrefaciens,and had a certain bactericidal effect at the initial 12 hours.Bilayer composite coating led to more leakage of nucleic acid and electrolyte,damaged the integrity of bacterial cell membrane and increased the permeability of cell membrane.By destroying or inhibiting proteins or enzymes and hindering their synthesis which maintain the normal life activities of cells,the bilayer coatings inhibited the growth of P.fluorescenans and S.putrefaciens.3.The turbot fish fillets treated with ALG,CS+LZ monolayer coating and ALG-CS+LZ bilayer composite coating were stored at 4℃.The changes of total bacterial colonies(TVC),pH value,volatile base nitrogen(TVB-N),thiobarbituric acid(TBARS),K value,texture and low field NMR were examined every 3 days to evaluate the freshness and quality of turbot fillets during storage.The results showed that compared with ALG and CS+LZ monolayer coatings,the ALG-CS+LZ bilayer composite coating more effectively inhibited the growth of spoilage microorganisms in the turbot.The increase of pH,TVB-N and K value of fillet were slowed down.It reduced the denaturation of fish protein and water loss,and prolonged the shelf life of turbot fillets by 4 to 6 days.4.Chitosan/polyvinyl alcohol nanofibers(CS/PVA)with different mass ratios was prepared by electrospinning.LZ/CS/PVA nanofibers wasprepared by adding different content of LZ into the CS/PVA solution with good fiber morphology.SEM,FTIR,XRD and DSC were performed to analyze the morphology and characteristics of LZ/CS/PVA nanofibers.The results showed that the addition of LZ affected the morphology uniformity of fiber and the degree of adhesion between fibers.With the addition of LZ,the average diameter of fibers decreased from339.62±92.72 nm(CS/PVA)to 262.10±86.32~283.01 ±96.83 nm(LZ/CS/PVA series fibers).When the LZ content was 0.30% and 0.50%,the fiber morphology was good.There existed molecular interaction among the components of the nanofibers hindering the formation of crystals,resulting in an almost amorphous structure.Addition of LZ improved the thermal stability of the nanofibers,melting point increased from 185.60℃ to 189.30℃~191.00℃.LZ/CS/PVA nanofibers were prepared from safe and non-toxic materials,which have potential application in food industry.