Design Of Multifunctional Antimicrobial Active Packaging Materials And Their Applications In Fruit And Vegetable Preservation

Fruits and vegetables are an integral part of the daily diet and provide rich nutrients for our health.The postharvest fruits and vegetables need to go through packaging,storage,transportation,sale and other links to reach the hands of consumers.However,the transpiration of fruits and vegetables and the relatively closed packaging environment induce the increase of temperature and humidity of fruits and vegetables during the circulation process,thereby activates the activity of pathogens to infect fruits and vegetables,resulting in a large number of fruits and vegetables to rot and deterioration.With the development of new technologies and new materials,the novel active packaging systems have shown unique advantages in the field of food preservation.Compared with traditional food packaging,active packaging can effectively inhibit the growth and activity of postharvest pathogens by adding antibacterial active ingredients,thus prolonging the shelf life of fruits and vegetables.In this paper,in view of the characteristics of fruit and vegetable packaging environment and perishability of fruits and vegetables,a transparent packaging coating with anti-fogging and antibacterial functions,and three novel intelligent responsive antibacterial packaging materials were constructed,and explored their applications in the preservation of fruits and vegetables.The main contents of the dissertation are as follows:(1)A novel quaternary ammonium salt chitosan/polyvinyl alcohol coating with high-efficiency anti-fogging and antibacterial properties was designed for the preservation of fruits and vegetables.First,we fabricated a water-soluble quaternary ammonium salt chitosan(HACC)with excellent hygroscopicity and antibacterial properties by modifying natural chitosan with 2,3-epoxypropyltrimethylammonium chloride.HACC solution was mixed with hydrophilic film-forming agent polyvinyl alcohol(PVA)solution,and then the HACC/PVA composite coating was prepared by casting method.The prepared HACC/PVA coating could effectively prevent the fogging phenomenon caused by fruit and vegetable transpiration and reduce the decay of strawberry fruit.This coating has the advantages of good transparency,antifogging property,antibacterial activity and biocompatibility,which has potential application value in fruit and vegetable preservation.(2)A moisture-responsive nanofiber membrane was constructed for controlled release of antimicrobial agents and the preservation of fruits and vegetables.We prepared the PLA porous nanofiber membrane with ultra-high porosity by combining the "Breath Figure" principle and electrospinning technology.Thymol was loaded into the porous structure of the nanofibers by impregnation method.Finally,the pores were sealed with a hydrophilic PVA/PEG coating to obtain a moisture-responsive antibacterial packaging membrane.The results showed that humidity could trigger and control the release of thymol in porous nanofibers.In addition,the nanofiber membrane can effectively inhibit the decay of strawberry fruit.This moisture-responsive antimicrobial active packaging material can intelligently release antibacterial agents with the change of humidity in the storage environment of fruits and vegetables,thus extending the shelf life of fruits and vegetables.(3)A photo-responsive synergistic antibacterial nanofiber membrane was prepared for fruit and vegetable preservation.A metal-organic framework(MOF)material(PCN-224)was synthesized by solvothermal method using meso-tetra-(4carboxyphenyl)porphyrin(H2TCPP)as the organic ligand and zirconium(Zr)as the coordination metal.Thymol was then loaded into the porous structure of PCN224.Then,the thymol loaded PCN-224 was doped into pullulan polysaccharide/polyvinyl alcohol(PUL/PVA)nanofiber membrane by electrospinning technology to prepare antibacterial nanofiber membrane.The composite nanofiber membrane can generate singlet oxygen(1O2)under visible light irradiation due to the photosensitive properties of porphyrin molecules,and effectively inhibit the growth of Escherichia coli and Staphylococcus aureus.Furthermore,this composite nanofiber membrane could enhance the bactericidal effect through the sustained release of thymol.Fruit and vegetable preservation experiments demonstrated that this photo-responsive antibacterial nanofiber membrane loaded with thymol effectively inhibited the decay of strawberry and grape fruits through the synergistic antibacterial effect of photodynamic sterilization and thymol.(4)A pectinase-responsive nanofiber membrane was designed for controlled release of antibacterial agents and preservation of fruits and vegetables.We prepared PLA porous nano fiber by electrospinning technology and further modified with PEI to make the nanofibers surface positively charged.Then thymol(THY)was loaded into the porous structure of PLA-PEI nanofibers.Finally,the negatively charged pectin was used to block off the pores of the porous nanofibers through electrostatic adsorption to prepare pectinase-responsive antibacterial nanofiber membrane.The release of thymol is triggered by pectinase produced from pathogenic bacteria,and the in vitro antibacterial experiments showed that the nanofibers can effectively inhibit the growth of bacteria and fungi.The enzymeresponsive antibacterial nanofiber membrane could effectively inhibit the growth of Aspergillus niger through artificial inoculation of citrus.This pectinase-triggered release system can intelligently sense microorganisms on fruits and vegetables to achieve controlled and precise release of antibacterial agents.