Preparation Of Multifunctional Metal-organic Frameworks Composites And Their Applications In Food Packaging

Fresh food is easily to be oxidized and corrupted during circulation process,which leads to serious problems such as food waste and food safety issue.Thus,the presence of food packaging with antibacterial and antioxidant properties can provide an inert barrier to block external harmful factors,prevent exogenous pollution,as well as taking the initiative to protect food nutrients from deterioration and microbial contamination.Nowadays,green,low-cost and renewable bio-based packaging shows great potential to replace petroleum-based plastics in dealing with environmental pollution and alleviating energy crisis,but it still has poor mechanical properties and weak fresh-keeping effect.In particular,metal-organic frameworks（MOFs）possess lots of excellent characteristics,such as strong physicalchemical stability,good biocompatibility,diverse structures and functions,and easy modification,which can not only greatly improve the physical and chemical properties of bio-based polymers,but also provide a new strategy for food preservation with adjustable dose and controllable process.Herein,modified-MOFs composites are embedded into biopolymers as film enhancers to prepare two kinds of novel MOF-based food packaging,which mainly includes the following two aspects:1.A photo-responsive PCN@PDA/gelatin/carboxymethyl cellulose composite film（PP/GC）was prepared,which could achieve synergistic enhancement of photodynamic/photothermal antibacterial properties under single light irradiation at 660 nm（1W/cm²）,and could be further used for pork preservation.First,the effects of PDA content on the MO photodegradation and photothermal performance of PCN-224 were investigated.Then,a series of PP/GC films with the addition of PCN@PDA_1.5（the most photoactive composites）were successfully prepared by a solution-casting method.The morphology,physicochemical properties and photoactivity of the PP/GC films were optimized by adjusting the content of nanoparticles.The results showed that the 5%PP/GC film had the highest mechanical properties,water barrier and UV shielding properties,and could degrade 65.93%of methyl orange,as well as rapidly rising to 66.4℃within 60 s of irradiation.In addition,the antibacterial test indicated that 5%PP/GC film could achieve more than 99.50%inhibitory effect both on S.aureus and E.coli in 15 min,owing to the synergistic effect of reactive oxygen species and temperature rise.Finally,the results of p H value,the total number of colonies and TVB-N value of meat sample demonstrated that the pork treated with 5%PP/GC film was still in the range of sub-fresh grade during 8 days,which effectively extended the shelf life for 2～3 days.2.In order to further break through the limitations of additive and non-automatic condition-triggered sterilization effects,as well as reducing the consumption of energy equipment and human resources,a humidity-responsive LUT@ZIF-67/ethyl cellulose/zein composite film was prepared,which could timely perceive and respond to the changes of the internal moisture content with the controlled release behavior of luteolin（LUT）.The prepared film showed the antioxidant ability,antibacterial effect and the preservation of pineapple fruit cutting.Specifically,the water-sensitive ZIF-67 with higer specific surface area was selected to encapsulate the luteolin,a type of flavonoid,to prepare the LUT@ZIF-67 composite nanoparticles.The value of encapsulation efficiency and loading capacity reached the highest（98.34%and 34.09%,respectively）when the initial mass concentration of LUT was 1.0 mg/m L.It showed a water-content dependent release behavior in different concentrations of methanol-aqueous solution,indicating that humidity conditions could be used as an external stimulus to trigger LUT release.Furthermore,LUT@ZIF-67 were blended with ethyl cellulose/zein to form LZ/EZ composite film.The obtained film could effectively scavenge DPPH and ABTS⁺free radicals with releasing LUT slowly.After treatment with LZ/EZ film,the survival rates of S.aureus and E.coli at 90%RH was significantly lower than that at 50%RH.Finally,it was verified that LZ/EZ film could delay the weight loss of pineapple,reduce microbial pollution,protect color and prevent the deterioration of vitamin C.