Study On Preparation Of Cyclodextrin-based Metal-organic Frameworks And Its Application In Food Packaging Membrane

Cyclodextrin-based metal-organic frameworks(CD-MOFs)represent an environment-friendly and biocompatible class of MOFs drawing increasing attention in drug delivery.Quercetin(Que)is a kind of polyhydroxy flavone widely found in Chinese herbal medicine,which has antibacterial,anticancer,anti-inflammatory,antioxidant and free radical scavenging effects.However,due to its poor water solubility,its application in food and medicine industry is seriously restricted.In addition,with the improvement of living standards,people demand more and more food packaging materials that are safe,controllable,environmental-friendly and can prolong the storage time.Herein,in this study,CD-MOFs were prepared for loading quercetin by ultrasonic method and a new type of antioxidant membrane based on zein was developed.The entrapment efficiency and drug loading amount were analyzed by single factor experiment to optimize the loading condition.Besides,the morphological structure,functional properties and controllability ofγ-CD-MOFs before and after drug loading were systematically characterized,and the mechanism was explored.Finally,a new food packaging membrane containingγ-CD-MOFs/Que complex was developed.The main results are as follows:(1)Different kinds of CD-MOFs were synthesized by methanol vapor diffusion usingα、β、γ-cyclodextrin and through optical microscope(OM),scanning electron microscope(SEM),fourier infrared spectrum(FT-IR)and X-ray powder diffraction(PXRD),the morphology,structure and crystal properties ofγ-CD-MOFs were analyzed.SEM showed thatγ-CD-MOFs was cubic crystal with a better yield;PXRD showed thatγ-CD-MOFs has a good crystallinity.The influence of the reaction time,reaction temperature,size regulator additive amount on the morphology ofγ-CD-MOFs was analyzed and the characteristics were measured via SEM,laser confocal(CLSM),transmission electron microscopy(TEM),specific surface area and pore diameter(BET).The result was 690 m~2/g and the pores were mainly distributed during 0.9 nm and 1.7 nm.(2)The effects of ultrasonic time,ultrasonic temperature,ultrasonic power and quercetin content on entrapment efficiency and drug loading amount were measured by the single factor experiment.And then using entrapment efficiency and drug loading amount as evaluation index,the reaction conditions were optimized.The determined results showed that Que can be good loaded(33.38±0.77%,55.64±1.29 mg/g)with ultrasonic time 10 min,reaction temperature 60℃,ultrasonic power 60 W,quercetin content 20%.The structural properties,thermodynamic properties and apparent morphology ofγ-CD-MOFs/Que were confirmed via SEM,CLSM,FT-IR,PXRD,DSC.The results showed that there were no significant changes in the morphology and crystal structure because Que existed inγ-CD-MOFs in an amorphous state.FTIR showed that there wasn’t new functional group in theγ-CD-MOFs/Que after loading and the characteristic peak of Que disappeared due to the cavity of the CD-MOFs;Free radical scavenging tests and release tests ofγ-CD-MOFs/Que complex showed that the complex had antioxidant and controlled release functions.Through equation fitting of release dynamics,the release process conformed to Hugichi equation indicating the release mechanism mainly involves diffusion.Through molecular simulation to explore its mechanism,quercetin is most likely to enter the structure of dual cyclodextrin molecular pairs ofγ-CD-MOFs,with the docking free energy of-7.7kcal/mol.(4)γ-CD-MOFs/Que/Zein membrane was prepared by tape casting method using the zein as base material.The properties of membrane were examined and the results showed that with the increase ofγ-CD-MOFs/Que,the tensile strength ofγ-CD-MOFs/Que/Zein membrane decreased and the elongation at break increased.The permeability coefficient of water vapor decreased and the water resistance increased.Both antioxidant and bacteriostatic ability were enhanced.Application ofγ-CD-MOFs/Que/Zein composite membrane in litchi preservation experiment showed thatγ-CD-MOFs/Que/Zein membrane could prolong the storage period of fruits.