Preparation Of Adjustable Ethylene γ-CD-MOF And Its Application In The Preservation Of Kiwi Fruit

Ethylene（C₂H₄）is a plant hormone that affects plant growth and is often used to ripen plants,including fruits,vegetables and flowers,at low temperatures.C₂H₄ is released continuously during refrigeration and transport,thus accelerating ripening.Providing the right amount of C₂H₄ at the right time also promotes the growth of fruits and vegetables and improves their flavour and colour.the production of C₂H₄ accelerates post-harvest ripening and decay of fruits and vegetables,causing significant economic losses in post-harvest storage and transport.In this study,an edible metal-organic framework（γ-CD-MOF-K）based on K⁺ions andγ-cyclodextrin（γ-CD）was prepared using ultrasonic techniques.Theγ-CD-MOF-K material was used as a carrier to adsorb C₂H₄ gas.The adsorption relationship between the MOF material and C₂H₄ gas was investigated to reveal the C₂H₄ adsorption mechanism,the adsorption performance of C₂H₄ gas inγ-CD-MOF-K and the postharvest preservation effect ofγ-CD-MOF-K on red-fleshed kiwifruit was studied.The results have great potential and theoretical guidance for the development of new C₂H₄ gas loading materials to improve the post-harvest quality of fruits.（1）The microwave-assisted loading of potassium hydroxide was used to prepare a porous metal-organic framework（γ-CD-MOF-K）usingγ-CD as the substrate,and the influence of the sonication time on the structure of the synthesized material was investigated.The XRD results showed that new characteristic peaks belonging to the MOF material appeared;FTIR results showed that the preparedγ-CD-MOF-K had characteristic peaks belonging toγ-CD,but no new characteristic peaks appeared,indicating that no new material was produced during the preparation process;TGA results showed that the thermal stability of the preparedγ-CD-MOF-K was significantly better than that of the unmodifiedγ-CD;elemental The distribution map and XPS spectrum showed that carbon（C）,oxygen（O）and potassium（K）were uniformly distributed throughout the crystal,consistent with the molecular structure,with the highest C content of 60.08%,while O and K accounted for35.01%and 4.91%,respectively.The successful synthesis ofγ-CD-MOF-K was demonstrated.（2）The Raman spectra of the synthesizedγ-CD-MOF-K showed characteristic peaks of C₂H₄ at 1577 cm^-1 and 2826 cm^-1 by solid phase adsorption with C₂H₄ gas attached,demonstrating that C₂H₄ can be stably present in theγ-CD-MOF-K material.For the loading of C₂H₄,theγ-CD-MOF-K prepared with a sonication time of 5 min had the highest loading of C₂H₄ at 56%.The results of nitrogen adsorption-desorption showed that the sample prepared by 5 min of sonication had the maximum nitrogen adsorption capacity of 260 cm²/g and the maximum BET specific surface area of 944.6 m²/g.Structural characterisation of the synthesised materials by single crystal X-ray diffraction and molecular simulation revealed that the crystallisation ofγ-CD and K⁺formed a new porous mesh structure,which was able to effectively attach C₂H₄ gas and slow down the The new porous mesh structure formed by the crystallisation ofγ-CD and K⁺was found to be effective in attaching C₂H₄ gas and slowing down the release rate of C₂H₄.（3）In order to further investigate the performance ofγ-CD-MOF-K in production practice,untreatedγ-CD,blank treatment group was used as the control group for the experiment.The unmodified treatedγ-CD,andγ-CD-MOF-K synthesized at different sonication times were placed in a confined space to adsorb C₂H₄ gas produced during the preservation of red-fleshed kiwis,and the hardness,p H,titratable acid,soluble solids,ascorbic acid and malondialdehyde of kiwis were measured over a period of 20 d.The results showed that the soluble solids（SSC）content of theγ-CD-MOF-K treatment group was approximately 14%at d 20 of storage,which was significantly higher than that of the blank treatment group and theγ-CD group.The V_C content in the control group was reduced by nearly 100 mg/100g throughout storage and theγ-CD-MOF-K treated group lost 25-50mg/100g of V_C throughout storage,which was significantly lower than the control andγ-CD groups.Theγ-CD-MOF-K synthesised by ultrasonication for 5 min had the best preservation effect.kiwifruit did not decay throughout the storage period,maintaining a good appearance and high food value,its cut surface remained in a red-centred state and internal softening was not evident.the content of C₂H₄ gas was one of the main factors affecting the accelerated ripening and decay of fruits and vegetables,and high concentrations of C₂H₄ accelerated ripening of fruits and vegetables.Therefore,the good C₂H₄ loading rate and stability ofγ-CD-MOF-K enable it to have good application prospects in the field of post-harvest preservation of fruits and vegetables.