Encapsulation Of Ethylene Into α-cyclodextrin Based Metal-organic Frameworks And Its Application

Ethylene,a natural ripening agent for fruits and vegetables,is widely used in food and agriculture.However,it is usually stored and transported in cylinders.It is exposed to risks such as leakage and explosion,and has no sustained release effect.α-CD-MOF was used as carriers to carry ethylene and study the relationship between different molecular structures and ethylene loading,reveal the adsorption mechanism of ethylene,and find the sustained release properties of ethylene in complexes and at different temperatures and relative humidity.The research results have theoretical guiding significance for the development of new ethylene carrier materials.Using α-CD as raw material,α-CD was prepared by sodium hydroxide and potassium hydroxide,respectively.The ethylene was carried by solid adsorption method.Raman spectroscopy confirmed that the presence of ethylene gas in the α-CD-MOF,and the ethylene concentrations in inclusion complexes were 47.35% and 52.91%,respectively.The release kinetics study shows that under different temperature and relative humidity conditions,the ethylene release rate increases with the increase of temperature and humidity.Avrami’s equation was used to analyze the release mechanisms from inclusion complexes,and the result showed that the ethylene release conforms to the diffusion release mechanisms in temperatures experiment,whereas the release mechanism in relative humidity experiments resembled first-order kinetics.Both metal organic frameworks have excellent ethylene loading performance,of which α-CD-MOF-K has the best controlled release characteristics and ethylene concentration.After storing at 25 °C for 30 d,only 50.13% ethylene has been released.Single crystal X-ray diffraction and molecular simulation were used to characterize the two materials.It was found that α-CD form a new porous network structure,which could effectively carry ethylene gas and slow down the release rate.In order to further study the application of the composite in the field of food industry and agriculture,α-CD,V-type starch,α-CD-MOF-Na and α-CD-MOF-K were used as solid matrix to adsorb ethylene.The solid-ethylene compounds were used in banana ripening experiments.The two groups without adding ethylene gas and injecting 1000 μL/L pure ethylene were used as control experiments.By testing the color,hardness,soluble solids content of bananas within 7 days,the ripening efficiency of the four samples is: α-CD < V-type starch < α-CD-MOF-Na ≈ α-CD-MOF-K.In the experiments of α-CD-MOF-Na,α-CD-MOF-K and 1000 μL/L pure ethylene,banana began to turn yellow on the third day and turned to full yellow on the fifth day.In the experimens of α-CD and V-type starch,the ripening efficiency was not as good as α-CD-MOF.The main factors affecting the efficiency of the ripening bananas are the ethylene concentration in the environment.High ethylene concentration accelerates banana ripening.The great ethylene loading rate and stability of α-CD-MOF make it have a good application prospect in the field of fruit and vegetable ripening.