Extraction And Purification Of Natural Antioxidants Based On Cloud Point Separation System

With further understanding of antioxidants,synthetic antioxidants were gradually discarded due to their potential hazards to human health.In recent years,more and more researchers have devoted themselves to studying how to separate and purify natural antioxidants efficiently.However,most natural antioxidants were found in fruits,vegetables,or Chinese herbal medicines with complex ingredients and low content of effective active substance,which brought some difficulties in separation of natural antioxidants.As a new type of separation and enrichment technology,cloud point separation has the advantages of simple operation,good biocompatibility,high concentration rate and low price,which attracted many researchers’attention.However,for complex matrices,cloud point separation can only enrich and initially separate primary substances and cannot selectively separate specific products.This limits the practical application of cloud point separation.Therefore,the study of cloud point separation combined with other methods to improve the specificity of its separation has aroused great interest of researchers.This paper has focused on establishing a new system aimed for improving the specificity of cloud point separation to obtain natural antioxidant samples with higher purity by combining cloud point separation with solid phase adsorption or liquid-liquid extraction.The specific research content includes the following three aspect:（1）Chitosan/hydroxyapatite（CS/HAP）was synthesized by hydrothermal method and modified with 4-carboxyphenylboronic acid（CPBA）to obtain 4-carboxyphenylboronic acid-chitosan/hydroxyapatite agent（CPBA-CS/HAP）,which was used for the specific adsorption of vitamin B₁₂.The adsorption efficiency of different absorbents on vitamin B₁₂ was compared through experimental data,In addition,the influence of different adsorption materials,substrate concentration,adsorption time and influence of p H on the adsorption efficiency were explored.The adsorption kinetics and isothermal adsorption kinetics were studied.Then the vitamin B₁₂on CPBA-CS/HAP was desorbed by surfactant,and the cloud point separation was performed to further purify the vitamin B₁₂ by removing excess surfactant in the solution and residual impurities in the adsorption process.Finally,the comparatively purer vitamin B₁₂was obtained by combining the crystallization method with a purity of 92.63%.（2）The zinc-tin layered double hydroxide（Zn-Sn LDH）was synthesized by hydrothermal method,and the metal-organic framework material（Zn-MOF）of zinc-carboxyl ligand with mixed ligands was grown in situ on the surface.The layered double hydroxide-metal organic framework composite（LDH/MOF）was used for the specific adsorption of vitamin B₂.The experimental data was used to compare the adsorption efficiency of different adsorbents for vitamin B₂.Otherwise,the effect of concentration,adsorption time and influence of p H on the adsorption efficiency were explored.To study the adsorption kinetics and wasothermal adsorption kinetics,the vitamin B₂ on the LDH/MOF was desorbed by surfactants and the cloud point was separated to further purify the vitamin B₂,by combining the method of crystallization to obtain a relatively pure product of the vitamin B₂ with a purity of 93.92%.（3）Ultrasound-assisted eutectic solvents（DESs）were used to extract baicalin in Scutellaria baicalensis Georgi,and the effects of different types of DESs,material-to-liquid ratio,water content of DESs,ultrasonic time and ultrasonic temperature on the extraction efficiency were studied.Afterthat,using surfactants to separate the cloud point of baicalin in the solution,the effects of surfactant concentration and equilibrium temperature on the recovery rate were studied.Back-extracted with Na OH solution have been utilized after finishing the cloud point separation,and a relatively pure product of baicalin was obtained by the method of acid precipitation with a purity of 89.72%at last.