Kinetics Of Graphene Oxide-assisted Extraction Of Bamboo Leaves Flavonoids And Separation And Purification Of Extraction Solution

Bamboo leaves flavonoids(BLF)have multiple functions such as anti-oxidation,bacteriostasis,liver protection and anti-radiation effects.Firstly,the first-order kinetic model,the slab model of Fick's second law,the second-order kinetic model and the two-stage washing/diffusion model were used to simulate the experimental data of graphene oxide(GO)-assisted ethanol reflux extraction(GERE)and ethanol reflux extraction(ERE)extraction process.It was found that the two-stage washing/diffusion model can describe the extraction process of BLF by GERE and ERE very well.Secondly,the influences of stirred speed,ethanol concentration,extraction temperature,liquid to solid ratio and GO dosage on the extraction process of BLF were examined.The result showed that stirred speed had little effect on the extraction rate,the external diffusion resistance could be ignored and the extraction rate was mainly controlled by the inner diffusion process.The relationship of the apparent diffusion constant Dd1' of fast diffusion stage with the extraction temperature was deduced.For ERE,In Dd1'= 5.8302-1925.6/T and the activation energy is 16.01 kJ·mol-1.For GERE,when GO dosage was 15 mg/g dry bamboo leaves,In Dd1'=3.098-948.33/T,the activation energy is 7.88 kJ·mol-1,which is 50.78%lower than that for ERE.Thermodynamics results revealed that the extraction of BLF was an endothermic,entropy increase process,which could be carried out spontaneously.The addition of GO could increase the yield of BLF,decrease the activation energy of extraction process,and increase the extraction rate of fast and slow diffusion process.Then,the flocculation conditions of gelatin and chitosan were optimized by single factor and orthogonal experiments.Zeta potential and Fourier Transform Infrared(FTIR)spectra were used to study the flocculant mechanism.The result showed that the clarification effect of chitosan was superior to that of gelatin.And the optimum process conditions of chitosan were pH 5.5,ratio of chitosan to bamboo leaves extraction solution 0.1(mg/mL),flocculating 10min at 40 ?,and clarification time 2h.Under this condition,flavonoids retention rate and clarification rate were achieved 95.3%and 95.8%,respectively.Clarification rate of chitosan on the ethanol aqueous solution of bamboo leaves was the highest,followed by the water-extraction solution,and clarification rate on the ethanol and GO-ethanol extraction solution were lower.There was no significant difference in flavonoids retention rate,when chitosan was used to flocculate the extraction solution of four extraction processes,all of the flavonoids retention rate were more than 95%.Zeta potential and FTIR spectra results revealed that chitosan could remove lipids,tannins,proteins,polysaccharides and small molecular terpenoids in bamboo leaves extraction solution by electrical reaction and adsorption bridging to improve the clarity.