| The optimization of extraction conditions of polyphenols from puer tea were studied inthis paper. At the same time, the resin adsorption method was adopted to take off the caffeine,and the best flow rate, pH, elution agents, etc. were studied. Besides, the thermodynamics andkinetics characteristics of the resin were used to analyze the resin adsorption process. Inaddition, compared with the Vc, the antioxidant activities of polyphenols in decaffeinated teawere evaluated by using4indexes.The726A puer tea was chosen as the sample, and water as the extraction solvent todetermine the best extraction conditions of puer tea by using an orthogonal array design. Thebest extraction conditions of caffeine were100℃, solid-liquid ratios1:45,60min; as to thepolyphenols,100℃, solid-liquid ratios1:35, and extraction time30min were the bestconditions. Comparing different tea samples produced by different factories, the old teaproduced by Tiandiren Tea Limited Corporation in Menghai County is the best one whoseextraction rate of polyphenols was9.21%, and caffeine2.13%.Adsorption rate of caffeine and polyphenols were used as indexes to select the best resinwhich turned out to be the AL-1from ten kinds of different resins (AB-8, NKA-9,001*7, D61,HPD-400, HPD-722, HPD-750, AL-1, AL-2, OU-2). The optimized condition for isolationand purification of caffeine was0.75mL/min adsorbing flow rate, and pH of the sample was5.2, the eluent was100mL of50%ethanol. The caffeine was eluted down after the outflowsreached40mL, while polyphenols were eluted completely before the outflows reached45mL.According to their elution sequences, collecting effluent liquids in different time slots can beconsidered to separate caffeine and polyphenols effectively.The dynamics and thermodynamics model of adsorption process showed that theadsorption process of AL-1can fit the Level1Lagergren equation (R~2=0.960) and the level1dynamic model well. At the same time, results showed that the rate controlling step in theadsorption process was mainly liquid membrane diffusion, and the intragranular diffusion alsohave certain effect on the adsorption of caffeine. The Langmuir and Freundlich isothermaladsorption equations were used to fit the adsorption process, the result showed that theFreundlich isothermal adsorption equation can describe the process better (R~2>0.990), and thecaffeine adsorption of AL-1was the preferential adsorption. The enthalpy change ofadsorption ΔH≥0showed that the adsorption process of AL-1was endothermic process, raising temperature was beneficial to adsorption. The free energy of adsorption ΔG showedthat it was a spontaneous physical adsorption process. Besides, the entropy change of thesystem showed that the adsorption of caffeine was promoted by entropy.The DPPH radical scavenging activity, H2O2scavenging activity, reducing power andinhibition of soya bean lecithin peroxidation assays were used to detect the antioxidantactivities of decaffeinated teas in vitro. Results showed that both the original tea anddecaffeinated tea have evident antioxidant activities. When the concentration was10μg/mL,their DPPH radical scavenging activities were respectively90.54%and88.59%. The H2O2scavenging activity assay showed that when the concentration of the sample reached100μg/mL, their scavenging activities were75.04%and68.67%. The reducing power assayshowed that both of them have good reducing power, and their activities present a good linearrelationship with their concentrations. When the concentration were80μg/mL, theperoxidation inhibition activities were11.53%and9.37%respectively. When theconcentrations were low, the peroxidation inhibition ratios of teas and Vc were all low. |
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