| Tea polyphenols,one of the main bioactive components in green tea,are widely used in the area of food industry and medicine because of their high potential of oxidation resistance,blood pressure declination,radiation resistance and cancer prevention.The level of caffeine in tea polyphenols extracts,which reaches to 2%～10%by weight,is usually much higher than that in commercial tea.Excessive intake of caffeine exerts adverse effects,including sleep deprivation,abortions and miscarriages,psychosocial stress and hypersensitivity.Caffeine should be removed from tea extracts before it is applied to preparation of foods or drugs.In order to obtain caffeine-free tea extracts,attempts have been made including organic solvents extracting and removing caffeine,metal ions precipitation tea polyphenols and column chromatography separation.Column chromatography separation is used more widely than other methods.Macroporous resin is a kind of popular adsorbents for column chromatography separation.However,resin cannot remove caffeine thoroughly from tea extracts because of its poor selection capability.Catechins with abundant hydroxyls has high potential of hydrogen bond formation.Monomers with high binding capacity of hydrogen bond,such as methyl methacrylate,were used for preparing the polymers.The characteristics and adsorption capabilities of these polymers were studied by static adsorption and column chromatography,focusing on the study of adsorption isotherm equation, characteristics of kinetics and elution condition.The results showed that polymers preparation optimized as mixing monomers such as acrylamide(AM),methacrylic acid(MAA)and methyl methacrylate(MMA), crosslinkers(ethylene glycol dimethacrylate)and initiator(azobisisbutyronitrile),and incubating at 60℃for 24 h in acetonitrile solution.Static adsorption results showed that absorption capacity for catechins by polymers was much higher than for caffeine,i.e.polymers could absorbed catechins selectively. The kinetic curves studies showed that equilibrium time for caffeine adsorption on the MAA and AM polymers was 50 min,while the time of catechins was 100 min. On the MMA polymers,the equilibrium time for adsorption of caffeine and catechins was 30 min and 270 min,respectively.The adsorption capacities for catechins reached to 105 mg·g-1～120 mg·g-1,was higher than that for caffeine(10 mg·g-1～15 mg·g-1). Therefore,polymers,prepared from monomer of MAA,AM and MMA,were proved to be effective adsorbents for decaffeination of tea extracts.The pseudo-second order model were used to describe the adsorption kinetic. The adsorption capacity(qe)calculated by model was consisted with the experimental qe with error less than 5%at 25℃for the three polymers.Langmiur isotherm equation could be used for describing catechins and caffeine adsorption behavior on the three polymers.Saturated adsorption capacity of catechins at 15℃was higher than that at 25℃and 35℃.Therefore,low temperature was benefited for decaffeination treatment from tea extracts.Column chromatograph separation using MAA,AM and MMA polymers as bed absorbents investigation showed that the breakthrough point of caffeine was much earlier than that of catechins,and especially the point of non-gallated catechins was earlier than that of gallated catechins.It was suggested that the adsorption amount of catechins by polymers was much higher than that of caffeine.Tea extracts was loaded on the polymer columns and washed sequentially with aqueous ethanol of increasing concentrations.The results showed that caffeine could be easily eluted by 20%～30%aqueous ethanol,while for elution the catechins much high concentration aqueous ethanol such as 40%～80%should be loaded.In order to save the elution time,30%aqueous ethanol was selected to remove caffeine,and 60%～80%ethanol was used for eluting catechins.Regenerated polymers by ethanol elution were used for reloading examination. The results showed that the breakthrough point of caffeine on the regenerated polymers column bed was earlier than that on the fresh polymers column,and that little effect of regeneration on breakthrough point of catechins was also found.It was suggested that polymers was suitable for regeneration and reutilization. In conclusion,polymers,prepared from monomers of MAA,AM and MMA, were promising absorption materials for decaffeination of tea catechins.
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