Journal of Bioscience and BioengineeringVOL. 111 No. 2, 232–236, 2011

www.elsevier.com/locate/jbiosc

Preparation of tea catechins using polyamide

Jian-Hui Ye,1 Liu-Xiang Wang,1 Hao Chen,1 Jun-Jie Dong,1 Jian-Liang Lu,2 Xin-Qiang Zheng,2

Ming-Yan Wu,1 and Yue-Rong Liang1,⁎

⁎ CorrespondE-mail add

1389-1723/$doi:10.1016/j

Zhejiang University Tea Research Institute, 268 Kaixuan Road, Hangzhou 310029, China1 and Key Laboratory of Horticultural Plants Growth,Development and Biotechnology, Agricultural Ministry of China, Hangzhou 310058, China2

Received 27 May 2010; accepted 30 September 2010Available online 9 November 2010

An adsorption separation method using Polyamide-6 (PA) as an adsorbent was developed to separate catechins from greentea extract. The adsorption capacity of total catechins for PA was 193.128 mg g−1 with an adsorption selectivity coefficient KA

B

of total catechins over caffeine 21.717, which was better than macroporous resin model HPD 600. The Langmuir model and thepseudo-second order mode were primely fitted to describe its equilibrium data and adsorption kinetics, respectively. PAcolumn separation by two-step elution using water and 80% (v/v) aqueous ethanol was established to prepare catechinscomplex which contained 670.808 mg g−1 total catechins and 1.828 mg g−1 caffeine. It is considered that PA was a promisingadsorbent for selective isolation of catechins.

© 2010, The Society for Biotechnology, Japan. All rights reserved.

[Key words: Camellia sinensis; Caprolactam; Caffeine-free; Two-step elution]

Tea catechins are a group of bioactive components in tea leafwhich are confirmed to have healthy benefits including antimuta-genic, anticarcinogenic, anticlastogenic and antioxidant effects (1–3),and are increasingly used as additives in the functional food stuff(4,5). The usual methods to isolate a mixture of tea catechins aremainly liquid–liquid extraction and adsorption separation. Theadvantages of liquid–liquid extraction are less energy consumptionand large capacity. However, large quantities of organic solvents suchas ethyl acetate, propyl acetate, chloroform and dichloromethane areused in liquid–liquid extraction, resulting in a trace of undesirablesolvents remained in the final products, making the food safetyproblems hang over. The adsorption separation method may beadvantageous because of its simple process and solvent control. Theadsorbents adopted in adsorption separation of tea catechins includeC-18 bonded silica and resins Amberlite XAD-7HP and AmberliteXAD-4 (6).

Polyamide (PA) contains functional groups including acylamino,terminal amino and carboxyl groups which can reversibly form stronghydrogen bonding with substrates and eluents. It is used in thechromatography of phenols and carboxylic acids (7,8). A thin layerchromatography of theaflavins on PA is reported (9). However, thereis no report on the preparative isolation of tea catechins using PA as anadsorbent. It is reported that the cyclic and linear oligomers from themanufacturer of PA have an adverse impact on the properties of finalpolymer, such as chemical resistance, thermal stability and mechan-ical intensity (10,11), indicating a pretreatment of PA is requiredbefore use.

ing author. Tel.: +86 571 86971260; fax: +86 571 86971704.ress: yrliang@zju.edu.cn (Y.-R. Liang).

- see front matter © 2010, The Society for Biotechnology, Japan. All.jbiosc.2010.09.019

In the present study, PA was used to isolate catechins from teasolution, and the adsorption characteristics, including kinetics,isotherm and column chromatography, were studied. Mixtures oftea catechins from green tea extract were prepared in a fixed bedcolumn packed with PA.

MATERIALS AND METHODS

Materials Green tea extract powder and green tea leaf used in the present studywere supplied by CinoTea CO., Ltd. (Hangzhou, China). The green tea extract powderwas prepared by extracting the green tea leaf at 90°C in water, filtering through 0.25 μmcellulose acetate ultrafiltration membrane, concentrated by reverse osmosis and finallyspray drying. The tea powder was completely dissolved in water without suspendedmatter. Polyamide-6 (PA, 0.25–0.60 mm in diameter) was purchased from Luqiao SI-JIABiochemical Plastic Company (Taizhou City, China). Chemical purity grade ethanol wasfrom Sinopharm Chemical Reagent CO., Ltd. (Beijing, China). HPLC referencecompounds of catechins and caffeine was Sigma products (Sigma-Aldrich, St. Louis,MO, USA). The other chemical reagents used were of HPLC grade (Jinmei BiotechCorporation, Tianjin, China). The water used was prepared by an EASYPure II UV-UltraPure Water System (Barnstead International, Dubuque, IA, USA).

Pretreatment of PA To remove the oligomers and ethanol-dissolved sub-stances from the PA adsorbent, 1 kg PA was drenched in 8 L 95% (v/v) ethanol on 70°Cwater bath for 40 min, decanted the ethanol and replaced with fresh ethanol as before.The PA was then washed using 8 L water for three times. The pretreated PA wasnaturally dried at room temperature.

Test of adsorption selectivity Tea solution was prepared by dissolving 13.5 ggreen tea powder in 1 L pure water. Six g of the pretreated PA was placed in 500-mLglass flasks containing 200 mL of the tea solution. The flasks were shaken at 150 rpmand 30°C for 12 h in a H2S-H water bath shaker (Donglian Electronic Technology CO.,Ltd., Harbin, China). The solution was separated from the PA by filtrating through a‘Double-Ring’™ no.101 filter paper (Xinhua Paper Co. Ltd., Hangzhou, China) andcentrifuged at 5000 × g for 25 min. The supernatant was injected into HPLC. Theadsorption capacity was calculated by the following Eq. 1:

q =V C0−Cð Þ

Gð1Þ

rights reserved.

CHRONIC FENTANYL ADMINISTRATION 233VOL. 111, 2011

where q is adsorption capacity per gram adsorbent (mg g-1), C0 and C are the initial andfinal solute concentrations of the solution (mg mL-1), respectively. V is the solutionvolume (mL) and G is the weight of adsorbent used (g).

Adsorption selectivity refers to the extent to which different adsorbates boundonto an adsorbent. Selectivity coefficient KA

B is the equilibrium constant for the reactionof displacement of one adsorbate by another adsorbate in a complex with the substrate.The tea solution contains tea catechins and caffeine. Decaffeination is necessary duringisolation of catechins complex. The KA

B was used to evaluate the selective adsorptioncapacity of PA to catechins over caffeine and was calculated by the following Eq. 2:

KBA =

RB = RA

CB = CA=

CA

CB×

RB

RAð2Þ

where KAB is selectivity coefficient in which A and B represent caffeine and total

catechins respectively. CA and CB are concentrations (mg mL−1) of caffeine and totalcatechins in the solution at equilibrium; RA and RB are adsorption capacities (mg g−1)of caffeine and total catechins in the adsorbent phase at equilibrium, respectively.

Test of adsorption kinetics Ten grams of the pretreated PA was placed in a500 mL glass flask with 360 mL of tea solution (15 g L−1) and shaken at 150 rpm inwaterbath at thermodynamic temperatures 288 K, 303 K and 318 K, respectively. Thethermodynamic temperature is calculated by +273°C. The tea solutions sampled atdifferent time intervals (0–360 min) were filtered and centrifuged as above before HPLC.

Test of adsorption isotherm PA (1.5 g) was shaken with 50 mL of tea solutionat concentrations ranging from 4.5 g L-1 to 31.5 g L−1 in H2S-H water bath shaker at150 rpm for 12 h at temperatures of 288 K, 303 K and 318 K, respectively. The solutionswere filtered and centrifuged as above before HPLC.

Gradient elution One milliliter of the tea solution (180 g L−1) was loaded onthe PA column (10 mm i.d.×120 mm). The columnwas washed with 30 mL pure waterand then eluted with 20 mL ethanol solutions at increasing concentrations (10, 20, 40,60 and 80%, v/v) at flow rate 1 mL min−1. The eluates were collected in 5 mL fractionsfor HPLC analysis.

Preparation of catechins complex from green tea leaf One kilogram of greentea leaf was extracted with 15 L pure water at 90°C for 40 min. The tea solution wasfiltered through two layers of gauze and then loaded onto a column (66 mm i.d.×550 mm) packed with PA at a flow rate 100 mL min−1. The column was rinsed with6 Lwater and sequentially eluted with 6 L of 80% (v/v) ethanol solution at 35 mLmin−1.The ethanol eluate was collected and concentrated to 1 L in an evaporator at reducedpressure and 45°C, and finally dried using an OPD-8 laboratory spray dryer (OhkawaraDryers CO., Ltd., Shanghai, China) at inlet temperature 190°C and outlet temperature105°C. The obtained tea catechins complex was kept in a desiccator containing silica gelat room temperature. The column was washed with pure water to remove ethanol, andthe adsorption process was repeated again.

The regenerationofPAcolumnwascarriedout in the fixedbedbyusing6 Lof 1 NNaOHtodrench theusedPA for12 h,washing topH7withpurewater. Then thebedwas soaked in6 L of 0.2 N HCl overnight, and finally rinsed with pure water to pH 7 for recycle test.

HPLC analysis Concentrations of catechins and caffeine were analyzed by amodified method described in previous paper (12): injection volume 10 μL,phenomenex C18 column (4.6 mm×150 mm), column temperature 28°C, mobilephase A=acetonitrile/acetic acid/water (6:1:193, v), mobile phase B=acetonitrile/acetic acid/ water(60:1:139, v), linear gradient elution: from 70%(v) A/30%(v) B to 15%(v) A / 85%(v) B during early 33 min and then 15% (v) A/85% (v) B till 38 min at flowrate 1 ml min−1, monitored by a Shimadzu SPD ultraviolet detector at 280 nm.

Data analysis All the above tests were carried out in triplicate and the meanvalues of the triplicate tests were presented.

RESULTS AND DISCUSSION

Adsorption selectivity The PA adsorption capacities were193.128 mg g−1 to total catechins and 2.189 mg g−1 to caffeine at

TABLE 1. Concentrations of tea catechins and

Samples GC EGC C EC EGCg

Tea powderb

(mg g−1) 8.444±0.074 64.815±0.963 1.778±0.074 15.111±0.222 119.333±0PA adsorptionc

(mg g−1) 3.152±0.000 16.546±0.963 0.788±0.088 4.815±0.175 127.993±0Eq Concd

(g L−1) 0.078±0.001 0.686±0.002 0.015±0.000 0.149±0.001 0.149±0Ini Conce

(g L−1) 0.114±0.001 0.875±0.013 0.024±0.001 0.204±0.003 1.611±0

a SD, standard deviation.b Tea powder used to prepare tea solution.c Adsorption capacity of PA at equilibrium.d Eq Conc, concentration at equilibrium.e Ini Conc, initial concentration.

equilibrium (Table 1), with a selectivity coefficient KAB of total

catechins over caffeine 21.717. Previous research showed that theadsorption capacities of model macroporous resin HPD 600 to totalcatechins and caffeine were 156.3 mg g−1 and 18.8 mg g−1 respec-tively, with a selectivity coefficient KA

B of 0.54 (13). Both adsorptioncapacity and selectivity coefficientKA

B at equilibrium are importantparameters to evaluate the performance of adsorbents. Here catechinsare the primary adsorbates and caffeine is the interfering adsorbate.The higher the selectivity coefficient is, the less the effect of theinterference comes from caffeine. These suggest that the PAadsorption capacity to catechins and selectivity are better thanthose of macroporous resin HPD 600, showing PA is a promisingadsorbent for separation of tea catechins from green tea.

PA, a polycondensate of caprolactam, has functional acylaminogroups which can reversibly form strong hydrogen bonding withphenolic compounds (14). Tea catechins are a group of plantpolyphenols with plentiful hydroxyl groups. For example, themolecule of (−)-epigallocatechin gallate (EGCg), the most abundantpolyphenols in tea, has eight hydroxyl groups. PA aggregatescatechins from tea solution through hydrogen bonding as shown inFig. 1. The molecular structure of caffeine without any hydroxyl groupis greatly different from that of tea catechins, and this resulted in agood adsorption selectivity of PA to total catechins. The previouslyreportedmacroporous resin HPD 600, polymerized by divinylbenzeneand with a three-dimension structure full of pores, mainly interactswith tea catechins through Van derWaals force due to its tremendoussurface area. Van der Waals force is regarded as the main action formacroporous resin to isolate natural compounds but it is a weakerinteraction between molecules than that of hydrogen bonding. As aresult, caffeine, the interfering adsorbate in the tea solution, is moreadsorbed by macroporous resin HPD 600. These explain why PA had abetter selectivity adsorption than macroporous resin HPD 600.

Adsorption kinetics Parameters of adsorption kinetics areusually used to evaluate the reaction pathways and the mechanismof adsorption reactions. The fits to the pseudo-first order and thepseudo-second order models of present data were investigated.

The pseudo-first order model of Lagergren (15) is expressed asEq. 3:

dqtdt

= k1 qe−qð Þ ð3Þ

Integrating and rearranging the Eq. 3 to a linear form as Eq. 4:

log qe−qtð Þ = log qe−k1

2:303t ð4Þ

where qe is the solute concentration in the solid phase (mg g−1) atequilibrium, qt is the solute concentration in the solid phase at anygiven time t (mg g−1) and k1 is the rate constant.

caffeine in tested samples (mean±SD)a.

GCg ECg Cg Total catechins Caffeine

.667 5.407±0.074 29.333±0.074 1.037±0.000 245.259±1.407 22.000±0.074

.875 6.041±0.088 32.830±0.088 0.963±0.000 193.128±1.596 2.189±0.088

.001 0.004±0.000 0.021±0.000 0.003±0.000 1.105±0.001 0.272±0.002

.009 0.073±0.001 0.395±0.002 0.014±0.000 3.310±0.019 0.296±0.002

FIG. 1. Scheme of hydrogen bonding interaction between PA and tea catechins.

TABLE 3. Langmuir parameters of total catechins onto PA at different temperatures a.

Temperature Langmuir

Kb qm R2

288 K 2.904 331.126 0.961303 K 2.661 326.797 0.981318 K 2.097 271.003 0.982

a Initial concentrations 2.25-31.50 g L−1.

234 YE ET AL. J. BIOSCI. BIOENG.,

The pseudo-second order model (16) was described by Eq. 5:

dqtdt

= k2 qe−qð Þ2 ð5Þ

Integrating and rearranging the Eq. 5 to a linear form as

tqt

=1

k2q2e+

1qe

t ð6Þ

where k2 (g mg−1 min−1) is the second-order rate constantdetermined from the plot of t/qt vs t. The second-order rate constantswere used to calculate the initial adsorption rate (h), given by Eq. 7:

h = k2q2e ð7Þ

The kinetic parameters of total catechins adsorbed onto PAshowed good fits to both pseudo-first order and pseudo-secondordermodels (Table 2). However, based on the correlation coefficientsR2, it was more fitted to the pseudo-second order model than thepseudo-first order model. The adsorption capacities at equilibriumcalculated by the pseudo-second order model (qe (cal)) were close tothe experimental data qe (exp) (Table 2). With an increase intemperature, the qe (cal) and qe (exp) decreased while k1, k2 and hincreased (Table 2), implying that the increase in temperatureaccelerated the adsorption process but had a negative effect onadsorption capacity.

Diffusion was assumed to be the rate- controlling step for thepseudo-first order model, while chemisorption was supposed to bethe rate-limiting step for the pseudo-second order model. Thechemisorption was the macroscopic concept of reaction relative todiffusion, involving valency forces through sharing or exchanging ofelectrons between adsorbents and adsorbates (16). The presentkinetics data weremore fitted to the pseudo-second order model than

TABLE 2. The pseudo-first order and pseudo-second order kinetic pa

Temperature Pseudo-first-order model

k1 R2 k2(min−1) (g mg·−1 min−1)

288 K 0.01004 0.982 0.00022303 K 0.01064 0.913 0.00026318 K 0.01340 0.979 0.00030

a Initial concentrations 15 g L−1. qe(exp): experimental data; qe(cal): Theoretical value wer

to the pseudo-first ordermodel, suggesting that chemisorption playeda dominant role in the adsorption process of tea catechins onto PA,accompanying physical diffusion transport phenomena experimen-tally inseparable (17). The increase in temperature accelerateschemical reaction and diffusion of tea catechins in solution, resultingin an advanced equilibrium process.

Adsorption isotherm Adsorption isotherm reveals the rela-tionship between the adsorption capacity of adsorbates and concen-tration of adsorbates in solution at a given temperature (18).Langmuir model was usually used to describe the equilibrium dataand it is expressed by Eq. 8:

1qe

=1

qmKbCe+

1qm

ð8Þ

where qe and Ce are the amount of adsorbates adsorbed by adsorbent(mg g−1) and the adsorbate concentration in solution (mg mL−1) atequilibrium respectively. Kb is the association constant and qm theadsorption capacity, which are the slope and intercept of plot of 1/qeversus 1/Ce, respectively (19).

Table 3 shows the Langmuir parameters for adsorption of totalcatechins by PA at different temperatures, with correlation coeffi-cients R2 above 0.961. Since the Langmuir isotherm is established onthe assumption that the configuration of adsorbent is homogenousand each active site on adsorbent interacts with monolayer ofadsorbate molecule. The results showed good fit to Langmuir model,indicating that prevalent surface of PA is homogeneous and theadsorption of catechins onto PA mostly occurs in a monolayer. Withan increase in temperature from 288 K to 318 K, the qm for totalcatechins decreased from 331.126 mg g−1 to 271.003 mg g−1, with adecrease in Kb from 2.904 to 2.097, suggesting high temperature wasnot propitious to the adsorption capacity.

Thermodynamic parameters Thermodynamic parameters, in-cluding standard Gibbs free energy change (ΔG0), enthalpy change(ΔH0) and entropy change (ΔS0), are usually used to describetemperature dependent adsorption properties. The ΔG0 was calcu-lated based by Eq. 9:

ΔG0 = −RT ln Kc ð9Þwhere R is the gas constant, Kc is equilibrium constant, i.e., the ratio ofadsorbate concentration on solid adsorbent phase (CBe) to adsorbateconcentration in the solution phase (CAe) at equilibrium, T is thethermodynamic temperature (20). The ΔG0 for physisorption rangesfrom −20 kJ mol−1 to 0 kJ mol−1 and for chemisorption from −80 kJmol−1 to −400 kJ mol−1 (21). The ΔG0 values in the study ranged

rameters of total catechins onto PA at different temperatures.a

Pseudo-second-order mode

h R2 qe(exp) qe(cal)(mg g−1·min−1) (mg g−1) (mg g−1)

10.902 0.995 221.163 224.21512.498 0.999 213.966 219.78012.593 0.996 204.058 205.761

e calculated by Eq. 6.

TABLE 4. Equilibrium constant (KC) and Gibbs free energy change (ΔG0) of totalcatechins onto PA.

288 K 303 K 318 K

KC 1210.384 636.871 305.897ΔG0(kJ mol−1) −16.998 −16.226 −15.132

FIG. 2. Van't Hoff plot for the adsorption of total catechins onto PA.

CHRONIC FENTANYL ADMINISTRATION 235VOL. 111, 2011

from−16.998 kJ mol−1 to−15.132 kJmol−1 (Table 4), suggesting theadsorption processes is spontaneous physisorption.

Enthalpy change (ΔH0) and entropy change (ΔS0) were calculatedfrom Kc through Van't Hoff Eq. 10:

ln Kc =ΔS0

R−ΔH0

RTð10Þ

Enthalpy change (ΔH0) is the amount of heat released or absorbedas the reaction occurs at constant pressure. Entropy change (ΔS0) is a

FIG. 3. Chromatogram of catechins and caffeine on PA with aqueous ethanol by gradient elutiaqueous ethanol of increasing concentrations. The part marked by different alphabetic let(30 ml); B=10%(20 ml); C=20%(20 ml); D=40%(20 ml); E=60%(20 ml); F=80%(20 ml)

measure of freedom degree for the adsorbed species or the disorder ofa system. The ΔH0 and ΔS0 which were obtained from the slope andintercept of the Van't Hoff plot of lnKc vs 1/T (Fig. 2) were−34.846 kJmol−1 and −61.760 J mol−1 K−1 respectively. The negative value ofΔH0 indicates that the adsorption of catechins onto PA wasexothermic. Therefore, the adsorption equilibrium moved towardadverse orientation as the temperature rose. These are the reasonsthat a reduction in the adsorption capacity of total catechins occurredwith the increase in temperature (Tables 2 and 3). The ΔH0 for Vander Waals force ranges from −10 kJ mol−1 to −4 kJ mol−1, forhydrogen bonding from −40 kJ mol−1 to −2 kJ mol−1 and forchemical bonding below−60 kJ mol−1 (22). TheΔH0 value calculatedby Eq. 10 in the present study was −34.846 kJ mol−1, suggestinghydrogen bonding is the predominant interaction between teacatechins and PA. The ΔS0 calculated by Eq. 10 in the present studywas −61.760 J mol−1 K−1, indicating that the uniformity of theadsorption system is increased, which is in accordance with themonolayer adsorption of catechins onto PA inferred above.

Gradient elution Ethanol, a kind of non-toxic and efficientorganic solvent weakens the hydrogen bonding between adsorbatesand adsorbents and increases the solubility of adsorbates. Aqueousethanol is generally used as an eluent in the isolation of naturalcompounds. Fig. 3 showed the chromatogram of catechins andcaffeine (CAFF) eluted from PA column by gradient aqueous ethanol.Caffeine was eluted by water (Fig. 3A). Catechins were graduallyeluted with an increase in ethanol concentration up to 60% (v/v).(−)-Epigallocatechin gallate (EGCg) was partially eluted by 80% (v/v)ethanol. The results suggest that caffeine is perfectly separated fromtea catechins during the gradient elution. This implies that two-stepelution might be a good process to prepare caffeine-free catechins, i.e.using water to remove caffeine and then 80% (v/v) aqueous ethanol toelute catechins.

Preparation of catechins complex from tea leaf Tea leaf extractwas loaded onto the PA column and eluted sequentially using water andthen 80% (v/v) ethanol. A complex powder of tea catechinswas obtainedas the ethanol phase was concentrated and spray dried. The yield ofcatechins complex ranged from 39.4 g to 42.8 g per kilogram tea leaf(Table 5). Composition of the catechins changed with the sorption–desorption cycles (Table 5). Total catechins level was 670.808 mg g−1 in

on. Column, 10 mm i.d.×120 mm flow rate, 1 ml/min. The adsorbates were eluted withters represented ethanol solution of various concentrations(v/v), respectively: A=0.

TABLE 5. Chemical compositions of used tea leaves and catechins complex prepared by PA and regenerated PA columns (mean±SD, mg g−1)a.

Sample Weight(g)

GC EGC C EC EGCg GCg ECg Cg Total catechins Caffeine

TLb 1000.0 17.521±0.682 53.010±0.952 7.913±0.091 7.914±0.097 57.183±0.125 21.264±0.153 12.582±0.077 6.318±0.203 183.705±1.598 49.532±0.022Ac 42.8±1.5 47.133±0.815 83.921±1.988 39.426±0.592 35.927±0.593 244.012±3.137 131.222±1.646 58.012±0.719 31.155±0.456 670.808±5.742 1.828±0.337Bd 39.4±1.0 46.412±0.932 83.637±2.103 35.711±0.679 33.847±0.475 238.676±3.431 123.934±1.593 55.472±0.812 30.234±0.348 647.923±5.541 13.388±0.563Ce 42.3±1.1 49.215±0.973 84.527±2.159 36.420±0.443 35.228±0.731 242.738±2.912 127.926±1.727 56.614±0.629 34.911±0.328 667.579±4.330 2.117±0.401

a SD, standard deviation.b TL, tea leaves used to prepare tea catechins complex.c A, catechins complex powder prepared from the 1st sorption–desorption cycle.d B, tea catechins complex powder prepared from the 2nd sorption–desorption cycle.e C, tea catechins complex powder prepared by regenerated PA column.

236 YE ET AL. J. BIOSCI. BIOENG.,

the first sorption–desorption cycle, with a caffeine level of 1.828 mg g−1.Caffeine level was significantly increased in product obtained from thesecond sorption–desorption cycle. However, the product isolated fromthe regenerated column after two sorption–desorption cycles had asimilar concentration of caffeine with that of the first cycle (Table 5).These suggest that column regeneration should be carried out after eachsorption–desorption cycle. The yield of catechins complex varied withthe sorption–desorption cycle and it was increased by columnregeneration (Table 5).

PA showed substantial advantages for preparing tea catechinscompared to the reported results (13,23). The adsorption capacity ofcatechins for PA was higher than those of macroporous resin HPD 600(13) and ion exchange fiber (23). The ratio of catechins to caffeine inthe product of present study was higher than that prepared bymacroporous resin HPD 600 (13), suggesting that PA had a betterselectivity adsorption to catechins than the later. It is considered thatPA is an ideal adsorbent for preparing catechins from tea solution. Theadsorption process of catechins onto PA was an exothermic onemostly occurred in a monolayer, during which physisorption takeplace spontaneously with hydrogen bonding as the predominantinteraction between tea catechins and PA. Caffeine in tea extractloaded onto PA column can be mostly removed by washing withwater and catechins complex with low caffeine level can be obtainedby elution with 80% (v/v) aqueous ethanol. The sorption–desorptioncycle had great influence on the caffeine concentration of product andregeneration is necessary after each sorption–desorption cycle.

ACKNOWLEDGMENTS

This workwas financially supported by the Agricultural Ministry ofChina (Project No. nyhyzx 2007-03-35-1).

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