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Research / AratrmaGIDA (2010) 35 (3): 161-168

POLYPHENOLS, ALKALOIDS AND ANTIOXIDANTACTIVITY OF DIFFERENT GRADES TURKISH BLACK TEA

Nihal Turkmen Erol1, Ferda Sar2, Y. Sedat Velioglu*2

1 Uludag University, Vocational School of Technical Sciences, Bursa2 Ankara University, Faculty of Engineering, Department of Food Engineering, Ankara.

Received /Geli tarihi: 14.05.2009Received in revised form /Dzeltilerek geli tarihi: 29.09.2009

Accepted /Kabul tarihi: 20.10.2009

Abstracte content of polyphenols and alkaloids of seven grades Turkish black tea was investigated as well astheir antioxidant activity. Polyphenol and alkaloid contents of teas were determined using HPLC method.Antioxidant activity was evaluated by DPPH radical assay. In tea samples examined, two alkaloids (caeineand theobromine), two avan-3-ols (EGCG and ECG), three avonol glycosides (Q3RG, Q3G and K3RG)and four individual theaavins (TF-f, TF-3-G, TF-3-G and TF-3,3-DG) were identied and quantied.Signicant dierences were detected in biochemicals content and antioxidant activity between dierentgrades black teas. In general, the contents of alkaloids, Q3RG, Q3G and theaavins in 1st, 2nd, 3rd and 7th

grade teas and the contents of avan-3-ols in 4th, 5th and 6th grade teas were found to be higher. However,there was no signicant dierence in K3RG content of the teas. 1 st, 2nd, 3rd and 7th grade teas showed also

higher antioxidant activity.

Keywords: Black tea, alkaloid, phenolics, tea grade, antioxidant activity

FARKLI SINIF TRK SYAH AYLARININ POLFENOL VEALKALOD ERKLER LE ANTOKSDAN AKTVTES

zetBu almada yedi farkl snf Trk siyah aynn polifenol ve alkaloid ierikleri HPLC yntemiyle, antioksidanaktiviteleri ise DPPH radikal yntemiyle aratrlmtr. ay rneklerinde iki alkaloid (kafein ve teobromin),

iki avan-3-ol (EGCG ve ECG), avonol glikoziti (Q3RG, Q3G and K3RG) ve drt teaavin bileii (TF-f, TF-3-G, TF-3-G and TF-3,3-DG) tanmlanm ve miktarlar belirlenmitir. Farkl snf aylarn yapsndabulunan bileiklerin miktarlarnn ve bunlarn antioksidan aktivitelerinin istatistik olarak anlaml dzeydefarkl olduu ortaya konulmutur. Genel olarak aylarda bulunan alkaloidlerin, Q3RG, Q3G ve teaavinlerile antioksidatif aktivitenin 1., 2. 3. ve 7. snf aylarda, buna karn avan-3-ollerin ise 4., 5. ve 6. snfaylarda daha yksek olduu saptanmtr. K3RG asndan ay snar arasnda farkllk grlmemitir.

Anahtar kelimeler: Siyah ay, alkaloid, fenolik bileik, ay snf, antioksidan aktivite

* Corresponding author/ Yazmalardan sorumlu yazar ;

- velioglu@eng.ankara.edu.tr,& (+90) 312 596 1166,7 (+90) 312 317 8711

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INTRODUCTION

Black tea is the most widely consumed in Turkeywhich is the sixth largest producer of black tea af-ter China, India, Sri Lanka, Kenya and Indonesia inworld tea production (1). In tea trade, the marketvalue depends mainly on the quality of the brewedliquor and the texture or appearance of the madetea (2). In black tea, during the fermentation proc-ess most of catechins forming main avanols ofgreen tea are oxidized and polymerized to theaa-vins (TF) and thearubigins (TR) (3, 4) which are re-sponsible for the colour, avour and brightness oftea (5). e content of individual TF showed a sig-nicant correlation with tea taster scores and value

(6, 7). Flavonols, present as glycosides, are the oth-er important groups of polyphenols in tea (8) andblack tea contains mainly quercetin, kaempferoland myricetin glycosides (9) which contribute totea antioxidant activity (10). Caeine, theophyllineand theobromine are the main tea alkaloids andalso important factors in determining the qualityof black tea (3, 11). Caeine is the most abundantalkaloid, responsible for the briskness of tea (12).

It is well known that green tea catechins have mostof health eects. Black tea TFs, oxidation products

of catechins, also possess strong antioxidant activ-ity (13) and are considered to be much eectivecomponents for the inhibition of carcinogenesis(14). Stewart et al. (15) found that TF retained anti-oxidant capacity similar to that of (-) epicatechin(EC) monomers. Conversion of catechins to TFduring tea fermentation does not signicanty alterits free-radical scavenging activity (16).

e levels of individual and total TF of black teahave showed dierences depending on the variousfactors such as plucking season of tea shoots (17)and analytical method (18, 19). On the other hand,in the literature no information is available on theeects of tea grades on the levels of polyphenoland alkaloid of black tea. erefore, in this study,it is aimed to investigate not only the content ofpolyphenols and alkaloids but also the antioxidantactivity of seven dierent grades Turkish black tea.

MATERIAL AND METHODS

Plant materials and chemicals

Seven grades (1-7.) black teasamples were collect-ed in triplicate from a tea processing factory in the

Eastern Black Sea region. Tea grading was made byusing Middleton sieving system which can be t-ted with 5 to 10 trays, and the aperture size of the

sieves varies from 8 mesh (2.36 mm) to 40 mesh(0.425 mm). Here, ve sieve sizes were used withaperture sizes of 8 (largest), 10 (2.0 mm), 12 (1.7mm), 20 (0.85 mm), and 30 (0.6 mm) mesh. Blackteas retained by the 10, 12, and 20 mesh sieveswere separated as tea grades 1, 2, and 3, respective-ly. ese teas do not contain any broken parts. Teaspassing through the 30 mesh sieve are designatedas grade 7 or dust-tea. e largest particles of blacktea remaining over the 8 mesh sieve were passedthrough the breaker crushers and screened again

in the same system. Black teas then remaining overthe 10, 12, 20, and 30 mesh sieves were classiedas grades 4, 5, 6, and 7, respectively. Depending onprocessing technique and plucking season the ap-proximate percent distrubution of 1st to 7th gradesof teas, respectively, were as follows: 2.5; 24; 8.5; 4;50; 8 and 3. Tea samples were produced by Ortho-dox + Rotorvane + Orthodox (called as Cay-Kur)method (20).

(+)-Catechin(C), (-)-epicatechin (EC), (-)-epigallocatechin

(EGC), (-) epigallocatechingallate (EGCG), (-)-epicatechingallate (ECG), (-)-catechingallate(CG),(+)-gallocatechin (GC) and tea extract containingfree theaavin (TF-f), theaavin-3-gallate (TF3G),theaavin-3-gallate (TF3G), theaavin-3,3-digallate(TF3,3DG) were purchased from Sigma (St, Louis,Mo. USA). Caeine, theobromine, quercetin-3-glucoside (Q3G), orthophosphoric acid, HPLC oranalytical grade acetonitrile and methanol werepurchased from Fluka-Riedel-de Han (BioChemicaFluka Cheme GmbH Buchs-Switzerland).

Kaempferol-3-rhamnosylglucoside (K3RG) wasfrom Chromadex (Santa Ana, ABD). Quercetin-3-rhamnosylglucoside (Q3RG) was from Wako (PureChem. Co., Osaka-Japan).

Extraction of tea polyphenols and alkaloids

Ground tea sample (0.2 g) was extracted with 10ml 80% methanol for 14 h on a horizontal shakerin the dark. e mixture was centrifuged at 14000

g for 10 min. e supernatant was transferred intoan screw-capped amber glass vial and stored at -20C until analyzed.

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Analytical determinations

Content of tea biochemicals was determined bythe method described by Turkmen and Velioglu(21). Chromatographic peaks in the samples wereidentied by comparing their retention times andUV spectra with those of their reference standardsand by co-chromatography with added standards.Quantication was performed from the peak areaof each component and its corresponding calibra-tion curve.

Preparation of standard solutions

Stock standard solutions were prepared dissolv-ing in 80% methanol except for theobromine, dis-solved in distilled hot water, to a concentration of0.5-1 g/l and kept protected from light at -20 C forup to 2 months. Each stock solution was then usedfor the preparation of the diluted solutions (0.25-250 mg/L) for the calibration curves. Workingstandard solutions were injected into HPLC andpeak areas were obtained. Calibration curves wereprepared by plotting concentration versus area.

Antioxidant activity

e antioxidant activity of tea samples was meas-ured by using the DPPH assay (22, 23) with somemodications. 50 ml of test sample diluted for f-teenth fold was mixed with an aliquot of 1950 ml of6x10-5 M DPPH radical in methanol. e reactionmixture was vortex mixed and let to stand at 25 Cin the dark for 60 min. e decrease in the absorb-ance at 517 nm was determined using a spectro-photometer using methanol as blank. e antioxi-dant activity (AA %) was calculated according tothe following equation (I):

(I)

where Acontrol

is the absorbance of the DPPH solu-tion without sample and A

sampleis the absorbance

absorbance of the test sample.

Standard curve of reference antioxidant ascorbicacid (0-150 mg/ml) was assayed under identical

conditions for anity to scavenge DPPH. Antioxi-dant activity of samples was transformed to ascor-bic acid equivalent (AEAA) dened as g of ascorbic

acid equivalents per 100 g tea. Greater values of theAEAA are related to greater antioxidant activity ofthe sample.

Statistical analysis

All data were expressed as means standard de-viation of triplicate measurements and analyzed bySPSS for Windows (ver.10.1). One-way analysis ofvariance (ANOVA) and Duncans multiple rangetest were carried out to test any signicant dier-ences among dierent tea grades. Values ofP

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of previous studies (24-27). However, Wang et al.(27)found lower EGCG contents in Keemun andSri Lanka black teas, 0.95 (0.48) and 1.16 (0.58)

mg/100 ml (mg/g DW), respectively, which couldbe due to dierences in quality of fresh tea leaves,tea processing and analytical methods used.

e levels of ECG ranged from 0.73 mg/g DWin 7th grade tea to 2.54 mg/g DW in 6th grade tea(Table 1), which is in agreement with the study bySharma et al. (3) who reported the amount of ECGto be 1.0 ve 1.5 mg/g in orthodox and CTC blackteas extracted with 70% methanol, respectively. Onthe other hand, Nishitani and Sagesaka (28) foundacetonitrile (50%) extracts from black tea to con-

tain 18 mg/gof ECG, higher than our results. edierence can be due to the same reasons men-tioned above for EGCG. e levels of EGCG werehigher than those of ECG. Similarly, in literature,the most abundant avan-3-ol in black teas whichwere extracted with dierent solvents such as 40%ethanol, 80% methanol and water was reported tobe EGCG (4, 18, 29, 30, 31). With respect to teagrade, the higher amount of avan-3-ols was foundin 4th , 5th and 6th grade teas, followed by 1st, 2nd and3rd ones which are produced from young tea leaveswhile 4th , 5th and 6th grade teas are from old ones.is can be attributed to variation in polyphenoloxidase (PPO) enzyme activity of tea leaf compo-nents (33). Because, old tea leaves contain loweravan-3-ols and PPO activity which catalyses theoxidation of the avan-3-ols and leads to the for-mation of black tea pigments, namely, TF and TRcompared to young ones (2, 17, 20, 34). 7th gradetea which consists of combination of all other teas

contained lowest level of avan-3-ols. Informationabout polyphenols in dierent tea grades black teain the literature is lacking. erefore, we are unable

to compare our results.Concerning the avonol glycosides, the content oftotal avonol glycosides of teas ranged from 3.04mg/g DW in 5th grade tea to 3.62 mg/g DW in 7th

grade tea (Table 1). In all cases, Q3RG was the mostabundant avonol glycoside, followed by K3RG andQ3G, respectively. Similar results were reportedby previous studies (5, 15). However, in the studyof Rechner et al. (30), among avonol glycosidesof dierent brands of black teas Q3RG, Q3G andK3RG were included in the rst three order and

ranking of their amounts varied with dierent teabrand. Luximon-Ramma et al. (35) noted that inaqueous methanol extracts of nine dierent brandsMauritius black teas, as aglycones, more quercetin(1.07-3.29 mg/g DW) and lower kaempferol (0.27-0.70 mg/g DW) were determined, which supportspartly our results. While signicant dierence wasdetected in Q3RG and Q3G contents of teas, butnot in K3RG contents. In general, 1st, 2nd, 3rd and 7th

grade teas contained signicantly higher contentsof Q3RG and Q3G than 4th, 5th and 6th ones, which

may be because of the fact that young tea leavescontain higher polyphenol content (16).

In tea samples, the content of total TF compoundsvaried from 14.18 to 19.95 mg/g DW (Table 2). Inliterature, total TF contents were reported to be10.70 mg/gin Ceylon tea (14), average 8.54 mg/g

in Chinese teas (24) and 3.5711.57 mg/g in dier-ent black teas (36). ese values were lower than

Table1. Flavan-3-ols and flavonol glycosides in different grades black tea (mg/g dry weight)

Teagrade

EGCG ECG Q3RG Q3G K3RG Total flavonolglycosides

1 1.180.04a 0.940.07ab 1.750.08ab 0.520.02cd 1.100.03a 3.380.10

2 1.570.27ab 1.260.13bc 1.740.05ab 0.520.01cd 1.080.03a 3.350.10

3 2.050.20bc 1.470.14cd 1.820.07bc 0.550.01d 1.080.02a 3.450.10

4 2.380.22cd 1.900.09de 1.630.08ab 0.450.02ab 1.080.02a 3.160.11

5 3.000.30e 2.180.24ef 1.530.10a 0.440.01a 1.060.02a 3.040.13

6 3.160.40e 2.540.22f 1.630.05ab 0.480.04abc 1.050.03a 3.160.10

7 1.060.12a 0.730.07a 2.010.04c 0.510.00bcd 1.090.01a 3.620.04

Means sharing different letter (a-f) in the same column are significantly different (P

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our results, which may be due to variation in teavariety, tea processing method and extraction andanalytical methods used. In all teas, TF-3,3-DG

was the most abundant TF, followed by TF-3-G,TF-f and TF-3-G in decreasing order, which is inagreement with the results of Can et al. (17). Onthe contrary, Liang et al. (24) reported that in dif-ferent teas extracted with water, the order of TFcontents was as follows: TF-3-G (2.98 mg/g)> TF-f(2.35 mg/g)> TF-3,3-DG (2.33 mg/g) and TF-3-G(0.89 mg/g) respectively. Other studies also report-ed that dierent black teas extracted with waterhad lower TF contents and in tea samples, dier-ent TF compound was dominant depending on thetea type (37, 38). ere was signicant dierencein total TF contents between dierent grades teas.1st, 2nd, 3rd and 7th grade teas contained higher con-tents of total TF compared to 4th, 5th and 6th ones asobserved for avonol glycoside. is can be attrib-uted to the higher avan-3-ols content and PPOactivity in young tea leaves which form more TF asa result of oxidation.

Caeine and theobromine in teas were in the rangeof 23.16- 26.26 mg/g DW and 0.18- 0.20 mg/g DW,respectively (Table 2). Caeine, the major alkaloidof tea (39), complexes with polyphenols in tea,mainly theaavins and this complex modies posi-tively the taste characteristics both caeine andtheaavins making the tea taste brisker (40). Caf-feine contents from this study were in accordancewith the previous studies (18, 41). However, 12.32-19.60 mg/g tea leaf (42) and 14.25-16.95 mg/g drymatter (25) of caeine contents, lower than ourresults, have been reported. Variation in caeine

content of teas is attributed to dierences in pluck-ing season of tea, processing method and varietyand structure of leaf (18, 41, 43, 44). Additionally,

caeine content of tea can vary widely dependingon the extraction conditions (3, 45). is studyshowed that tea samples contained much lowertheobromine than caeine. eobromine levelswere also lower than those reported by Khanchi etal. (42) and Sharma et al. (3). While signicant dif-ference was detected in caeine contents of teas,but not in theobromine contents. In general, 1st,2nd, 3rd and 7th grade teas contained signicantlyhigher content of caeine than 4th, 5th and 6th ones,which can be because of the fact that there hasbeen more caeine in young tea leaves than in oldones (17, 43, 44).

Antioxidant activity of black teas

According to the results shown in Table 2, the scav-enging activity of black tea extracts on DPPH radi-cal ranged from 8.23 to 8.84 g ascorbic acid/100gtea. DPPH method has been widely used in anti-oxidant activity studies of plant extracts (46-48).e method is based on the reduction of alcoholicDPPH solutions at 517 nm in the presence of anhydrogen donating antioxidant (49) and polyphe-nols have been reported to be potent hydrogen do-nators to the DPPH radical (50, 51) because of theirideal structural chemistry (52).is study showedthat 1st, 2nd, 3rd and 7th grade teas had higher activi-ties compared to 4th, 5th and 6th ones. is can beattributed to higher concentration of avonol gly-cosides and TF present in these tea extracts due

Table 2. Individual and total TFs, alkaloids (mg/g dry weight) and antioxidant activity (g ascorbic acid/100g tea) of different

grades black tea

Tea

grade TF-f TF-3-G TF-3-G TF-3,3-DG Total TF Caffeine TheobromineA.ox.

activity

1 3.870.24bc 5.490.10d 3.380.10de 5.840.01b 18.580.30c 25.970.53c 0.200.02a 8.840.05c

2 3.890.31bc 5.270.10cd 3.090.12cd 5.790.03b 18.040.49c 24.140.41ab 0.190.01a 8.560.03bc

3 3.680.29abc 5.100.15c 2.900.12bc 5.760.11b 17.430.46c 24.650.33b 0.190.01a 8.400.17ab

4 3.280.23ab 4.720.05b 2.560.09ab 5.120.13a 15.680.32b 24.080.17ab 0.180.01a 8.310.10ab

5 2.980.17a 4.230.09a 2.310.05a 4.740.16a 14.270.09a 23.160.33a 0.180.01a 8.230.08a

6 2.970.21a 4.190.09a 2.330.06a 4.690.22a 14.180.12a 23.030.41a 0.180.01a 8.300.05ab

7 4.340.25c 6.100.21e 3.640.24e 5.870.20b 19.950.85d 26.260.06c 0.200.01a 8.550.08bc

Means sharing different letter (a-e) in the same column are significantly different (P

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to the fact that there is a high correlation betweenantioxidant activity of plant extracts and polyphe-nols (53-57).

Conclusions

In seven grades Turkish black tea, two alkaloids (caf-feine and theobromine), two avan-3-ols (EGCGand ECG), three avonol glycosides (Q3RG, Q3Gand K3RG) and four individual TF (TF-f, TF-3-G,TF-3-G and TF-3,3-DG) were identied andquantied. Signicant dierences were detected inbiochemicals content and antioxidant activity be-tween dierent grades black teas. In general, the

contents of alkaloids, Q3RG, Q3G and TF in 1st

,2nd, 3rd and 7th grade teas and the contents of avan-3-ols in 4th, 5th and 6th grade teas were found to behigher. However, there was no signicant dier-ence in K3RG content of the teas. 1 st, 2nd, 3rd and7th grade teas showed also higher antioxidant activ-ity determined by DPPH radical assay. erefore,these results showed that 1st, 2nd, 3rd and 7th gradeteas had better quality. As explained in materialsand methods section, 1st, 2nd, 3rd and a part of 7th

gradeteas were not passed through crusher werealways valuable than others because of containingmore buds, so more active compounds.

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