Trace Metals and Flavonoids in Different Types of Tea

Food Sci. Biotechnol. 22(4): 925-930 (2013) DOI 10.1007/s10068-013-0165-y RESEARCH ARTICLE Trace Metals and Flavonoids in Different Types of Tea Ann...
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Food Sci. Biotechnol. 22(4): 925-930 (2013) DOI 10.1007/s10068-013-0165-y

RESEARCH ARTICLE

Trace Metals and Flavonoids in Different Types of Tea Anna Pękal, Magdalena Biesaga, and Krystyna Pyrzynska

Received: 28 November 2012 / Revised: 23 January 2013 / Accepted: 14 February 2013 / Published Online: 31 August 2013 © KoSFoST and Springer 2013

Abstract The mineral and flavonoid contents of commercially available different types of teas (premium black, flavored black, green, and fruit tea) and the infusions produced from them were determined. Studied teas differed in the contents of elements between their raw materials and infusions. Iron and copper exhibited the lowest efficiency of extraction by hot water. For the most popular black tea brand (Lipton® Yellow label) the efficiency of metal extraction decreased in the order: Co>Mn>Ni>Zn>Cu>Fe. Flavored black Citrus tea infusion had the highest content of Co and Ni, while Yellow label and Green Indonesia are a good source of Fe, Mn, and Zn. Flavonoids were predominantly present as glycosides. Rutin was present at much higher levels in black and green teas. Significant amounts of naringin and hesperidin were determined in tea infusions with citrus aromas or fruits. Keywords: tea, trace metal, flavonoid, extraction efficiency

Introduction Tea infusion, a popular beverage consumed wordwide, is obtained from the leaves of one kind of a plant named Camellia sinensis. Tea leaves are primarily manufactured as green, black, or oolong, with black tea representing approximately 80% of tea products consumed. They differed in appearance, organoleptic taste, chemical content as well as flavor due to their respective fermentation process (1). In addition, various kinds of flavored or fruit teas became popular in many European countries due to their fragrance, therapeutic application, and lower content of caffeine, which could inhibit calcium absorption (2). These teas

contain natural aromas as well as dry fruits or herbs, which are added to tea leaves in the last stage of processing before packing. In recent years, tea has been extensively investigated mainly regarding its influence on human health. Regular intake of tea is associated with an improved antioxidant status in vivo that may contribute to lowering the risk of coronary heart disease, atherosclerosis, reduced mutagenicity, and inflammation (3,4). Flavonoids are the most abundant polyphenolic compounds in fresh tea leaves and extracts, and they are primarily responsible for the beneficial healthful properties of tea (5). They exhibit antioxidant, antiinflammatory, antiallergic, and antimicrobial properties. In addition to organic compounds, different minerals, and trace metals, which play a vital role in the metabolic processes, are present in tea leaves and their infusions (6,7). These elements are contained in enzymes and activate them, thereby in an essential way influencing biochemical processes in cells. The regular consumption of tea may contribute to the daily requirements of several elements. Generally, the metal content of the tea is influenced by the soil composition and local environmental factors. Various extraction conditions for preparation of tea infusion have been studied, such as brewing time, temperature, and addition of milk (8-10). The quality of a cup of tea remains dependent on the quality of tea leaf and kind of water used for brewing. The objective of this study was to determine the mineral content of commercially available different types of dry teas (premium black, flavored black, green, and fruit tea) as well as the concentration of metals and selected flavonoids in their infusions.

Materials and Methods Anna Pękal, Magdalena Biesaga, Krystyna Pyrzynska () Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland Tel: +4822-8220211; Fax: +4822-8223532 E-mail: [email protected]

Sample preparation All bagged teas Lipton® brand were purchased from a local market. This includes premium black tea Yellow label, Green Indonesia, flavored black tea

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Citrus, which contains except tea leaves also dry fruit and natural aroma of orange, lemon, grapefruit and limon, and fruit tea Delight citrus with the addition of rosehip, apple, lemon, and grapefruit peels. A bag of a given tea (1.8-2.0 g) was dipped into a 100 mL of freshly boiled distilled water to represent the typical quantity consumed by tea drinkers. After 10 min of brewing the samples were filtered through the Whatman filter paper (0858 grade). Dried sample of 0.250 g of each tea was mineralized in the presence of concentrated HNO3 (3 mL) and HF (0.2 mL) in the microwave oven. The power was gradually increased at 160 W for 3 min, at 350 W for 4 min, 750 W for 5 min, and finally 1,000 W for 6 min. After cooling the residue was transferred into a volumetric flask and made up to 25 mL with distilled water. For each kind of tea, digestion was made in triplicate. Digestion of a reagent blank was performed in parallel. Determination of metal ions A quadrupole spectrometer ICP-QMS (ELAN 6100 DRC; Perkin-Elmer Sciex, Boston, MA, USA) equipped with conventional Scott spray chamber and Meinhard nebulizer was used for the determination of metal ions. The working conditions of spectrometer were optimized daily in order to obtain the maximal sensitivity and stability. The operating conditions were as follows: plasma Ar gas flow rate 15 L/min, auxiliary Ar gas flow rate 1.2 L/min, nebulizer gas flow rate 0.74 L/min, solution uptake rate 1 mL/min, dwell time 100 min, and the number of replicates 6. The isotopes 63Cu, 57Fe, 61Ni, and 66Zn were used for quantification. 103Rh was used as internal standard. During measurements, care was taken to avoid memory effect and therefore wash-out time of 20 min was applied. All standard solutions used were prepared by appropriate dilution of 1 mg/mL single element standard solutions from Merck (Darmstadt, Germany). HPLC analysis Chromatographic analysis was performed with a Shimazu LC system consisted of binary pumps LC20-AD. Degasser DGU-20A5, column oven CTO-20AC, autosampler SIL-20AC, and 3200 QTRAP mass spectrometer (Applied Biosystem/MDS SCIEX, Framingham, MA, USA). A MS system equipped with electrospray ionization source (ESI) operated in negative ion mode and

a quadruple mass analyser in a scan mode from 50 to 1,500 m/z. ESI conditions were as follows: capillary temperature 450oC, curtain gas at 0.3 MPa, auxiliary gas at 0.3 MPa, and negative ionization mode source voltage 4.5 kV. Nitrogen was used as curtain and auxiliary gas. For each compound the optimum conditions of multiple reaction mode (MRM) were determined in the infusion mode (11). Flavonoids were separated on KinetexTM (Phenomenex, Torrance, CA, USA) C18 column (100×2.1, 2.6 µm) with precolumn at 30oC. Formic acid (2 mM, pH 2.8) as eluent A and acetonitrile as eluent B were used. The mobile phase was delivered at 0.2 mL/min in linear gradient mode: 0-5 min 20% B, 10-15 min 25% B, 20-25 min 30% B, 30-31 min 90% B, and 32 min 20% B. Compounds were identified by comparing retention time and m/z values, obtained by MS and MS/MS with the mass spectra from standards tested under the same conditions. Quantification of flavonoids was done from the calibration curves obtained in selected reaction monitoring (SRM) mode. Statistical analysis The tea dry samples and the infusions for the experiments were prepared separately from 3 bags of a given tea. All analyses were run in triplicate and mean values, together with standard deviations, are presented.

Results and Discussion Metal content in dry teas In the present work, 7 metals (Cu, Fe, Mn, Co, Pb, Ni, and Zn) in 4 commercially available teas and their infusions were determined. These teas represent different kinds as premium black, flavored black, green, and fruit teas. The results of the analysis of dry tea samples are presented in Table 1. All studied samples contained significant values of microelements but their contents presented a wide variability. The highest content was found for Mn, particularly for green tea (588.9 mg/kg) and black flavored teas (594.9 mg/ kg). Fruit tea contained the lowest content of Mn (114.9 mg/kg). The comparison performed by Kumar et al. (12) revealed that most of tea leaves from various countries have Mn content in the range of 300-900 mg/kg, except for those from Turkey and Japan (1,100-2,678 mg/kg). Studied black teas contained the highest level of Fe

Table 1. Contents of Cu, Fe, Mn, Co, Pb, Ni, and Zn in the studied teas Tea brand Yellow label Green Indonesia Citrus Delight citrus 1)

Mean±SD (n=3)

(mg/kg)

Cu

Fe

Mn

Co

Pb

Ni

Zn

025.3±1.31) 13.6±1.0 16.9±1.4 04.80±0.34

344±27.5 135±11.0 202±16.2 76.4±6.10.

251±20 589±47 595±42 115±81

0.18±0.02 0.27±0.02 0.57±0.05 0.21±0.02

0.80±0.06 fruit tea (Table 2). Gallaher et al. (15) determined much higher Zn concentrations in 9 herbal teas (16.5-108.5 mg/kg), while the range of 10.1-55.4 mg/kg was reported in tea (Camellia sinensis) plants by Nookabkaew et al. (16). Flavored black tea was rich in Co (0.56 mg/kg) and premium black tea in Pb (0.80 mg/kg). Plants can take up Pb from the soil and inevitably, a portion will be transported to the tea leaves. Older tea leaves tended to contain higher concentration of lead than younger leaves, and washing tea leaves with distilled water decreased average metal concentration up to 43% (17). The content of metals in black tea leaves was generally higher (except for Mn and Co) than in those of green tea (Table 1). In the production process, black tea leaves are air-dried before fermentation, while green tea leaves are steamed with water vapor, thus there is a possibility of some losses of the elements during this process. Metal content in tea infusions The level of metal concentration in the studied tea infusions may be affected by a number of parameters such as organic matrix of corresponding tea, original mineral content, kind of water used for brewing as well as extraction conditions (amount of material relative to water, infusion time, and temperature). The effectiveness of metal transfer from dry tea leaves to

infusion is shown in Fig. 1. The results are presented after subtraction of metal concentration in the water used as a blank. As can be seen, the percentage transfer of each metal varied widely for the different tea samples. Generally, Fe and Cu had the lowest percent release in all infusions. Although Lipton® Yellow label tea contained the largest amount of copper (25.3 mg/kg), the efficiency of extraction was lower than from Delight citrus tea, which contained the lowest content of this metal (4.8 mg/kg). Similar situation was observed for extraction of iron. The concentration of Fe in Citrus tea infusion was below the limit of detection (0.09 mg/L). The low extractability of Fe was also reported and dominating metal fraction in the infusions was the cationic form, which is considered as the most bioavailable (18). Its percentage contribution was determined to be 52 and 41%, respectively, for green and black tea. The extraction efficiency for Co, Ni, and Zn from tea leaves exceeded 40%, except for Co from Citrus tea. Although Citrus and Green tea were very rich in Mn (Table 1), the percent release of this metal was only in the range of 25-42%, in contrast to infusions prepared from Lipton® Yellow label and Delight citrus teas (Fig. 1). Interestingly, the toxic element Pb, was not leached from Yellow label and Green Indonesia (data not shown). However, it could be easily extracted from Delight citrus with the efficiency of 25-74%, the highest rate for spring water. Since different research reports employed different approaches to prepare tea infusions samples, direct comparison of the results is difficult. Taking into consideration the most popular black tea brand such as Lipton® Yellow label, the efficiency of metal extraction decreased in the order Mn>Co>Ni>Zn>Cu>Fe. The content of metals in tea infusions may be affected by different properties or structures of plants as well as level of polyphenolic compounds which could bind metals (19). The studied tea infusions, particularly Yellow label and Green Indonesia, could be a good source of Mn, which is in agreement with literature data (12,20). Manganese is an essential element and is bound to a number of essential

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Fig. 1. Efficiency of metal extraction from studied tea. ND, not detected

Fig. 2. Total ion chromatogram (TIC) in SRM mode of Delight citrus tea extract and extracted ion chromatogram of selected flavonoids.

enzymes; for example the activity of superoxide dismutase is suppressed by low Mn status. Copper is involved in energy production and it aids in the formation of red blood cells, bone, and hemoglobin. It is also essential to nerve health as it is needed to build and maintain myelin, the insulating sheath that surrounds nerve cells. Citrus tea infusion had relatively high contents of Cu, Co, and Ni.

However, the actual bioavailability and toxicity of trace elements to the human organisms depend not only on the total element amount of the metals but also on their existing physicochemical forms (21). Apparently, the trace and major metals can be present in the brews as simple ions but also as the complexes formed with the endogenous bioligands. Pohl and Prusisz (18) reported that Zn was

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present mainly in tea infusion in the cationic forms which account for 58-71 and 84-86%, respectively, in the black and the green teas. Manganese can be present in brews not only in the form of the predominant simple cations or other small cationic species (up to 80%) but also may be bound with the polyphenolic species or other macromolecular compounds (22). Total Al content of 10-19% in black tea infusion was present as cationic species, while about 2833% of as hydrolyzable polyphenolic compounds (23). Content of selected flavonoids The example of the chromatogram of Delight citrus tea infusion by LC/MS/MS is shown in Fig. 2 and the contents of some relevant flavonoids found in examined tea infusions are presented in Table 2. Flavonoids are predominantly present as glycosides rather than as aglycones. Luteolin was found at trace levels only in Yellow label and Citrus brand. The content of quercetin was higher in black tea (0.17 mg/L) than in other studied infusions. Rutin (quercetin-3rutinoside) was present at much higher level in black and green teas. Significant amounts of naringin (naringenin-7rutinoside) were determined in tea samples with citrus aromas or fruits such as Delight citrus and Citrus. Naringenin and hesperidin (hesperetin-7-rutinoside) were not found in premium black tea. It was found that supplementation with hesperidin and naringin significantly reduced blood glucose (24), while the bone and lipid benefits of hesperidin make it an attractive dietary agent for the management of the health of postmenopausal women (25). Thus, these flavored and fruit teas would support the human diet with a satisfactory source of naringenin and hesperidin. In relation to the presence of catechins (flavan-3-ols), their much higher contents in the analyzed infusions were found in Green Indonesia, followed by Citrus, Yellow label, and Delight citrus teas. The high antioxidant activity of these compounds has been widely described (5). The concentrations of epigallocatechin 3-gallate (EGCG), the major polyphenolic constituent of green tea, ranged from 0.024 to 128.1 mg/L. EGCG decreased in amount with increasing fermentation process from green to oolong and black tea as did total catechins (26). Acknowledgments The authors would like to thank the Structural Research Laboratory (SRL) at the Department of Chemistry of University of Warsaw (Warsaw, Poland) for making HPLC-MS measurements possible. SRL has been established with financial support from European Regional Development Found in the Sectorial Operational Programme ‘Improvement of the Competitiveness of Enterprises, Year 2004-2005’ project no: WPK_1/ 1.4.3./1/2004/72/72/165/ 2005/U.

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