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Essential Element Contents of Turkish Black Tea
ESSENTIAL ELEMENT CONTENTS OF TURKISH BLACK TEA
2
Ayse Dilek Atasoy⁎, Mehmet Irfan Yesilnacar⁎, Ahmet Ferit Atasoy† *
Department of Environmental Engineering, Harran University, Sanliurfa, Turkey †Department of Food Engineering, Harran University, Sanliurfa, Turkey
2.1 Introduction Tea has gained the world’s taste in the past 2000 years as one of the most popular nonalcoholic beverages, next to water. The economic and social interest of tea is easily understood from the fact that about 18–20 billion cups of tea are consumed daily in the world (Mandiwana et al., 2011). Tea is grown in an area of 762,008 ha in Turkey. The annual tea production in Turkey and world was 212,400 and 5,345,523 tones, respectively. Black tea is generally processed by a fermentation method that allows for the effective action of polyphenol oxidase enzymes and this process causes the leaves to blacken. Drying is applied to stop the oxidation process, thereby resulting in a long-lasting, stable tea product (Robertson, 1992). The consumption of tea is regarded as an important source of several essential and nonessential elements, including major dietary elements (Ca, K, and Mg), minor and trace minerals (Cu, Fe, Mn, Na, Sr, and Zn), and heavy metals (Al, Cd, Cr, Ni, and Pb) (Szymczycha-Madeja et al., 2015). Tea drinking has both positive and negative impacts on human health (Dambiec et al., 2013). The health benefits of tea have been well documented. The beverage of tea may be an important source of essential major or mineral dietary inorganic elements (BrzezichaCirocka et al., 2016). Although tea is considered a healthy beverage, we should keep in mind its potentially toxic effects, which have been neglected in the past (Polechonska et al., 2015). C. sinensis (tea tree) was reported as an aluminum-accumulating plant in previous research works (Mossion et al., 2008). It also tolerates and accumulates elevated quantities of F and Pb (Szymczycha-Madeja et al., 2015). Atasoy et al. (2016) studied the fluoride content of Turkish and Ceylon teas and the Non-alcoholic Beverages. https://doi.org/10.1016/B978-0-12-815270-6.00002-5 © 2019 Elsevier Inc. All rights reserved.
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average daily fluoride intake of the human body. They determined the fluoride content of Turkish and Ceylon black and green tea infusions (2 g/100 mL) using an ion selective electrode. They identified dental fluorosis in school-age children because of the excessive intake of fluoride with black tea and the high-fluorine drinking water. Industrial wastes, agricultural applications, mining activities, and emissions are the main pollution sources of metals in the environment. Traces of undesirable and toxic metals from these sources can easily contaminate tea plants. Tea is known as a healthful beverage with bioactive molecules and high antioxidant activity (Mejia et al., 2009). Antioxidant activity is defined “as an limitation of the oxidation of proteins, lipids, DNA or other molecules that occurs by blocking the propagation stage in oxidative chain reactions” and primary antioxidants directly scavenge free radicals, while secondary antioxidants indirectly prevent the formation of free radicals through Fenton’s reaction (Huang et al., 2005). Black tea leaves and infusions include flavonoids such as oligomeric theaflavins and thearubigins formed in the oxidation process. 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. They exhibit antioxidant, antiinflammatory, antiallergic, and antimicrobial properties (Pękal et al., 2013). For the production of green tea, freshly gathered leaves are rapidly fried to inactivate the enzyme polyphenol oxidase, as a result of preventing fermentation and producing a dry, constant product. The fresh leaves are allowed to wither to produce black tea, until their moisture grade is lowered to <55% of the original leaf weight, which results in the concentration of polyphenols (PPs) in the leaves. The withered leaves are then rolled and crushed, initiating fermentation of the PPs. During these processes, the catechins (a group of natural PPs in green tea, accounting for its characteristic color and flavor) are converted to polymeric compounds, theaflavins (TFs) and thearubigins, consequently decreasing the catechin content (Khizar et al., 2015). The principal differences between green and black tea processing are presented in Fig. 2.1 (Cabrera et al., 2006). White tea is produced from unopened buds (categorized as silver needle) or from buds and immature leaves. All types of tea infusions also contain glycosides of flavonols, that is, quercetin, such as rutin and other quercetin derivatives, phenolic acids, and organic acids (Lin et al., 2008). Jeszka-Skowron et al. (2015) tested several tea samples such as white, green, black, and lemon-flavored ones. They measured antioxidant activity and observed a strong correlation between obtained results. Packed lemon tea infusions showed increased levels of rutin, quercetin, and phenolic acids. Nevertheless, the beneficial effect of the high level of dissociated phenolic compounds is also related
Chapter 2 Essentıal Element Contents of Turkish Black Tea 65
Tea leaves (Camellis sinensis) Polyphenols (catechins, principally)
Partial withering
Indoor withering
Steaming
Rolling
Rolling and drying
Total fermentation
Final firing
Final firing
Green tea
Black tea
Nonoxidised phenolic compounds/catechins (ECGC, EGC, ECG, EC)
Oxidised phenolic compounds/theaflavins thearubigins
Polyphenoloxidase action
Fig. 2.1 Principal differences between green and black tea processing and its influence on the final polyphenols content. From Cabrera, C., Artacho, R., Giménez, R., 2006. Beneficial effects of green tea—a review. J. Am. Coll. Nutr. 25 (2), 79–99.
with higher level of extracted toxic elements. Pękal et al. (2013) determined the mineral and flavonoid contents of commercially available different types of teas (premium black, flavored black, green, and fruit tea). They found that the flavonoids were predominantly present as glycosides. Rutin was determined 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. Tea infusion is prepared by pouring boiling hot water over cured leaves of the tea plant (Kottiappan et al., 2013). During tea brewing, both essential and trace elements are extracted into the beverage. It has a cooling, slightly bitter astringent flavor, which many people enjoy (Mandiwana et al., 2011). The significance of tea may be understood better if the chemical forms of elements are identified.
66 Chapter 2 Essentıal Element Contents of Turkish Black Tea
The essential element contents and metal concentrations were determined in Turkish black tea infusions and the compositions of Turkish and other teas are compared in this chapter.
2.2 Materials and Methods Ten Turkish black tea samples were provided from markets in Sanliurfa in 2016. All these samples were selected from the most commonly consumed brands in Turkey. Tea infusions were prepared by boiling 100 mL of deionized water and pouring the boiling water over 2.0 g of tea samples into a standardized Erlenmeyer flask. The tea infusion was stirred and covered with watch glasses. After 10 min, the extraction (tea infusion) was filtered through a filter paper (Whatman 42, 125 mm) into test tubes to eliminate any turbidity or suspended substance and after cooling to room temperature, the infusions were analyzed immediately. Tea infusion for each samples was repeated two times on different days. The analysis results are the average of 10 tea samples. Tea samples were analyzed for Al, Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, Pb, and Zn content in an inductively coupled plasma (ICP) mass spectrometer (PerkinElmer Optima 5300 DV model). Fluoride ions were analyzed using a Hach-Lange HQ40d Fluoride Meter (product code: 2589 99) using the TISAB (total-ionic strength adjustment buffer) method (Liu et al., 2010; APHA, 1998). All analyses were performed in duplicate.
2.3 Results and Discussion 2.3.1 Fluoride Content of Tea The fluoride content of tea infusion is listed in Table 2.1 by Atasoy et al., 2016. Fluoride concentrations ranged from 1.01 to 2.89 mg/L. The highest fluoride level was obtained for organic Turkish black tea while Ceylon green tea had the minimum F content. Turkish black and green tea infusions had higher fluoride concentration than Ceylon black and green tea. It was signified that black tea samples originally produced in Turkey had higher fluoride content than produced in Sri Lanka, India, and Kenya. Without considering tea origin and type, the fluoride level of organic tea infusions was higher than that of nonorganic ones. The fluoride concentrations of organic Turkish black and green tea infusion were 2.890 and 2.347 mg/L, respectively. The amount of transferred fluorine from the root through the tea leaves was related to the soil composition and the local environmental conditions.
Chapter 2 Essentıal Element Contents of Turkish Black Tea 67
Table 2.1 Fluoride Contents of Teas Tea Varieties
Fluoride Content (mg/L)
Turkish black tea Organic Turkish black tea Ceylon black tea Turkish green tea Organic Turkish green tea
1.69 2.89 1.14 1.47 2.35
From Atasoy, A.D., Yesilnacar, M.I., Atasoy, A.F., 2016. Evaluation of fluoride concentration and daily intake by human from tea infusions. Harran Tarım ve Gıda Bilimleri Dergisi 20(1), 1–6.
The fluoride intake of the human body is in the range of 30.2%– 50.0% and 48.3%–80.0% for adults and children, respectively. People are often exposed to various sources of fluoride by feeding, drinking, or breathing. The controlled consumption of tea, which is the most popular beverage in Turkey, is important to prevent the high uptake of fluoride. Excess traditional tea drinking with the consumption of high-fluoride drinking water increases the dental fluorosis risk in children. Fluorine in the body accumulates in bones and teeth in the form of hydroxyfluoroapatite. Fluorine is built into both dentine and enamel in teeth. The foods and/or beverages, the age, gender, and some other factors affect fluorine amount in the body. The fluorine concentration in the bones of young (20–30 years old) and old (70–80 years old) people are 200–800 and 1000–2500 mg/kg, respectively. Fluorine is present predominately in its inorganic form in the blood and its average concentration ranges from 10 to 200 μg/L (Sucman and Bednar, 2012; Atasoy et al., 2016).
2.3.2 Essential and Nonessential Element Contents of Tea The essential and nonessential element concentrations of tea infusions are listed in Table 2. The most abundant elements in infusions were K, Mg, Al, Ca, Mn, Na, Zn, Fe, Ni, and Cu. Potassium was found as the highest concentration in tea infusions while Cu was the lowest one. Cd, Cr, Hg, and Pb were not detected. K and Mn contents of Turkish black tea were found to be 286.68 and 6.85 mg/L, respectively. In the study by Dambiec et al. (2013), K was the most abundant element in all the tea samples tested. The average level of this metal was 17,600 mg/kg. They found the average
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Table 2 Element Concentrations in Turkish Black Tea Infusion Elements
Concentration (mg/L) (Average of 10 Turkish Black Tea Infusions)
Al Ca Cd Cr Cu Fe Hg K Mg Mn Na Ni Pb Zn
11.60 9.73 Not detected Not detected 0.08 0.16 Not detected 286.68 12.86 6.85 6.54 0.10 Not detected 0.24
total K content leached from tea to the infusion to be 60% and they classified this metal as highly extractable (>55%). They determined the lowest K content in tea from Argentina and Vietnam and the highest in tea from Central India. Kumar et al. (2005) and Soomro et al. (2008) also reported high K concentration in Indian and Chinese teas, respectively. Kumar et al. (2005) suggest that it may be specifically incorporated within a binding ligand in the tea leaves. Mahani and Maragheh (2011) observed that about 90% of the Na and K elements were extracted to tea infusions. They found a considerable amount of Mn in tea leaves. Despite the extraction efficiency of 50%, tea is a rich source of manganese. Average Cu and Zn concentrations in Turkish black tea infusions were determined to be 0.08 and 0.24 mg/L, respectively. Jin et al. (2008) claimed that people who consume large amounts of tea (e.g., 10 g of tea leaves per day) may not necessarily be at any risk as the daily intake of Cu from such tea drinking is less than 0.4 mg. This is true because the recommended daily consumption of Cu for adults as issued by the US Air Force is 1.5–3.0 mg (US AF, 1990). Welna et al. (2012) reported that when total concentrations of elements in tea infusions are measured and considered, it appears that the intake of 1 L of tea per day may contribute 2.0%–6.4% of
Chapter 2 Essentıal Element Contents of Turkish Black Tea 69
Cu, 89.5%–290% of Mn, and 1.3%–2.1% of Zn to the respective RDAs (Recommended Dietary Allowance) of these elements. Average Al and Fe contents of Turkish black tea infusions were found to be 11.6 and 0.16 mg/L, respectively. Polechonska et al. (2015) analyzed black teas in Poland for Zn, Mn, Cd, Pb, Ni, Co, Cr, Al, and Fe concentrations both in dry material and their infusions. Generally, the most abundant trace metals in both types of tea were Al and Mn. They found a wide variation in percentage transfer of elements from the dry tea materials to the infusions. Fe was insoluble and only a small portion of this metal content was determined in the infusion. With respect to the acceptable daily intake of metals, they found the infusions of teas analyzed to be safe for human consumption. Numerous studies have demonstrated the presence of Al in tea due to the acidic soils where tea plants are grown (Karak and Bhagat, 2010) as well as through tea processing. Some studies have revealed the high capacity of the tea plant to accumulate aluminum (Al), a neurotoxic element; therefore, it is necessary to control the intake of food with high amounts of this metal. One study reported that black tea contains approximately sixfold more Al than green tea, and the extraction of Al in black teas was higher than in the green teas. Aluminum is the most specific inorganic element in tea plants and tea leaves contain relatively higher Al than other plants (Shu et al., 2003). The variations in Al content may be due to different soil conditions, different harvesting periods, and the influence of the water quality (Khizar et al., 2015). Most of the elements in cured tea leaves, especially metals ions, are complexed by flavonols, catechols, tannins, and PPs. The content of tannins is negatively correlated with concentrations of Al, Cr, Cu, Fe, and Mn in tea infusions due to the binding of these metals and the formation of their insoluble complexes. Among different elements, Al seems to be the most strongly associated with polyphenolic compounds in the tea matrix. The chelating activity of PPs and caffeine toward Cu, Fe, and Zn is also high but lower than that established for Al. The lowest degree of the complexation by PPs can be observed for Mn (Welna et al., 2012). Barone et al. (2016) investigated the trace elements (Hg, Cd, Pb, Cu, Zn, Ni, Fe, Cr, and Se) in green and black tea marketed in Italy. They found Fe to be the most abundant element followed by Zn, Cu, Se, Ni, and Cr, whereas Pb was the predominant among the analyzed nonessential elements followed by Hg and Cd. Mg and Ca contents of Turkish black tea were found to be 12.86 and 9.73 mg/L, respectively. It appears that Mg is also quite easily extracted as a component of chlorophyll. Another alkaline earth element, that is, Ca is strongly trapped inside plant cells and for that reason extraction efficiencies for these elements are relatively lower. Differences in extraction efficiencies for transition metals, for example, Cu, Fe, Mn, Ni,
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and Zn, are difficult to explain, but they probably reflect the ionic and covalent characteristics of these elements (Matsuura et al., 2001). Na is one of the major constituents in black teas. In the present research, the average Na content was 6.54 mg/L. Soomro et al. (2008) and Yemane et al. (2008) noted higher Na contents in tea from China and Ethiopia (880 and 964 mg/kg, respectively). The percentage transfer of the total Na content to the infusion was lower than 65%, reported by Soomro et al. (2008). Szymczycha-Madeja et al. (2012) also classified Na as highly extractable (>55%). Both essential mineral elements and toxic metals are extracted into tea infusion. Studies showed that heavy metal contents of tea infusions were generally lower than those in tea leaves. Some trace elements are essential for the normal functioning of the human organism and several have health-promoting properties. The main sources of trace metals in plants are their growth media, nutrients, soil, and agrochemical inputs, including pesticides and fertilizers (Dambiec et al., 2013). The regular consumption of tea contributes to the daily dietary requirements of several essential elements. The highest metal content was affirmed in black tea while the lower metal content was in green tea and herbal tea (Mandiwana et al., 2011). Despite the high toxic element levels in some of tea leaf samples, trace element concentrations in infusions were measured to be at safe levels (Milani et al., 2016).
2.4 Conclusions Tea is a source of a large variety of essential and nonessential elements including major dietary metals (Ca, K, and Mg), minor and trace minerals (Cu, Fe, Mn, Na, Sr, and Zn), and heavy metals (Al, Cd, Cr, Ni, and Pb). It is considered a healthy beverage with bioactive molecules and high antioxidant activity. Generally, K was found as the most abundant macroelement in Turkish black tea followed by Mg, Al, Ca, Mn, and Na whereas Al was prominent among the trace metals tested, followed by Mn, Zn, Fe, Ni, and Cu. On the other hand, Cd, Cr, Hg, and Pb were not detected. While the tea plant has a strong potential to uptake and accumulate several elements from the soil, tea infusion may serve as a dietary source of different micronutrients for humans. However, different opinions also prevail about the safety of tea drinking by taking into consideration such nonessential or trace element accumulation in the human body. Tea is an Al-accumulating plant. It also tolerates and accumulates elevated quantities of F and Pb. For example, excessive intake of fluoride with black tea increased dental fluorosis cases in children. Thus, more focus should be placed on monitoring heavy metal contents in tea infusion and studying their health risk to tea consumers. The quality of tea plants and infusions should be determined to avoid overconsumption and their toxicities
Chapter 2 Essentıal Element Contents of Turkish Black Tea 71
in long-term use. Trace element contents of tea plants, their toxic effects, and intake by humans must be known. The origin of the tea as well as the water sources must also be regarded.
References APHA, 1998. Standard Methods for the Examination of Water and Wastewater, twentieth ed. American Public Health Association, Washington. Atasoy, A.D., Yesilnacar, M.I., Atasoy, A.F., 2016. Evaluation of fluoride concentration and daily intake by human from tea infusions. Harran Tarım ve Gıda Bilimleri Dergisi 20 (1), 1–6. Barone, G., Giacominelli-Stuffler, R., Storelli, M.M., 2016. Evaluation of trace metal and polychlorinated biphenyl levels in tea brands of different origin commercialized in Italy. Food Chem. Toxicol. 87, 113–119. Brzezicha-Cirocka, J., Grembecka, M., Szefer, P., 2016. Monitoring of essential and heavy metals in green tea from different geographical origins. Environ. Monit. Assess. 188, 183. Cabrera, C., Artacho, R., Giménez, R., 2006. Beneficial effects of green tea—a review. J. Am. Coll. Nutr. 25 (2), 79–99. Dambiec, M., Polechonska, L., Klink, A., 2013. Levels of essential and non-essential elements in black teas commercialized in Poland and their transfer to tea infusion. J. Food Compos. Anal. 31, 62–66. Huang, D., Ou, B., Prior, R.L., 2005. The chemistry behind antioxidant capacity assays. J. Agric. Food Chem. 53, 1841–1856. Jeszka-Skowron, M., Krawczyk, M., Zgola-Grzeskowiak, A., 2015. Determination of antioxidant activity, rutin, quercetin, phenolic acids and trace elements in tea infusions: influence of citric acid addition on extraction of metals. J. Food Compos. Anal. 40, 70–77. Jin, C.W., Du, S.T., Zhang, K., Lin, X.Y., 2008. Factors determining copper concentration in tea leaves produced at Yuyao County, China. Food Chem. Toxicol. 46 (6), 2054–2061. Karak, T., Bhagat, R.M., 2010. Trace elements in tea leaves, made tea and tea infusion: a review. Food Res. Int. 43 (9), 2234–2252. Khizar, H., Hira, I., Uzma, M., Uzma, B., Sobia, M., 2015. Tea and its consumption: benefits and risks. Crit. Rev. Food Sci. Nutr. 55 (7), 939–954. Kottiappan, M., Dhanakodi, K., Annamalai, S., Anandhan, S.V., 2013. Monitoring of pesticide residues in South Indian tea. Environ. Monit. Assess. 185, 6413–6417. Kumar, A., Nair, A.G.C., Reddy, A.V.R., Garg, A.N., 2005. Availability of essential elements in Indian and US tea brands. Food Chem. 89 (3), 441–448. Lin, L.-Z., Chen, P., Harnly, J.M., 2008. New phenolic components and chromatographic profiles of green and fermented teas. J. Agric. Food Chem. 56, 8130–8140. Liu, H., Deng, S., Li, Z., Yu, G., Huang, J., 2010. Preparation of Al–Ce hybrid adsorbent and its application for defluoridation of drinking water. J. Hazard. Mater. 179, 424–430. Mahani, M.K., Maragheh, M.G., 2011. Simultaneous determination of sodium, potassium, manganese and bromine in tea by standard addition neutron activation analysis. Food Anal. Methods 4, 73–76. Mandiwana, K.L., Panichev, N., Panicheva, S., 2011. Determination of chromium(VI) in black, green and herbal teas. Food Chem. 129, 1839–1843. Matsuura, H., Hokura, A., Katsuki, F., Itoh, A., Haraguchi, H., 2001. Multielement determination and speciation of major-to-trace elements in black tea leaves by ICPAES and ICP-MS with the aid of size exclusion chromatography. Anal. Sci. 2001 (17), 391–398.
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Mejia, E.G., Ramirez-Mares, M.V., Puangpraphant, S., 2009. Bioactive components of tea: cancer, inflammation and behavior. Brain Behav. Immun. 23, 721–731. Milani, R.F., Morgano, M.A., Cadore, S., 2016. Trace elements in Camellia sinensis marketed in southeastern Brazil: extraction from tea leaves to beverages and dietary exposure. LWT Food Sci. Technol. 68, 491–498. Mossion, A., Potin-Gautier, M., Delerue, S., Le Hecho, I., Behra, P., 2008. Effect of water composition on aluminium, calcium and organic carbon extraction in tea infusions. Food Chem. 106, 1467–1475. Pękal, A., Biesaga, M., Pyrzynska, K., 2013. Trace metals and flavonoids in different types of tea. Food Sci. Biotechnol. 22 (4), 925–930. Polechonska, L., Dambiec, M., Klink, A., Rudecki, A., 2015. Concentrations and solubility of selected trace metals in leaf and bagged black teas commercialized in Poland. J. Food Drug Anal. 23, 486–492. Robertson, A., 1992. In: Wilson, K.C., Clifford, M.N. (Eds.), The Chemistry and Biochemistry of Black Tea Production-the Non-Volatiles, Tea Cultivation to Consumption. Chapman and Hall, Springer, Netherlands, pp. 555–601. Shu, W.S., Zhang, Z.Q., Lan, C.Y., Wong, M.H., 2003. Fluoride and aluminium concentrations of tea plants and tea products from Sichuan Province, PR China. Chemosphere 52 (9), 1475–1482. Soomro, M.T., Zahir, E., Mohiuddin, S., Khan, A.N., Naqvi, I.I., 2008. Quantitative assessment of metals in local brands of tea in Pakistan. Pak. J. Biol. Sci. 11 (2), 285–289. Sucman, E., Bednar, J., 2012. Determination of fluoride in plant material using microwave induceed oxygen combustion. Czech J. Food Sci. 30 (5), 438–441. Szymczycha-Madeja, A., Welna, M., Pohl, P., 2012. Elemental analysis of teas and their infusions by spectrometric methods. Trends Anal. Chem. 35, 165–181. Szymczycha-Madeja, A., Welna, M., Pohl, P., 2015. Determination of essential and non-essential elements in green and black teas by FAAS and ICP OES simplified— multivariate classification of different tea products. Microchem. J. 121, 122–129. US AF (US Air Force), 1990. Copper. In: The Installation Program Toxicology Guide. vol. 5. Wright-Patterson Air Force Base, Ohio, pp. 1–43. Welna, M., Szymczycha-Madeja, A., Stelmach, E., Pohl, P., 2012. Speciation and fractionation of elements in tea infusions. Crit. Rev. Anal. Chem. 42 (4), 349–365. Yemane, M., Chandravanshi, B.S., Wondimu, T., 2008. Levels of essential and nonessential metals in leaves of the tea plant (Camellia sinensis L.) and soil of Wushwush farms, Ethiopia. Food Chem. 107 (3), 1236–1243.
2
Ayse Dilek Atasoy⁎, Mehmet Irfan Yesilnacar⁎, Ahmet Ferit Atasoy† *
Department of Environmental Engineering, Harran University, Sanliurfa, Turkey †Department of Food Engineering, Harran University, Sanliurfa, Turkey
2.1 Introduction Tea has gained the world’s taste in the past 2000 years as one of the most popular nonalcoholic beverages, next to water. The economic and social interest of tea is easily understood from the fact that about 18–20 billion cups of tea are consumed daily in the world (Mandiwana et al., 2011). Tea is grown in an area of 762,008 ha in Turkey. The annual tea production in Turkey and world was 212,400 and 5,345,523 tones, respectively. Black tea is generally processed by a fermentation method that allows for the effective action of polyphenol oxidase enzymes and this process causes the leaves to blacken. Drying is applied to stop the oxidation process, thereby resulting in a long-lasting, stable tea product (Robertson, 1992). The consumption of tea is regarded as an important source of several essential and nonessential elements, including major dietary elements (Ca, K, and Mg), minor and trace minerals (Cu, Fe, Mn, Na, Sr, and Zn), and heavy metals (Al, Cd, Cr, Ni, and Pb) (Szymczycha-Madeja et al., 2015). Tea drinking has both positive and negative impacts on human health (Dambiec et al., 2013). The health benefits of tea have been well documented. The beverage of tea may be an important source of essential major or mineral dietary inorganic elements (BrzezichaCirocka et al., 2016). Although tea is considered a healthy beverage, we should keep in mind its potentially toxic effects, which have been neglected in the past (Polechonska et al., 2015). C. sinensis (tea tree) was reported as an aluminum-accumulating plant in previous research works (Mossion et al., 2008). It also tolerates and accumulates elevated quantities of F and Pb (Szymczycha-Madeja et al., 2015). Atasoy et al. (2016) studied the fluoride content of Turkish and Ceylon teas and the Non-alcoholic Beverages. https://doi.org/10.1016/B978-0-12-815270-6.00002-5 © 2019 Elsevier Inc. All rights reserved.
63
64 Chapter 2 Essentıal Element Contents of Turkish Black Tea
average daily fluoride intake of the human body. They determined the fluoride content of Turkish and Ceylon black and green tea infusions (2 g/100 mL) using an ion selective electrode. They identified dental fluorosis in school-age children because of the excessive intake of fluoride with black tea and the high-fluorine drinking water. Industrial wastes, agricultural applications, mining activities, and emissions are the main pollution sources of metals in the environment. Traces of undesirable and toxic metals from these sources can easily contaminate tea plants. Tea is known as a healthful beverage with bioactive molecules and high antioxidant activity (Mejia et al., 2009). Antioxidant activity is defined “as an limitation of the oxidation of proteins, lipids, DNA or other molecules that occurs by blocking the propagation stage in oxidative chain reactions” and primary antioxidants directly scavenge free radicals, while secondary antioxidants indirectly prevent the formation of free radicals through Fenton’s reaction (Huang et al., 2005). Black tea leaves and infusions include flavonoids such as oligomeric theaflavins and thearubigins formed in the oxidation process. 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. They exhibit antioxidant, antiinflammatory, antiallergic, and antimicrobial properties (Pękal et al., 2013). For the production of green tea, freshly gathered leaves are rapidly fried to inactivate the enzyme polyphenol oxidase, as a result of preventing fermentation and producing a dry, constant product. The fresh leaves are allowed to wither to produce black tea, until their moisture grade is lowered to <55% of the original leaf weight, which results in the concentration of polyphenols (PPs) in the leaves. The withered leaves are then rolled and crushed, initiating fermentation of the PPs. During these processes, the catechins (a group of natural PPs in green tea, accounting for its characteristic color and flavor) are converted to polymeric compounds, theaflavins (TFs) and thearubigins, consequently decreasing the catechin content (Khizar et al., 2015). The principal differences between green and black tea processing are presented in Fig. 2.1 (Cabrera et al., 2006). White tea is produced from unopened buds (categorized as silver needle) or from buds and immature leaves. All types of tea infusions also contain glycosides of flavonols, that is, quercetin, such as rutin and other quercetin derivatives, phenolic acids, and organic acids (Lin et al., 2008). Jeszka-Skowron et al. (2015) tested several tea samples such as white, green, black, and lemon-flavored ones. They measured antioxidant activity and observed a strong correlation between obtained results. Packed lemon tea infusions showed increased levels of rutin, quercetin, and phenolic acids. Nevertheless, the beneficial effect of the high level of dissociated phenolic compounds is also related
Chapter 2 Essentıal Element Contents of Turkish Black Tea 65
Tea leaves (Camellis sinensis) Polyphenols (catechins, principally)
Partial withering
Indoor withering
Steaming
Rolling
Rolling and drying
Total fermentation
Final firing
Final firing
Green tea
Black tea
Nonoxidised phenolic compounds/catechins (ECGC, EGC, ECG, EC)
Oxidised phenolic compounds/theaflavins thearubigins
Polyphenoloxidase action
Fig. 2.1 Principal differences between green and black tea processing and its influence on the final polyphenols content. From Cabrera, C., Artacho, R., Giménez, R., 2006. Beneficial effects of green tea—a review. J. Am. Coll. Nutr. 25 (2), 79–99.
with higher level of extracted toxic elements. Pękal et al. (2013) determined the mineral and flavonoid contents of commercially available different types of teas (premium black, flavored black, green, and fruit tea). They found that the flavonoids were predominantly present as glycosides. Rutin was determined 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. Tea infusion is prepared by pouring boiling hot water over cured leaves of the tea plant (Kottiappan et al., 2013). During tea brewing, both essential and trace elements are extracted into the beverage. It has a cooling, slightly bitter astringent flavor, which many people enjoy (Mandiwana et al., 2011). The significance of tea may be understood better if the chemical forms of elements are identified.
66 Chapter 2 Essentıal Element Contents of Turkish Black Tea
The essential element contents and metal concentrations were determined in Turkish black tea infusions and the compositions of Turkish and other teas are compared in this chapter.
2.2 Materials and Methods Ten Turkish black tea samples were provided from markets in Sanliurfa in 2016. All these samples were selected from the most commonly consumed brands in Turkey. Tea infusions were prepared by boiling 100 mL of deionized water and pouring the boiling water over 2.0 g of tea samples into a standardized Erlenmeyer flask. The tea infusion was stirred and covered with watch glasses. After 10 min, the extraction (tea infusion) was filtered through a filter paper (Whatman 42, 125 mm) into test tubes to eliminate any turbidity or suspended substance and after cooling to room temperature, the infusions were analyzed immediately. Tea infusion for each samples was repeated two times on different days. The analysis results are the average of 10 tea samples. Tea samples were analyzed for Al, Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, Pb, and Zn content in an inductively coupled plasma (ICP) mass spectrometer (PerkinElmer Optima 5300 DV model). Fluoride ions were analyzed using a Hach-Lange HQ40d Fluoride Meter (product code: 2589 99) using the TISAB (total-ionic strength adjustment buffer) method (Liu et al., 2010; APHA, 1998). All analyses were performed in duplicate.
2.3 Results and Discussion 2.3.1 Fluoride Content of Tea The fluoride content of tea infusion is listed in Table 2.1 by Atasoy et al., 2016. Fluoride concentrations ranged from 1.01 to 2.89 mg/L. The highest fluoride level was obtained for organic Turkish black tea while Ceylon green tea had the minimum F content. Turkish black and green tea infusions had higher fluoride concentration than Ceylon black and green tea. It was signified that black tea samples originally produced in Turkey had higher fluoride content than produced in Sri Lanka, India, and Kenya. Without considering tea origin and type, the fluoride level of organic tea infusions was higher than that of nonorganic ones. The fluoride concentrations of organic Turkish black and green tea infusion were 2.890 and 2.347 mg/L, respectively. The amount of transferred fluorine from the root through the tea leaves was related to the soil composition and the local environmental conditions.
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Table 2.1 Fluoride Contents of Teas Tea Varieties
Fluoride Content (mg/L)
Turkish black tea Organic Turkish black tea Ceylon black tea Turkish green tea Organic Turkish green tea
1.69 2.89 1.14 1.47 2.35
From Atasoy, A.D., Yesilnacar, M.I., Atasoy, A.F., 2016. Evaluation of fluoride concentration and daily intake by human from tea infusions. Harran Tarım ve Gıda Bilimleri Dergisi 20(1), 1–6.
The fluoride intake of the human body is in the range of 30.2%– 50.0% and 48.3%–80.0% for adults and children, respectively. People are often exposed to various sources of fluoride by feeding, drinking, or breathing. The controlled consumption of tea, which is the most popular beverage in Turkey, is important to prevent the high uptake of fluoride. Excess traditional tea drinking with the consumption of high-fluoride drinking water increases the dental fluorosis risk in children. Fluorine in the body accumulates in bones and teeth in the form of hydroxyfluoroapatite. Fluorine is built into both dentine and enamel in teeth. The foods and/or beverages, the age, gender, and some other factors affect fluorine amount in the body. The fluorine concentration in the bones of young (20–30 years old) and old (70–80 years old) people are 200–800 and 1000–2500 mg/kg, respectively. Fluorine is present predominately in its inorganic form in the blood and its average concentration ranges from 10 to 200 μg/L (Sucman and Bednar, 2012; Atasoy et al., 2016).
2.3.2 Essential and Nonessential Element Contents of Tea The essential and nonessential element concentrations of tea infusions are listed in Table 2. The most abundant elements in infusions were K, Mg, Al, Ca, Mn, Na, Zn, Fe, Ni, and Cu. Potassium was found as the highest concentration in tea infusions while Cu was the lowest one. Cd, Cr, Hg, and Pb were not detected. K and Mn contents of Turkish black tea were found to be 286.68 and 6.85 mg/L, respectively. In the study by Dambiec et al. (2013), K was the most abundant element in all the tea samples tested. The average level of this metal was 17,600 mg/kg. They found the average
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Table 2 Element Concentrations in Turkish Black Tea Infusion Elements
Concentration (mg/L) (Average of 10 Turkish Black Tea Infusions)
Al Ca Cd Cr Cu Fe Hg K Mg Mn Na Ni Pb Zn
11.60 9.73 Not detected Not detected 0.08 0.16 Not detected 286.68 12.86 6.85 6.54 0.10 Not detected 0.24
total K content leached from tea to the infusion to be 60% and they classified this metal as highly extractable (>55%). They determined the lowest K content in tea from Argentina and Vietnam and the highest in tea from Central India. Kumar et al. (2005) and Soomro et al. (2008) also reported high K concentration in Indian and Chinese teas, respectively. Kumar et al. (2005) suggest that it may be specifically incorporated within a binding ligand in the tea leaves. Mahani and Maragheh (2011) observed that about 90% of the Na and K elements were extracted to tea infusions. They found a considerable amount of Mn in tea leaves. Despite the extraction efficiency of 50%, tea is a rich source of manganese. Average Cu and Zn concentrations in Turkish black tea infusions were determined to be 0.08 and 0.24 mg/L, respectively. Jin et al. (2008) claimed that people who consume large amounts of tea (e.g., 10 g of tea leaves per day) may not necessarily be at any risk as the daily intake of Cu from such tea drinking is less than 0.4 mg. This is true because the recommended daily consumption of Cu for adults as issued by the US Air Force is 1.5–3.0 mg (US AF, 1990). Welna et al. (2012) reported that when total concentrations of elements in tea infusions are measured and considered, it appears that the intake of 1 L of tea per day may contribute 2.0%–6.4% of
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Cu, 89.5%–290% of Mn, and 1.3%–2.1% of Zn to the respective RDAs (Recommended Dietary Allowance) of these elements. Average Al and Fe contents of Turkish black tea infusions were found to be 11.6 and 0.16 mg/L, respectively. Polechonska et al. (2015) analyzed black teas in Poland for Zn, Mn, Cd, Pb, Ni, Co, Cr, Al, and Fe concentrations both in dry material and their infusions. Generally, the most abundant trace metals in both types of tea were Al and Mn. They found a wide variation in percentage transfer of elements from the dry tea materials to the infusions. Fe was insoluble and only a small portion of this metal content was determined in the infusion. With respect to the acceptable daily intake of metals, they found the infusions of teas analyzed to be safe for human consumption. Numerous studies have demonstrated the presence of Al in tea due to the acidic soils where tea plants are grown (Karak and Bhagat, 2010) as well as through tea processing. Some studies have revealed the high capacity of the tea plant to accumulate aluminum (Al), a neurotoxic element; therefore, it is necessary to control the intake of food with high amounts of this metal. One study reported that black tea contains approximately sixfold more Al than green tea, and the extraction of Al in black teas was higher than in the green teas. Aluminum is the most specific inorganic element in tea plants and tea leaves contain relatively higher Al than other plants (Shu et al., 2003). The variations in Al content may be due to different soil conditions, different harvesting periods, and the influence of the water quality (Khizar et al., 2015). Most of the elements in cured tea leaves, especially metals ions, are complexed by flavonols, catechols, tannins, and PPs. The content of tannins is negatively correlated with concentrations of Al, Cr, Cu, Fe, and Mn in tea infusions due to the binding of these metals and the formation of their insoluble complexes. Among different elements, Al seems to be the most strongly associated with polyphenolic compounds in the tea matrix. The chelating activity of PPs and caffeine toward Cu, Fe, and Zn is also high but lower than that established for Al. The lowest degree of the complexation by PPs can be observed for Mn (Welna et al., 2012). Barone et al. (2016) investigated the trace elements (Hg, Cd, Pb, Cu, Zn, Ni, Fe, Cr, and Se) in green and black tea marketed in Italy. They found Fe to be the most abundant element followed by Zn, Cu, Se, Ni, and Cr, whereas Pb was the predominant among the analyzed nonessential elements followed by Hg and Cd. Mg and Ca contents of Turkish black tea were found to be 12.86 and 9.73 mg/L, respectively. It appears that Mg is also quite easily extracted as a component of chlorophyll. Another alkaline earth element, that is, Ca is strongly trapped inside plant cells and for that reason extraction efficiencies for these elements are relatively lower. Differences in extraction efficiencies for transition metals, for example, Cu, Fe, Mn, Ni,
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and Zn, are difficult to explain, but they probably reflect the ionic and covalent characteristics of these elements (Matsuura et al., 2001). Na is one of the major constituents in black teas. In the present research, the average Na content was 6.54 mg/L. Soomro et al. (2008) and Yemane et al. (2008) noted higher Na contents in tea from China and Ethiopia (880 and 964 mg/kg, respectively). The percentage transfer of the total Na content to the infusion was lower than 65%, reported by Soomro et al. (2008). Szymczycha-Madeja et al. (2012) also classified Na as highly extractable (>55%). Both essential mineral elements and toxic metals are extracted into tea infusion. Studies showed that heavy metal contents of tea infusions were generally lower than those in tea leaves. Some trace elements are essential for the normal functioning of the human organism and several have health-promoting properties. The main sources of trace metals in plants are their growth media, nutrients, soil, and agrochemical inputs, including pesticides and fertilizers (Dambiec et al., 2013). The regular consumption of tea contributes to the daily dietary requirements of several essential elements. The highest metal content was affirmed in black tea while the lower metal content was in green tea and herbal tea (Mandiwana et al., 2011). Despite the high toxic element levels in some of tea leaf samples, trace element concentrations in infusions were measured to be at safe levels (Milani et al., 2016).
2.4 Conclusions Tea is a source of a large variety of essential and nonessential elements including major dietary metals (Ca, K, and Mg), minor and trace minerals (Cu, Fe, Mn, Na, Sr, and Zn), and heavy metals (Al, Cd, Cr, Ni, and Pb). It is considered a healthy beverage with bioactive molecules and high antioxidant activity. Generally, K was found as the most abundant macroelement in Turkish black tea followed by Mg, Al, Ca, Mn, and Na whereas Al was prominent among the trace metals tested, followed by Mn, Zn, Fe, Ni, and Cu. On the other hand, Cd, Cr, Hg, and Pb were not detected. While the tea plant has a strong potential to uptake and accumulate several elements from the soil, tea infusion may serve as a dietary source of different micronutrients for humans. However, different opinions also prevail about the safety of tea drinking by taking into consideration such nonessential or trace element accumulation in the human body. Tea is an Al-accumulating plant. It also tolerates and accumulates elevated quantities of F and Pb. For example, excessive intake of fluoride with black tea increased dental fluorosis cases in children. Thus, more focus should be placed on monitoring heavy metal contents in tea infusion and studying their health risk to tea consumers. The quality of tea plants and infusions should be determined to avoid overconsumption and their toxicities
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in long-term use. Trace element contents of tea plants, their toxic effects, and intake by humans must be known. The origin of the tea as well as the water sources must also be regarded.
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