Contribution of tea (Camellia sinensis L.) to recommended daily intake of Mg, Mn, and Fe: An in vitro bioaccessibility assessment

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Highlights

  • Leachabilites and bioaccessibilities of Mg, Mn, and Fe from teas were studied.

  • Effect of infusion time on extractability and availability were determined.

  • Contributions of lemon juice, sugar, calcium, tannic acid, or milk were assessed.

  • Percent leachability of Mg with time was larger than those of Mn and Fe.

  • Mn was the most bioaccessible element in black, earl grey, and green teas.

Abstract

This study outlines the determination of total elemental contents, time-dependent extractabilities, and bioaccessibilities of Mg, Mn, and Fe from nine tea samples, including black, earl grey, and green teas, using inductively coupled plasma mass spectrometry. Leachabilities and bioaccessibilities were evaluated using samples infused for 2, 5, and 10 min, and bioaccessible levels were determined after in vitro enzymatic digestion. Lemon juice, sugar, milk, calcium, and tannic acid were studied as additives, and found to increase or decrease the bioaccessibilities from black tea infusions. Drinking one cup of tea provided 0.16%, 0.01%, and 0.10% of the recommended dietary allowance of Mg for black, earl grey, and green teas infused for 2 min, respectively. The equivalent levels were 11%, 6%, and 7% for Mn, and 0.05%, 0.02%, and 0.02% for Fe in the same samples, respectively. Therefore, Mn was found to be the most bioaccessible element resulting from tea consumption, reaching 17%–24% of the recommended daily allowance in the 10-min infusion. Moreover, lemon juice was found to increase the bioaccessibility of Mn by up to 3.4-fold, even in tea samples infused for 2 min.

Introduction

Tea (Camellia sinensis L.) is one of the oldest and most popular non-alcoholic beverages consumed globally after water (Szymczycha-Madeja et al., 2012; Yemane et al., 2008), with black tea leaves comprising approximately 78% of global annual production (Pinto, 2013). Three types of tea, namely, black, oolong, and green, are the most frequently consumed teas in Western countries, China and Taiwan, and Asian and north African countries, respectively (Liebman and Murphy, 2007; Welna et al., 2013).

In addition to an inherently complex matrix (Kumar et al., 2005; Szymczycha-Madeja et al., 2012; Yemane et al., 2008), tea leaves are rich in several elements present at mg g−1, μg g−1, or ng g−1 levels (Kumar et al., 2005). The distinctive elemental content of any tea is mostly attributed to the manufacturing processes and various local environmental conditions from plant growth to end product (Seenivasan et al., 2008; Soylak et al., 2007; Welna et al., 2013). Inductively coupled plasma mass spectrometry (ICP-MS) has emerged as the most powerful technique for quantifying elements in tea leaves and infusions because of its high sensitivity and selectivity, low detection limits, multielement determination capability, wide dynamic linear ranges, and ability to measure isotope ratios in tea leaves and infusions compared with other monoelemental or multielemental analytical techniques (Nardi et al., 2009; Szymczycha-Madeja et al., 2012; Vrcek and Vrcek, 2012; Welna et al., 2013).

The elemental content of teas can have both beneficial and toxic effects on human health through regular consumption (Karak and Bhagat, 2010; Szymczycha-Madeja et al., 2012) and has, therefore, received much research interest (Soylak et al., 2007). However, total element concentrations might not reflect the true availability, with bioaccessible levels (i.e., elemental levels readily absorbed into the gastrointestinal tract) considered more important for risk assessment studies (Erdemir and Gucer, 2014, Erdemir and Gucer, 2015; Intawongse and Dean, 2006; Lei et al., 2013).

In recent years, tea components have been widely reported, with the potential health effects of different tea types and many of their constituents having been extensively studied (Dufresne and Farnworth, 2001; Jain et al., 2013; Pinto, 2013). As habitual tea consumption can significantly contribute to the daily intake of several elements (Pekal et al., 2013; Welna et al., 2013), dietary exposure from tea infusions (Brzezicha-Cirocka et al., 2016a; Karak and Bhagat, 2010; Kumar et al., 2005; Milani et al., 2016; Street et al., 2006; Szymczycha-Madeja et al., 2012; Yemane et al., 2008), time-dependent extractabilities, and additive contributions have been reported. For example, Street et al. (2006) studied the hot water solubilities of Cu, Fe, Mn, and Zn with different infusion times. The influence of lemon juice as an additive to black and earl grey tea infusions decreased Mn concentrations and increased Fe concentrations, while in green teas the opposite was observed, with increased Mn concentrations (Derun, 2014). Furthermore, milk and lemon have also been shown to affect aluminum bioavailability (Street et al., 2007). Nevertheless, bioavailability or bioaccessibility have not been widely discussed, with few elements studied in this context (Ganji and Kies, 1994; Mehra and Baker, 2007; Mehra et al., 2013; Szymczycha-Madeja et al., 2013; Yokel and Florence, 2008).

This study aimed to evaluate the bioaccessibilities of Mg, Mn, and Fe as representative essential and/or macro-elements from three commonly consumed tea types (black, green, and earl grey tea) and assess their potential health risks using enzymatic in vitro methods after ICP-MS analysis. The time-dependent extractability and availability were also studied. Further experiments were conducted on tea infusions with added lemon juice, table sugar, or milk, representing widespread and traditional consumption habits, and their effects on element bioaccessibilities were evaluated. Moreover, any contribution of calcium from the diet or tannic acid, an inhibitor naturally found in tea leaves, were investigated by adding standard solutions of these substances to tea infusions before enzymatic digestion. Therefore, the leachability, in vitro bioaccessibility with time, and influence of consumption habits on bioaccessible levels were assessed as an extension of previous studies. Such an extensive bioaccessibility study has not previously been performed on tea samples.

Section snippets

Chemicals and reagents

A multielement standard solution containing Mg, Mn, and Fe (each 100 μg mL−1; instrument calibration standard 2) and a single-element standard solution of Ca (1000 μg mL−1) were purchased from Perkin Elmer (Lakewood, NJ, USA) and Inorganic Ventures (Lakewood, NJ, USA), respectively. “NCS ZC73014 tea leaves” certified reference material was obtained from the National Analysis Center for Iron and Steel (Beijing, China). Suprapur HNO3 (65%) and HCl (30%) were provided by local suppliers of Merck

Results and discussion

The total levels of Mg, Mn, and Fe calculated from the microwave-digested and 100-fold-diluted samples are shown in Table 1. From the total levels, magnesium was the most abundant element in the leaves. Furthermore, the total elemental levels of all the teas studied were considered to be significantly different (P < 0.05). This difference could be attributed to numerous environmental factors (Street et al., 2006). Measured isotopes, detection limits, and other validation parameters are shown in

Conclusions

Knowledge of the daily intake of Mg, Mn, and Fe resulting from the regular consumption of tea, obtained from in vitro studies, is important, despite these elements being considered essential. The teas studied were found to be good sources of Mg, Mn, and Fe, with high total contents of these elements in infusions. Despite these high levels, the bioaccessibilities of these elements are more important for assessing the risk factors of drinking tea. Among the elements, Mn showed a different

Conflict of interest

The author declares no conflicts of interest.

Acknowledgments

A part of this study was presented at the 7th Black Sea Basin Conference on Analytical Chemistry, 10–15 September 2015, in Varna, Bulgaria. The author is grateful to Professor Dr. Seref Gucer for invaluable discussions regarding the tea matrix. The Commission of Scientific Research Projects of Uludag University [to U. S. Erdemir, Project No. F-2008/25] is gratefully acknowledged for providing ICP-MS. I thank Simon Partridge, PhD, from Edanz Group (www.edanzediting.com/ac) for editing a draft of

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