The status of micronutrients (Cu, Fe, Mn, Zn) in tea and tea infusions in selected samples imported to the Czech Republic

Abstract

A total of 30 tea samples of different origins, thirteen green tea samples, thirteen black tea samples, two semi-fermented tea samples and one white tea, imported to the Czech Republic, were collected and analysed for the total content of copper, iron, manganese, and zinc in tea leaves and tea infusions. The total contents of metals in tea leaves differ according to the type of tea (green or black) and are probably influenced by many other factors, e.g. soil properties. The total contents of Mn were much higher compared to the total contents of Cu, Fe, and Zn, and varied between 511–2220 mg/kg. To compare easily hot water soluble concentrations of Cu, Fe, Mn and Zn, 5 min, 60 min, and 24 h infusions were prepared. The extractability of the elements was in the order Cu > Zn > Mn > Fe. The proportions of the element contents in the infusion related to the respective total contents in leaves were 30 ± 16% Cu, 26 ± 10% Zn, 18 ± 10% Mn, and 1.5 ± 0.8% Fe, respectively. The results confirmed that tea infusion can be an important dietary source of Mn.    

Comparison and Validation of Different Alternative Sample Preparation Procedures of Tea Infusions Prior to Their Multi-Element Analysis by FAAS and ICP OES

“…The use of other procedures, particularly the direct analysis of infusions with their no previous treatment, was found useless. Surprisingly, there are many contributions in the literature, in which the direct analysis of infusions of BTs and GTs was used (Altintig et al 2014;Dambiec et al 2013;Derun 2014;Diniz et al 2015;Froes et al 2014;Jeszka-Skowron et al 2015;Malik et al 2008;Mehra and Baker 2007;Memic et al 2014;Ozcan et al 2008;Ozdemir et al 2014;Street et al 2006). Unfortunately, in the overwhelming majority of cited papers (with exception for Diniz et al 2015;Froes et al 2014), no validation of sample preparation procedures used and results achieved was undertaken.…”

“…Such routine analyses can answer the question about the health risk of tea beverages (Jeszka-Skowron et al 2015;Ozdemir et al 2014). In addition, they can evaluate differences among black and green teas in reference to their nutritional value and the content of essential and other metals along with their contribution to recommended dietary intakes (RDIs) (Dash et al 2008;Derun 2014;Jeszka-Skowron et al 2015;Malik et al 2008;Mehra and Baker 2007;Memic et al 2014;PazRodriguez et al 2015;Ozdemir et al 2014;Street et al 2006;Schwalfenberg et al 2013;Tahir Soomro et al 2008).…”

“…The most popular and extensively used in the analysis of tea infusions are spectrochemical methods, including flame atomic absorption spectrometry (FAAS) (Dambiec et al 2013;Gallaher et al 2006;Malik et al 2008;Memic et al 2014;Paz-Rodriguez et al 2015;Polechonska et al 2015;Tahir Soomro et al 2008) and inductively coupled plasma optical emission spectrometry (ICP OES) (Altintig et al 2014;Dash et al 2008;Diniz et al 2015;Derun 2014;Fernandez et al 2002;Froes et al 2014;Malik et al 2008;Mehra and Baker 2007;Ozcan et al 2008;Ozdemir et al 2014;Salahinejad and Aflaki 2010;Street et al 2006). In case of FAAS, it is particularly convenient in reference to selected metals that are highly abounded in tea infusions, i.e., Ca, Fe, K, Mg, Mn, and Na (Szymczycha-Madeja et al 2012).…”

“…In addition, graphite furnace atomic absorption spectrometry (GFAAS) (JeszkaSkowron et al 2015;Wrobel et al 2000) and inductively coupled plasma mass spectrometry (ICP MS) (Milani et al 2015;Schwalfenberg et al 2013;Shen and Chen 2008;Sofuoglu and Kavcar 2008) were used. Among different sample preparation procedures reported so far for infusions of black (BTs) and green (GTs) teas before their spectrochemical analysis, it appears that no treatment and direct measurements of metals in them was preferred in case of FAAS (Dambiec et al 2013;Malik et al 2008;Memic et al 2014;Polechonska et al 2015), ICP OES (Altintig et al 2014;Derun 2014;Diniz et al 2015;Froes et al 2014;Malik et al 2008;Mehra and Baker 2007;Ozcan et al 2008;Ozdemir et al 2014;Street et al 2006, andGFAAS (Jeszka-Skowron et al 2015). In addition, infusions of teas were acidified with HNO 3 to a concentration of 0.28 mol L −1 (Salahinejad and Aflaki 2010) or 1.4 mol L −1 (Schwalfenberg et al 2013) or HCl to a concentration of 0.12 mol L −1 (Paz-Rodriguez et al 2015).…”

“…The UV photolysis-assisted digestion in H 2 O 2 , aimed at destructing the organic matrix of infusions of tea, was also carried out (Dash et al 2008). Unfortunately, reported methods of the direct analysis of infusions of BTs and GTs (Altintig et al 2014;Dambiec et al 2013;Derun 2014;Jeszka-Skowron et al 2015;Malik et al 2008;Mehra and Baker 2007;Memic et al 2014;Ozcan et al 2008;Ozdemir et al 2014;Street et al 2006), or their acidification (Salahinejad and Aflaki 2010;Schwalfenberg et al 2013) were not validated nor verified, therefore, the quality of the data achieved in above-cited works could be questioned. Although spike-and-recovery experiments were made in case of few direct analyses of infusions and quantitative recoveries were obtained, i.e., 91.9-113 % for infusions of GTs (Froes et al 2014) and 85.2-113 % for infusions of BTs and GTs (Diniz et al 2015), it should be noted that the recovery study is selectively used and does not have a high priority when another analytical method is available for comparison purposes.…”