Contents lists available at ScienceDirect Food and Chemical Toxicology journal homepage: www.elsevier.com/locate/foodchemtox Contrasting allocation of magnesium, calcium and manganese in leaves of tea (Camellia sinensis (L.) Kuntze) plants may explain their different extraction efficiency into tea Paula Pongrac a,∗ , Roser Tolrà b , Roghieh Hajiboland c , Katarina Vogel-Mikuš a,d , Mitja Kelemen a,e , Primož Vavpetič a , Primož Pelicon a , Juan Barceló b , Marjana Regvar d , Charlotte Poschenrieder b a Jožef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia b Laboratorio de Fisiología Vegetal, Facultad de Biociencias, Universidad Autónoma de Barcelona, 08193, Bellaterra, Spain c Department of Plant Science, University of Tabriz, 51666-16471, Tabriz, Iran d Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000, Ljubljana, Slovenia e Jožef Stefan International Postgraduate School, Jamova 39, 1000, Ljubljana, Slovenia ABSTRACT During tea preparation mineral elements are extracted from the dried leaves of tea (Camellia sinensis (L.) Kuntze) plants into the solution. Micro-particle induced X- ray emission was employed to investigate the spatial distribution of magnesium (Mg), calcium (Ca) and manganese (Mn) in the young and old leaves of tea plants grown in the absence and presence of aluminium (Al) in the substrate. Results revealed that in tea leaves the largest concentrations of Mg occurred in the epidermis, of Ca in oxalate crystals and of Mn in epidermis and oxalate crystals; there was a leaf-age effect on tissue-specific concentrations of Mg, Ca and Mn with all tissues of old leaves containing larger concentrations of Mg, Ca and Mn than young leaves; supplementation of substrate with Al reduced concentrations of Mg, Ca and Mn in the old leaves, and a link between the distribution of Mg, Ca and Mn in the tea leaves with the extraction efficiencies of these elements into the tea was possible. We conclude that old leaves of tea plants cultivated under conditions of low Al availability will have the largest concentrations of Mg, Ca and Mn and may represent most acceptable ingredient for the preparation of tea. 1. Introduction Beside coffee, tea is the most consumed hot beverage in the world. Taste and quality of tea and, in consequence, consumer acceptance, largely depend on the metabolic composition of the processed leaves of the tea plant (Camellia sinensis (L.) Kuntze), which are used to prepare this beverage (Gramza et al., 2005). Besides being a rich source of antioxidants, tea is considered to be a good provider of essential ele- ments, such as magnesium (Mg), phosphorus (P), sulphur (S), po- tassium (K), calcium (Ca), manganese (Mn), iron (Fe) and zinc (Zn) (Malik et al., 2008). To date, less is known about elemental composition than about metabolic composition of tea infusion. In the increasing need to ensure sufficient amounts of essential elements often lacking in our diets, which has negative effects on our health and productivity, this topic is gaining recognition (Bouis and Saltzman, 2017; White and Broadley, 2009). Simultaneously, food safety issues in relation to the intake of metal(loid)s, need to be addressed to ensure maximal allowed amounts in the diet(s) are not exceeded (Peng et al., 2018; Zhang et al., 2018). The elemental composition of the tea infusion depends on (i) the initial total element composition of tea leaves, (ii) the processing methodology of the tea leaves, (iii) the extraction conditions, and (iv) the extraction efficiency of the particular element (Karak and Bhagat, 2010). The initial total element concentrations in tea leaves depend on both environmental factors (particularly the soil characteristics) and plant factors (e.g. leaf age) (Carr et al., 2003; Fung et al., 2008; Peng et al., 2018). Their extraction, in turn, depends on the time allowed for the extraction process (Pohl and Prusisz, 2007), the temperature used for the extraction (Taşcioğlu and Kök, 1998), the solution(s) used (Mossion et al., 2008; Xu et al., 2017), and the chemical environment of the elements in the leaves (Özdemir and Güçer, 1998). While numerous studies report on the large differences among the commercially-sold teas in the total concentrations of elements and their leachability into the infusions (Malik et al., 2008; Street et al., 2006; Szymczycha- Madeja et al., 2012), the information on elemental composition the tea plant leaves remains scarce. The tea plant is an aluminium (Al) accumulator and tea leaves (Carr et al., 2003; Fung et al., 2008; Watanabe et al., 2007) as well as com- mercially-sold tea (Karak and Bhagat, 2010; Matsumoto et al., 1976; Ščančar et al., 2004; Szymczycha-Madeja et al., 2012) contain large https://doi.org/10.1016/j.fct.2019.110974 Received 20 September 2019; Received in revised form 11 November 2019; Accepted 13 November 2019 ∗ Corresponding author. E-mail address: paula.pongrac@ijs.si (P. Pongrac). Food and Chemical Toxicology xxx (xxxx) xxxx 0278-6915/ © 2019 Published by Elsevier Ltd. Please cite this article as: Paula Pongrac, et al., Food and Chemical Toxicology, https://doi.org/10.1016/j.fct.2019.110974