Migration of Components from Cork Stoppers to Food: Challenges in Determining Inorganic Elements in Food Simulants T. Corona, M. Iglesias, and E. Anticó * Department of Chemistry, University of Girona, 17071 Girona, Spain * S Supporting Information ABSTRACT: The inorganic elements potentially migrating from cork to a food simulant [a hydroalcoholic solution containing 12 and 20% (v/v) ethanol] have been determined by means of inductively coupled plasma (ICP) with atomic emission and mass spectrometric detection. The experimental instrumental conditions were evaluated in depth, taking into account spectroscopic and nonspectroscopic interference caused by the presence of ethanol and other components in the sample. We report concentrations ranging from 4 μg kg −1 for Cd to 28000 μg kg −1 for Al in the food simulant (concentrations given in kilograms of cork). The values found for Ba, Mn, Fe, Cu, and Zn have been compared with the guideline values stated in EU Regulation 10/ 2011. In all cases, cork met the general safety criteria applicable to food contact material. Finally, we have proposed water as an alternative to the hydroalcoholic solution to simplify quantification of the tested elements using ICP techniques. KEYWORDS: elemental composition, cork, food simulant, migration, matrix interferences, spectroscopic interferences ■ INTRODUCTION Cork is a natural product obtained from the bark of Quercus suber, a common species in the Mediterranean region. Because of its unique physical properties, such as elasticity and low permeability, cork has long been used in the production of cork stoppers, frequently used in the wine industry to seal wine bottles. 1 The cork stopper fabrication process involves various steps: the stripping of the cork plank from the tree stem, a first rest or maturation in the field or factory, followed by boiling and resting in open air, a further boiling step and resting in the store room with a high relative humidity, and finally elimination of the outer corkback and the cork material cut and shaped according to use (stoppers for still wine and disks for sparkling wine). Surface modification is also performed using paraffins and other additives. 2 The chemical characterization of cork has been investigated mainly with respect to organic compounds. 3,4 However, little attention has been paid to determining its elemental composition. The sources of the inorganic elements present in cork bark and cork stoppers may differ. On the one hand, plants and trees can accumulate trace elements, especially heavy metals, and act as passive receptors; the uptake of nutrients and trace elements through the roots has been extensively studied. 5 On the other hand, contamination from atmospheric particles, pesticides, and the cork stopper fabrication process itself may also contribute to the distribution of metals in cork material. Some studies have addressed the mineral composition of cork material and its relationship with mineral nutrition, the climate, or tree characteristics. 6 In these cases, it is mainly nutrients that are analyzed. In addition, some authors have used tree barks as bioindicators of heavy metal pollution in the atmosphere because of their ability to accumulate metals. The role of bark as a cation exchanger has been highlighted. 7 Another very important issue to consider is the interaction of cork with wine when cork stoppers are used to seal wine bottles. European Regulation No. 1935/2004 (repealing Directives 80/590/EEC and 89/109/EEC) requires that food contact materials are safe and do not transfer their components into food in quantities that could endanger human health, change food composition in an unacceptable way, or deteriorate the taste and odor of the food. 8 Annex I of the regulation mentioned above lists the groups of materials that may be covered by speci fic measures, including cork. Speci fic regulations for cork are listed in Resolution ResAP(2004)2, adopted by the Committee of Ministers, in its composition restricted to Representatives of the States members of the Partial Agreement in the Social and Public Health Field. 9 Among other recommendations, the document states that Directives 82/711/EEC, 85/572/EEC, 93/8/EEC, 97/48/ EEC, and 2002/72/EEC and their future amendments should be applied, and that there should be verification of compliance with the quantitative restriction according to the conditions laid out in “Technical document No.2-test conditions and methods of analysis for cork stoppers and other cork materials and articles intended to come in contact with foodstuffs”. In this respect, a migration test should be performed under conditions simulating long-term storage (10 days at 40 °C) using a food simulant consisting of a 12% ethanol solution. The potential migrants from agglomerated cork stoppers associated with synthetic products (additives, surface treatments, and lubri- cants) have been previously studied in line with this approach. 10 In general, elemental concentration in food simulant solutions obtained from corks is expected to be very low, and for this reason, extremely sensitive analytical techniques are needed. A common technique for determining elements in aqueous matrices is by means of inductively coupled plasma Received: January 15, 2014 Revised: May 22, 2014 Accepted: May 26, 2014 Published: May 26, 2014 Article pubs.acs.org/JAFC © 2014 American Chemical Society 5690 dx.doi.org/10.1021/jf500170w | J. Agric. Food Chem. 2014, 62, 5690−5698