Migration of Components from Cork Stoppers to Food: Challenges in

Article pubs.acs.org/JAFC

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

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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 © 2014 American Chemical Society

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 specific measures, including cork. Specific 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 lubricants) 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: Revised: Accepted: Published: 5690

January 15, 2014 May 22, 2014 May 26, 2014 May 26, 2014 dx.doi.org/10.1021/jf500170w | J. Agric. Food Chem. 2014, 62, 5690−5698

Journal of Agricultural and Food Chemistry

Article

Prior to analysis, a precise weight of cork soak was taken, and the desired amount of the internal standard (IS) solution was added. A small volume of HNO3 was also added to acidify the sample. To determine the total content of elements in cork samples, the following procedure was followed.16 Nine milliliters of concentrated HNO3 and 1 mL of hydrogen peroxide were added to a 0.5 g cork sample placed in a Teflon reactor. Once the vessel was sealed, it was placed in the microwave oven and the following program was run: 5 min to reach 180 °C, 10 min at 180 °C, and finally a cooling period. After cooling to ambient temperature, the reactor was opened, and the resultant solution was quantitatively transferred to a vial, where the total weight was carefully measured. To prepare the samples for analysis, the necessary amount of the IS solution was added to 5 g of the digested solution. The samples were measured using the prepared calibration set, as explained below. To avoid the presence of ethanol in the samples and standards, we tried other migration treatments. In particular, we evaluated the possibility of performing the migration tests by using water instead of a hydroalcoholic solution at different temperatures. Determination of Elements in the Food Simulant. For Minor and Trace Element Determination (Ba, Mn, and Al). Standard solutions were prepared in water or a hydroalcoholic solution. The calibration standards were prepared from individual standard solutions in 1% HNO3, containing Y (1 mg L−1) or Rh (3 mg L−1) as an internal standard, as indicated. IS correction was conducted by taking into account the intensity of the line for the measured element and for the internal standard. Additionally, because of the different behavior traditionally observed for ionic and atomic lines, each ionic line was corrected using an ionic line from the internal standard and each atomic line was corrected using an atomic line15 (see Table 1).

(ICP), which allows reliable results and high sample throughput. Depending on concentration level, different detection systems are available, such as ICP-AES (atomic emission spectroscopy) for elements present at concentrations higher than ∼0.1 mg L−1 and ICP-MS (inductively coupled plasma with mass spectrometry detection) for those present at lower concentrations. The latter technique shows good analytical performance but suffers from interferences of different types, such as matrix and spectroscopic interferences.11 In the particular case of a hydroalcoholic solution, the presence of a carbon source such as ethanol is of special concern. For example, some polyatomic interferences have been described for Cr (12C40Ar and 13C40Ar).12 Additionally, the determination of elements with low ionization potential such as Zn, Se, and As is also challenging because of the increase in their degree of ionization in the plasma when an additional carbon source is simultaneously present.13−15 To overcome these problems, several strategies were developed, including complex sample treatment procedures, the use of interference equations, collision cell devices, and highresolution instruments.15 In this study, we have assessed the elemental composition of a food simulant originating from cork soaks with two objectives: (1) providing a reliable method for their determination, avoiding, if possible, the use of ethanol in calibration standards, and (2) ascertaining whether cork may be considered a safe material for use as a stopper for bottled wine according to the aforementioned EU directive.

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Table 1. Selected Atomic and Ionic Lines for ICP-AES Measurements

MATERIALS AND METHODS

Reagents. The reagents used were analytical grade suprapur quality: nitric acid (Suprapur, Merck, Darmstadt, Germany) and hydrogen peroxide (Trace Select, Fluka, Gilligham, Dorset, U.K.). Water obtained from a Milli-Q purifier system (Millipore Corp., Bedford, MA) was used throughout the study. For matrix matching standards, ethanol absolute (UV-IR-HPLC) PAI was used, from Panreac. Monoelemental ICP standard solutions (1000 or 5000 mg L−1 for Ba) for each element studied were purchased from Pure Chemistry, ROMIL, UKAS calibration. Apparatus. An ETHOS PLUS Milestone microwave with an HPR1000/10S high-pressure rotor (Sorisole, Bergamo, Italy) was employed for acid digestion of samples. A sequential inductively coupled plasma atomic emission spectrometer (ICP-AES, Liberty RL, Varian) in radial configuration was used for major and minor element determination. For trace element determination, a quadrupole-based ICP-MS system (Agilent 7500c, Agilent Technologies, Tokyo, Japan) was used, equipped with an octapole collision reaction cell. Sample Collection. Samples consisting of cork granules (samples C1 and C2) and cork slabs (C3) were obtained from local producers in Girona, Spain. In all cases, the cork material was obtained from the cork residues discarded in the final stages of the production process, i.e., shaping of the cork slab to obtain the cork stoppers or cork disks. Theses residues are ground in the manufacturing to obtain cork granules intended to be used in the fabrication of different synthetic cork and other cork types (samples C1 and C2). In the case of cork sample 3, we obtained from the producer cork slices that were ground in our laboratory using a conventional grinder (Moulinette D56, Moulinex España, Barcelona, Spain). Sample Treatment. The migration tests were performed according to the European Directive using a hydroalcoholic (HA) solution [12% (v/v) ethanol] as a food simulant. Four grams of cork granules or previously ground cork slabs was immersed in 100 mL of a food simulant solution at 40 °C for a period of 10 days.10 The solid parts were then separated by filtering the sample through glass wool.

element

line type

wavelength (nm)

IS

line type

wavelength (nm)

Ba Zn Cu Fe Mn Al

II II I II II I

455.403 202.551 324.754 259.940 257.610 396.152

Y Y Rh Y Y Rh

II II I II II I

371.030 371.030 343.489 371.030 371.030 343.489

For Ultratrace Element Determination (Cr, Fe, Ni, Cu, Zn, Pb, Cd, As, and Se). From the commercial standard solutions, an intermediate solution in 1% (w/w) HNO3 containing the measured elements over the appropriate range of concentrations was prepared and used to obtain the calibration set, either in water or in a hydroalcoholic solution. The isotope 103Rh was used for internal standard correction after checking that it was not present in the samples at the concentration range studied (results from a semiquantitative analysis). The concentration of IS in the standard solutions prepared for calibration and in the samples was around 3.7 ng g−1. The experimental conditions for determining this set of elements were optimized taking into account different criteria: abundance of the selected isotope, correction of isobaric and polyatomic interferences under the vented or pressurized collision cell, type and flow rate of the gas used in the pressurized collision cell, correction of matrix interferences by the IS used, and finally the presence of other matrix interferences that cannot be corrected with the IS. Octopole and quadrupole potentials were varied according to cell conditions, being fixed at −12 and −11.1 V, respectively, when a pressurized cell was used and −6.4 and −4.5 V, respectively, under vented conditions. Some other parameters, such as ion lens settings, were adjusted daily to obtain the maximal sensitivity and precision. The oxide level (CeO+) and doubly charged ion level (Ce2+) were kept under 1 and 3%, respectively. 5691

dx.doi.org/10.1021/jf500170w | J. Agric. Food Chem. 2014, 62, 5690−5698


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Figure 1. Calibration curves for Al and Mn with and without IS. Statistical Analysis. The statistical package provided by Excel was used to perform analysis of variance to evaluate whether differences between treatments were significant (p < 0.05).

Table 2. Main Isotopes and Possible Interferences isotope

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56

Fe 57 Fe 60 Ni 62 Ni 63 Cu 65 Cu

RESULTS AND DISCUSSION Evaluation of Experimental Conditions for Determining Elements. The elements of interest were selected

111

Cd Pb 52 Cr 53 Cr 75 As 76 Se 78 Se 80 Se 64 Zn 66 Zn 68 Zn 208

interferences 40

Ar16O, 40Ca16O, 40Ar15N1H, 38Ar18O, 37Cl18O1H 40 16 1 Ar O H, 40Ca16O1H, 40Ar17O, 38Ar18O1H, 38Ar19F 44 Ca16O, 23Na37Cl, 43Ca16O1H 46 16 Ti O, 23Na39K, 46Ca16O 31 16 P O2, 40Ar23Na, 36Ar12C14N1H 49 16 Ti O, 32S16O21H, 40Ar25Mg, 40Ca16O1H, 36Ar14N21H, 32S33S, 32 16 17 S O O, 33S16O2, 12C16O37Cl, 12C18O35Cl, 31P16O18O − − 40 12 Ar C, 38Ar14N, 35Cl17O, 35Cl16O1H 40 13 Ar C, 37Cl16O 40 35 Ar Cl 40 36 Ar Ar 40 38 Ar Ar 40 40 Ar Ar 40 24 Ar Mg, 64Ni36Ar12C16O, 38Ar14N2 40 26 Ar Mg, 38Ar28Si, 38Ar14N2 40 14 Ar N2, 36Ar32S, 36Ar16O2, 38Ar14N16O

derived from the sample itself. In a previous work dealing with wine samples,17 we evaluated the influence of the presence of ethanol and demonstrated that use of an adequate IS allows the calibration set to be prepared in water instead of a HA solution. For this reason, we devoted much effort here to studying whether choosing an adequate IS makes it possible to appropriately correct the different types of interferences. The elements determined by ICP-AES will be discussed separately from those measured by ICP-MS in the following sections. Metals Determined by ICP-AES (Ba, Mn, and Al). Table 1 shows the selected atomic and ionic lines taken for measure-

Figure 2. Results obtained for Mn determination in a cork soak under different calibration conditions.

according to the results of preliminary semiquantitative studies conducted in our laboratory. To quantify these elements using ICP-AES and ICP-MS techniques, matrix interferences and spectral interferences are of great concern because of the presence of ethanol and other carbon sources in the matrix 5692



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standards in a hydroalcoholic solution with IS. The results obtained (Figure 2) demonstrate that the aqueous standards, even with IS, do not allow the correct determination of this element. On the other hand, when ethanol standards are used, the same result is obtained with and without IS, so the presence of ethanol is the main matrix effect in manganese determination. Metals Determined by ICP-MS (Cr, Fe, Ni, Cu, Zn, Pb, Cd, As, and Se). For those elements present at lower concentrations, ICP-MS was used. In this case, spectroscopic and nonspectroscopic interferences are of particular concern and different situations can be envisaged: (1) when matrix interference due to the presence of ethanol in the samples is corrected by use of the appropriate IS, (2) when polyatomic interferences exist that are corrected by the use of a pressurized cell and the conditions in the cell need to be optimized, and (3) elements with a high ionization potential that also need special instrumental conditions. We performed separate experiments depending on the characteristics of each element. Cadmium, Lead, Iron, Nickel, and Copper. For lead and cadmium, no important polyatomic interferences have been described. Therefore, the most abundant isotope was selected for their measurement. Calibration curves were measured in water and hydroalcoholic solutions both with IS, and results showed that the use of the internal standard allows appropriate correction for the presence of ethanol in the solution. In both cases, without using the pressurized collision cell, calibration could be performed with standards prepared in water. Additionally, the values obtained for Cd and Pb, measured in a sample obtained from soaked cork, showed no significant differences when both calibration sets were used and with IS

Table 3. Isotope and Cell Conditions Selected for ICP-MS Measurements isotope 111

Cd 208 Pb 56 Fe 60 Ni 63 Cu 53 Cr 66 Zn 75 As 78 Se

conditions vented cell vented cell He at 2 mL min−1 He at 2 mL min−1 He at 2 mL min−1 He at 2 mL min−1 He at 0.5 mL min−1 and H2 at 3 mL min−1 He at 0.5 mL min−1 and H2 at 3 mL min−1 He at 0.5 mL min−1 and H2 at 3 mL min−1

ment. The main problem associated with determining the elements is sample composition due to the presence of the alcohol, which may cause differences in nebulization efficiency and aerosol transport compared to those of water samples. Figure 1 shows calibration curves for Al and Mn (see Table S1 of the Supporting Information for calibration parameters). As we can see, the addition of Rh and Y as internal standards allows for an appropriate correction of matrix interference due to the presence of ethanol for Al. Similar results were obtained for Ba. For Mn, calibration curves are statistically different [p < 0.05 (see Table S2 of the Supporting Information)] for both matrices even in the presence of the internal standard, which means that matrix effects other than nebulization efficiency and transport contribute to the response at the selected wavelength. To verify this fact, a sample was measured in triplicate and the manganese concentration was determined using the calibration plots shown in Figure 1, i.e., aqueous standards, aqueous standards with IS, standards in a hydroalcoholic solution, and

Figure 3. Calibration curves for 56Fe under different conditions (pressurized cell with He at 2 mL min−1 and IS correction). 5693



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observed in all six cases (two isotopes for each element): the use of the pressurized cell with He at 2 mL min−1, as previously described,18 allows for a good correction of polyatomic interferences, while matrix interferences deriving from the presence of ethanol can be mostly overcome by employing IS correction. The most abundant isotope providing better sensitivity was then chosen (Table 3). In Figure 3 and Table S3 of the Supporting Information, the case of 56Fe is depicted by way of example. The experimental conditions were verified by analyzing the three metal cations in a cork soak (Figure 4). When the results obtained from calibration with water standards were compared with those obtained with the hydroalcoholic solution, no significant differences were obtained for Ni and Cu if the IS is used for quantification. For Fe, the matrix interferences are not adequately corrected, and it is therefore compulsory to perform calibration using hydroalcoholic solutions. It should be taken into account that the cork soak solution has a complicated composition, so other matrix effects, different from those related to ethanol content, may be present. Chromium. As explained in the Introduction, determination of chromium by means of ICP-MS is hampered by the presence of spectroscopic interferences due to the presence of carbon or chlorine in the sample matrix (see Table 2). Several strategies for overcoming these interferences have been proposed in the literature.12 When the instrumentation available was taken into account, the use of pressurized cell conditions with He was chosen as the best alternative. As preliminary work, different He flow rates in the collision reaction cell were tested to obtain a high signal background ratio (SBR). A rate of 2 mL min−1 was finally chosen as a compromise between a low level of interferences and sufficient analyte signal. Calibration curves, with standards in water or a hydroalcoholic solution, were obtained under different conditions (vented and pressurized cell conditions and with and without IS) for the most abundant chromium isotopes, 52Cr and 53Cr. Additionally, the effect of the presence of chloride was also evaluated, because Cl has been determined to be an abundant element in cork.19 The addition of helium in chromium determination decreases spectroscopic interferences, which can be observed in Figure 5. However, the presence of a fairly important spectroscopic interference is still observed when 52Cr is measured. In contrast, the use of He at a rate of 2 mL min−1 in the collision cell virtually eliminates the interference on 53Cr. The use of IS does not result in much difference in this case. Because chromium was present at a concentration level below the limit of detection in our particular samples, it could not be determined in the cork soak. Arsenic, Zinc, and Selenium. These elements are also difficult to determine by means of ICP-MS because of their high ionization potential, which produces a low degree of ionization in the plasma. Additionally, they also suffer from spectroscopic interferences (see Table 2). It is already known that some of these elements show an important increase in sensitivity in ICP-MS when a quite large amount of C is present in the plasma source.13 This effect has been explained as a charge transfer process from C ions to these elements and has been extensively studied for As and Se.20 Some studies also include other elements with high ionization potentials, like Zn.21 The presence of important polyatomic interferences in As, Se, and Zn measurements makes it necessary to use pressurized cell conditions. Some studies found in the literature conclude

Figure 4. Results obtained for determination of 56Fe, 60Ni, and 63Cu in a cork soak under different conditions.

correction. Some differences were encountered when the values obtained for calibration with ethanol were compared with the results obtained for calibration with ethanol and IS, probably due to matrix interferences other than ethanol. For Ni, Fe, and Cu, common polyatomic interferences are known (see Table 2). Calibration data were compared for the most abundant isotopes under different conditions (internal standard and vented or pressurized cell). Similar behavior is 5694



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Figure 5. Intensity for 52Cr and 53Cr under different conditions in the collision cell. IS is used in all cases.

recoveries are listed in Table 4. Recovery values were obtained by using calibration curves with hydroalcoholic standards, with and without the IS correction. If we compare the data in the table for those elements measured with ICP-AES, the need to use the internal standard becomes clear because recoveries in the range of 130−176% were obtained without IS. On the other hand, no statistical differences were obtained between the results for the other measured elements (recoveries obtained using calibration with IS compared with those without IS), except for As and Se. Taking into account the fact that the use of an IS is recommended in ICP-MS to account for variations in the plasma signal during one single run, we adopted this procedure to prepare the calibration set in the hydroalcoholic matrix. Migration Tests. To calculate the percentage of an element that has migrated to the simulant, we previously determined the total concentration of each element in the three different cork samples (C1−C3). To do this, we used microwave-assisted acid digestion, establishing the condition described in the experimental part. Table 5 shows the concentrations found. We have also included some values obtained from the literature in the table. As shown in the table, few data are available for microelements. The results reported from PIXE analyses obtained from the bulk layer of a cork stopper19 do not significantly differ from those obtained in our work in the case of Cu, while for Fe and Mn, PIXE concentrations are lower than ours. Additionally, when Pb is determined in a cork stopper used to seal a bottle of a French wine,22 a relatively high concentration at the end in contact with the wine was found, compared with the concentration at the center of the cork. In this context, it has to be considered that lead content in wines is regulated,23 and for that reason, its concentration in

that the use of H2 together with a small amount of He in the reaction cell (H2 at 3 mL min−1 and He at 0.5 mL min−1) gives good results for the determination of As and Se.15 We therefore decided to use these conditions in our measurements. In the case of Zn, we compared the results obtained using He at 2 mL min−1 (same conditions used for Cr, Ni, Fe, and Cu) and H2 at 3 mL min−1 and He at 0.5 mL min−1 (same conditions used for As and Se). Both gave similar results, so we decided to use the latter because of the greater sensitivity obtained in this case. Upon comparison of the calibration curves obtained with and without ethanol and using IS, the internal standard does not correct properly for any of these elements, as expected. As already mentioned, the signal enhancement produced, due probably to a higher degree of ionization in the plasma, which in turn is related to the presence of C atoms from the matrix, is observed only for elements with high ionization potentials; this is not the case with Rh (our IS). The use of ethanol matrix standards to obtain the calibration curves is therefore once again compulsory. When a cork soak was measured (see Figure 6) and the results were compared, we again observed a difference between calibration in an aqueous matrix and calibration in a hydroalcoholic solution, both with IS. When standards in water are used, the concentration of these three elements is overestimated. In Table 3, final collision cell conditions are summarized for the determination of arsenic, zinc, and selenium. Method Validation. Because of the lack of certified cork soaked material, we validated the final conditions by performing recovery experiments. Three cork soaks were obtained, one for each sample type (C1−C3), and element concentrations were measured. The desired amount of stock solution was then added and a new measurement performed. Spiked levels and 5695



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Table 4. Recovery Results (R) Obtained for Spiked Samples

Al Ba Mn Cr Fe Ni Cu Zn As Se Pb Cd

added (μg/kg of food simulant)

R% without IS (SD)a

R% with IS (SD)a

624 55 168 5.7 31−33.7 31−34.4 31−34.3 31−34.1 6−6.6 5.6−6.1 6−6.5 6−6.5

146 131 (5) 176 (24) 85 (6) 119 (7) 108 (6) 107 (7) 110 (6) 118 (4) 116 (4) 92 (8) 96 (3)

119 86 (4) 103 (9) 102 (6) 109 (2) 99 (2) 98 (4) 98 (4) 106 (2) 104 (1) 83 (6) 106 (8)

a

Three cork soaks (n = 3) were used, corresponding to each sample type (C1−C3), except for Ba and Mn (n = 2; C1 and C2) and Al (n = 1; C2).

Figure 6. Results obtained for calibration conditions.

66

Zn,

75

As, and

78

majority of producers obtain the cork material from forests in Andalusia, Extremadura, or Portugal. In this respect, it is hard to determine the precise origin of the material. It is also worth mentioning the differences between cork granules (corks 1 and 2) and cork slabs (cork 3), which may be attributed to the fabrication process applied to obtain cork granules, i.e., contamination due to the grinding process, when the cork material remains in close contact with the metallic parts of the machine for long periods of time. The amount of each element transferred from the cork sample to the food simulant solution is presented in Table 6. The results are given as micrograms of the element measured in the solution divided by the total amount of cork used for the experiment. The percentage of the element migrated from the cork to the solution is also given. As we can see, the percentages vary from 0.6% for Ba to 67% for Se. Although this last migration percentage seems quite high, some studies in the literature reported Se migration values of up to 37% from yeast in hot water (50 °C) for 24 h.24 It should be mentioned that selenoamino acids and inorganic Se (mainly selenite and selenate) are water-soluble.25 Prior to 2011, no reference values were established by the EU to determine whether these results might be considered safe. Recently, the EU has approved a new directive (EU directive 10/2011)26 establishing maximal migration values for Ba, Cu, Fe, Mn, and Zn. Additionally, because cork stoppers are considered to be a material that comes into contact with wine, the new directive recommends the use of a food simulant consisting of 20% (v/v) ethanol in water. For this reason, we have measured the amount of the element that migrates not only in a 12% ethanol/water mixture but also in a hydroalcoholic solution with 20% ethanol. The values obtained for sample C2 are listed in Table 7. As we can see, the cork samples analyzed give migration results well below the maximum established, Ba and Mn being the most critical elements with respect to the maximal concentrations allowed. It is also worth mentioning that, in general, concentrations in a hydroalcoholic solution containing 20% ethanol are slightly higher than those in 12% ethanol, which may indicate that the solubility of metallic species increases at higher ethanol concentrations. Migration Tests Using Water. Finally, we tested other conditions to perform the migration test using only water as a food simulant. In this way, we were able to avoid the presence

Se under different

cork material and the migration to wine deserve special attention. With respect to the values we found for samples C1− C3, high variability was obtained between samples, presumably depending on the provenance of the cork. Catalonia is one of the most important regions producing cork stoppers, but the 5696


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element

concentration in the food simulant (μg/kg of cork) (n = 3)

% migration

Al Ba Mn Cr Fe Ni Cu Zn As Se Cd Pb

28000 (3000) 860 (70) 3300 (200) not determined 1600 (100) 70 (30) 1400 (50) 700 (20) 41.1 (0.6) 5.4 (0.3) 4 (2) 14 (3)

3.5 0.6 10.6 not determined 1.1 10.4 28.0 0.8 6.6 67.2 10.3 3.7

37.0 (0.8) 42.3 (2) 50 (10) − − − 8 (0.3) 8.86 (0.04) 6.9 (0.8) − − −

380 (20) 350 (40) 246 (8) − 60

this work this work this work 6 22 19

Table 6. Results from the Migration Test with Sample C1 [mean (SD)]

Table 7. Migration Results Compared with Data from EU Directive 10/2011 (C2; n = 3)a

670 (60) 520 (40) 630 (40) − − −

620 (10) 23 (4) 30 (4) − − −

Cdb Nib

Asb

Seb

Pbb

ref


element

HA 12% ethanol

HA 20% ethanol

EU Directive 10/2011

Ba Cu Fe Mn Zn

0.038 (0.009) 0.052 (0.003) 0.101 (0.005) 0.30 (0.02) 0.080 (0.003)

0.37 (0.01) 0.18 (0.01) 0.43 (0.02) 0.116 (0.004) 1.0 (0.2)

1 5 48 0.6 25

660 (50) 330 (60) 710 (20) − − −

Concentration in the food simulant given in milligrams per kilogram of food simulant [mean (SD)].

Table 8. Results from the Migration Test and Different Treatments (C1; n = 3) [mean (SD)]

Milligrams per kilogram of cork. bMicrograms per kilogram of cork

83 (6) 92 (6) 1.2 (0.4) 18−9.9 −

Migration of Components from Cork Stoppers to Food: Challenges in

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