Article pp.83-92 du Vol.27 n°1 (2007)

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NOTE

Metallic profiles of Sherry wines

using inductively coupled plasma atomic emission spectrometry methods (ICP-AES)

M. Alvárez

¹

, I.M. Moreno

^*1

, S. Pichardo

¹

, A.M. Cameán

¹

, A. G. González

²

RÉSUMÉ

Profils métalliques de Sherry par ICP-AES

Douze éléments métalliques (aluminium, calcium, cuivre, fer, magnésium, man- ganèse, potassium, sodium, zinc, strontium, baryum et phosphore) ont été déter- minés par plasma à couplage inductif couplé à la spectrométrie d'émission atomique (ICP-AES), dans cent échantillons provenant de l’Appellation Jerez- Xérès-Sherry et Manzanilla-Sanlúcar de Barrameda. Ces échantillons sont traités par minéralisation humide avec H₂O₂/HNO₃ et chauffage. Les résultats montrent la normalité des distributions des éléments métalliques. L’application de la sta- tistique non paramétrique (médian, intervalle interquantil) a été étudié. Les valeurs moyennes (médians) pour ces éléments trouvées dans les échantillons sont les suivants, exprimées en mg/L : 1.66 (Al) ; 0.03 (Ba) ; 68.46 (Ca) ; 0.14 (Cu) ; 1.83 (Fe) ; 465.58 (K) ; 58.34 (Mg) ; 0.57 (Mn) ; 29.92 (Na) ; 61.27 (P) ; 0.93 (Sr) ; 0.47 (Zn). La corrélation parmi les divers éléments métalliques est donnée en utilisant la méthode non paramétrique de Spearman. La teneur des métaux dans les vins analysé est plus élevée que pour les brandies de xérès, excepté pour le Cu et le Na. En raison de cette étude des profils métalliques des vins de xérès, et en raison de sa consommation, nous pouvons proposer qu’ils apportent a minimum contribution aux limites de sécurité (par semaine) de ces éléments pour les buveurs normaux, entre 0,2 % pour le Al et 10,2 % pour le Mg.

Mots clés

métaux, Xérès, fino, vins, ICP-AES.

SUMMARY

Twelve elements, namely alumnium, calcium, copper, iron, magnesium, manganese, potassium, sodium, zinc, stroncium, barium and phosphorous were deter-

1. Departamento de Bioquímica – Bromatología – Toxicología y Medicina Legal – Facultad de Farmacia – Calle Profesor García González, nº 2 – 41012 Sevilla – Spain.

2. Departamento de Química Analítica – Facultad de Química – Calle Profesor García González, nº 1 – 41012 Sevilla, Spain.

* Correspondence: Tel. 00 34 954 55 67 62 – Fax: 00 34 954 23 37 65 – email: [email protected] – Facultad de Farmacia – Calle Profesor García González, nº 2 – 41012 Sevilla – Spain.

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mined in one hundred samples from Jerez-Xérès-Sherry & Manzanilla-Sanlúcar de Barrameda Appellations by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The procedure involved the digestion of the sherry samples by H₂O₂/HNO₃ treatment and heating. The results obtained showed that metal data sets were non normally distributed and accordingly, non parametric statistics (median, interquartil range) are needed. The average levels (medians) of these elements found in the samples are as follows, in mg/L: 1.66 (Al); 0.03 (Ba); 68.46 (Ca); 0.14 (Cu); 1.83 (Fe); 465.58 (K); 58.34 (Mg); 0.57 (Mn);

29.92 (Na); 61.27 (P); 0.93 (Sr); 0.47 (Zn). The interrelation of metal couples was studied through the Spearman non-parametric sample correlation. The content of these metals was higher than in Sherry brandies, with the exception of Cu and Na. As a result of this study of the metallic profiles of Sherry wines and due to its consumption, we can suggest that they make a minor contribution to the safety intake limits (per week). Actually they range between 0.2% in Al and 10.2% for Mg, for normal drinkers.

Keywords

metal, sherry, fino, wine, ICP-AES.

1 – INTRODUCTION

Data on the mineral content in wines have been extensively studied and reported due to their implications in organoleptic, hygienic and nutritional characteristics as well as their toxicological implications (JOS et al., 2004). Metals can affect the entire wine-making process, from vine growing to the fermentation and aging of wine, mainly through their influence on the organoleptic properties of the finished product (LÓPEZ-ARTIGUEZ, et al., 1996). It is known that certain metal ions, such as Fe, Cu and Mn which participate significantly in the oxidative evolution (browning process), being these metals the activators of this process (BENITEZ et al., 2002) where the oxygen is the initiator and polyphenols oxidizable maters. The metal content of the wines can be influenced by factors such as the levels of these elements in soil, ferti- lising practices and processing conditions (MAARSE, et al., 1987).

Determination of the concentration of metallic elements in wine also allows cal- culation of the daily intake of such elements from the wine. Several studies (DARRET et al., 1986) reveal that wine is an important source of iron. The ratio of potassium/

sodium in wines is of interest in nutritional studies concerning the effect to diet on hypertension. Magnesium and aluminium in excess could be toxic to persons with kidney disfunction, which prevents adequate elimination of these elements (LÓPEZ- ARTIGUEZ et al., 1996).

« Fino » is a type of sherry wine produced according to the formely named

« Criaderas and Soleras » method used to blend the different vintages (http://

www.sherry.org/sherry.htm). This kind of wine can only be made in some historical wine regions located in the south of Spain where they have their own regulations for denomination (D.O.).

In reference to these growing areas, the production region of the wines protected by the Jerez, Xèrès, Sherry Manzanilla-Sanlúcar de Barrameda Appellation is located in the southern of Spain. The Appellation includes the cities of Jerez de la Frontera, El Puerto de Santa María and Sanlúcar de Barrameda. Jerez-Xérès-Sherry

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& Manzanilla-Sanlúcar de Barrameda Appellations uses grapes belonging to the Pal- omino-Fino variety mainly. Typical vineyard soil is « albariza », rich in limestone and clay which conjugates both permeability and high retention of water. This later fea- ture is essential for these lands where dry seasons are expected. The climate of this zone is warm with dry summers (25ºC), where winds coming from Atlantic Ocean and humidity owing to closeness to the sea play an important role (http://

www.sherry.org). The secret of the fino wine is the combination of soil, the damp climate which encourages the growth of the `flor´ (a coat of yeast belonging to the genus Saccharomyces that isolates the wine from the air and prevents its oxidation) and the solera and criaderas system used to blend the different vintages.

« Manzanilla » is made exclusively in Sanlúcar de Barameda. The higher humidity allows the `flor´ to flourish year round whereas in Jerez and El Puerto de Santa Maria, the yeast dies down with arrival of hot dry weather.

The human consumption in Spain of wine such including wines with Appellations has increased by about 5% per year (MAPA, 2005). Daily consumption of wine in moderate quantities contributes significantly to the requirements of the human organism for essential elements such as K, Ca, Mg, M, Zn, but at the same time as modern societies appear to consume large amounts of wine, the daily intake of heavy metals could be above the maximum acceptable limits established (LARA et al., 2005) Therefore, a knowledge of the metal content in these beverages may serve as indicator of possible toxic exposure for high consumers. The aim of the present paper is to determine the metal content of finos coming from Jerez-Xérès-Sherry &

Manzanilla-Sanlúcar de Barrameda region in order to characterise them and to eval- uate human exposure. Metals were determined by using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) as it is described in the experi- mental section.

2 – MATERIALS AND METHODS

2.1 Apparatus

Elemental analyses were carried out on a A Fison-ARL 3410 Inductively Coupled Plasma Atomic Emission Spectrometer (Fisons Instruments, Valencia, CA). Table 1 shows the analytical lines used for each element, as well as the instrumental conditions.

2.2 Reagents and solutions

Merck (Darmstadt, Germany) CertiPUR^® ICP-multielement standard solutions of about 1000 mg/L were used as stock solution for calibration. A mixture of 15 mL hydrogen peroxide (Merck, 110 v/v) and 1 mL nitric acid (Merck, analytical grade, 65% w/w, density of 1.40 Kg/L and maximal content impurities as follows:

0.000001% Cu, Mn, Sr, Ba; 0.000005% Al, Zn; 0.00001% K, Mg; 0.00002% Fe;

0.00005% Ca, Na) was used for the mineralization of samples. Distilled, deionised water (Milli-Q Water System, Millipore Corporation, Bedford, MA) was used through- out. The laboratory glassware were kept in a 5% in solution of nitric acid overnight, the washed deionised water, and dried in a dust-free atmosphere in order to prevent metal contamination.

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Table 1

ICP-AES Operating Conditions.

Table 1

Conditions opératoires pour l’ICP-AES.

2.3 Samples

One hundred samples of different brands were processed (fifty finos from Jerez and fifty manzanillas from Sanlucar de Barrameda). Wines bottles were purchased in liquor retails and markets. The alcoholic content ranged from 15 to 18% v/v ethanol for all kind of wine samples. Each sample was identified with a sample number.

Once opened, wine samples were submitted to the following digestion procedure: 25 mL of wines with 15 mL of hydrogen peroxide are heated at 80°C until a volume of about 20 mL. Then, 1 mL of nitric acid is added, and the heating is contin- ued until a final volume of about 2 mL. This volume is mixed with milli-Q treated water up to the starting volume. Three replicated digestions were made for each sample. Three blanks were prepared in an identical way, but omitting the sample.

The average of blank ICP-AES signals was substracted from analytical signals of samples before interpolation on calibration graphs. The repeatability of the method was tested in a former recovery study involving spiked samples of five wines. Metals were added to sample at about 25%. Analyses of original and spiked wines were made in triplicate. Repeatability values for the different metals ranged within 0.4- 0.8% RSD.

Parameter RF frequency

Operating Power Coolant Ar flow^-1 Plasma Ar flow^-1 Carrier Ar flow^-1 Torch type Nebulizer type Sample flow rate^-1 Detection wavelengths (nm) Al

Ba Ca Fe K Mg Mn Na P Sr Zn Cu

27.12 MHz 650 W 7.5 L min^-1 0.8 L min^-1 0.8 L min^-1 minitorch Meinhard 2.3 ml min^-1

396.152 455.403 393.366 259.940 766.490 279.553 257.610 589.592 214.914 407.771 213.856 324.754

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3 – RESULTS

In order to characterise the studied wine samples, statistics on centralization and dispersion features were calculated.

Distribution of elements in wines from Jerez-Xérès-Sherry & Manzanilla- Sanlúcar de Barrameda Appellations.

Table 2 summarises the metal concentration values in the 100 samples of wines from this Appellations, as well as arithmetical and geometrical means, ranges and lower/upper quartiles. All results were expressed in mg/L and are the average of triplicate measurements.

Table 2

Metal concentration in fino and manzanilla wines from Jerez-Xérès-Sherry & Manzanilla- Sanlúcar de Barrameda Appellations (mg L^-1).

Table 2

Niveaux métalliques pour les vins de fino et Manzanilla issus des appellations Jerez- Xérès-Sherry & Manzanilla-Sanlúcar de Barrameda (mg L^-1).

The distribution of the metal ions in the wine samples were tested for normality according to some typical assays, such as the Lilliefors (LILLIEFORS, 1967), Shapiro- Wilk (SHAPIRO et al., 1968) and Kolmogorov Smirnov (KOLMOGOROV, 1941) tests. As none of the chosen metals were normally distributed, all further statistical computa- tions were based on non-parametric techniques. The Box-whisker plots shows at a glance the spread and symmetry of the data distribution. Thus, for the sake of visu- alization, the corresponding Box-whisker plots for the studied metals are displayed in figure 1.

n Mean ± SD Median Range Lower

quartile

Upper quartile

Al 100 1.64 ± 0.54 1.66 0.59-3.51 1.28 1.98

Ba 100 0.05 ± 0.09 0.03 0.01-0.74 0.02 0.04

Ca 100 68.67 ± 11.54 68.46 32.89-105.93 61.35 74.43

Cu 100 0.26 ± 0.34 0.14 0.02-1.63 0.07 0.32

Fe 100 1.78 ± 0.61 1.83 0.69-3.55 1.40 2.26

K 100 479.86 ± 122.83 465.58 210.40-850.58 401.88 535.17

Mg 100 59.32 ± 11.99 58.34 32.91-104.59 52.86 63.79

Mn 100 0.57 ± 0.24 0.57 0.13-1.21 0.38 0.77

Na 100 31.50 ± 6.55 29.92 20.52-56.49 27.01 34.11

P 100 63.75 ± 14.64 61.27 39.56-129.55 55.41 67.11

Sr 100 0.90 ± 0.26 0.93 0.17-1.37 0.79 1.08

Zn 100 0.50 ± 0.38 0.47 0.04-1.89 0.21 0.60

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3.1 Study of metal correlation

A correlation analysis was performed in order to find out the possible interrela- tions among metal concentrations in Sherry wine. The non-parametric technique of Spearman (MILLER and MILLER, 2000) was applied. The most important correlations (with a probability (P) of error level less than 0.001) with a Spearman coefficient R ≥ 0.6, correspond to the couples Zn/Mn; Zn/Cu; P/Mg; Mn/Fe. Although typical linear correlations are inappropiate due to the non normality of the distribution of these metals, from a pictorial viewpoint these correlations can be observed in figure 2.

ZN NA

CA MG P

140 120 100 80 60 40 20 0

2,2 1,8 1,4 1,0 0,6 0,2 – 0,2

3,8 3,2 2,6 2,0 1,4 0,8 0,2 900 800 700 600 500 400 300 200 100

0,12 0,10 0,08 0,08 0,04 0,02 0,00

MN CU SR

BA AL

FE

K

Figure 1

Box and whisker plots of the different metals (aluminium, calcium, copper, iron, magnesium, manganese, potassium, sodium, zinc, stroncium, barium

and phosphorous) (mg L^-1) in wine samples.

Figure 1

Histogrammes (Box et Whisker) pour les différents métaux (aluminium, calcium, cuivre, fer, magnésium, manganèse, potassium, sodium, zinc, strontium, baryum et phosphore)

(mg L^-1) dans les échantillons de vin.

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0 0,2 0,4 0,6 0,8 1 1,2 1,4

0 0,5 1 1,52 2

0 0,5 1 1,52

0 50 100 150

0 0,5 1 1,5

2 Mn (mg/L)Cu (mg/L)Mg (mg/L)Fe (mg/L)

0 0,5 1 1,5 2

0 20 40 60 80 100 120

0 1 2 3 4

Zn (mg/L)

P (mg/L)

Mn (mg/L)

Figure 2

Interrelation between the metals Zn, Mn, Cu, and Fe in Sherry wines.

Figure 2

Corrélations entre les éléments Zn, Mn, Cu et Fe dans les vins de Xérès.

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4 – DISCUSSION AND CONCLUSIONS

According to the content found, metals could be classified in two categories: the main group including K, P, Ca, Mg, Na, and, the minority set consisting of Fe, Al, Sr, Zn, Mn, Cu and Ba. Potassium exhibit higher concentrations (465.58 mg/L average level)than the rest of the elements, P, Mg and Ca presented lower and similar contents, their average values were respectively 61.27 mg/L, 58.34 mg/L and 68.46 mg/L. Sodium was also present with values higher than 30 mg/L. The remainder metals mostly appeared with values close to 1 mg/L, such as Fe and Al, and even lower, Zn, Mn, Cu, Sr, being Ba the metal with the lowest concentration. There is a small amount of data about the metal content in Sherry wines which has been previ- ously reported in the literature. In comparison with the contents of Fe, Cu and Mn in sherry wines reported by BENITEZ et al., (2002) our results present higher range of values for Cu (0.359-0.014 mg/L), similar range for Mn (1.29-0.111 mg/L) and lower levels for Fe (6.07-0.830 mg/L). Mean of zinc levels were higher in comparison with other wines from south-eastern Spain (TERRES et al., 2001).

The occurrence of the studied metals may be explained from many different sources. All of them could be on the soil influence in major or minor extent, espe- cially for phosphorous, magnesium and iron. Besides, agricultural practices such as the use of zinc-containing pesticides, or copper-based vineyards sprays play also a primary role (SCOLLARY, 1997). The last but no the least, the nature of the wine elab- oration is another source of metal presence. In some cases, blends with foreign musts in order to balance the wine production may lead to increasing of iron content that should be suitably controlled. Metal containers used during ageing stages and the technology process with materials containing metals during wine production;

also contribute in cases of iron, zinc or aluminium (LARA et al., 2005).

Compared with the metallic profile of Sherry brandies (CAMEÁN et al., 2000), Sherry wines exhibit higher contents for all the metals analysed with the exception of Cu and Na. This fact can be explained by considering the metallic nature of alem- bics (alquitaras) employed in the distillation step of brandy production, because Cu could migrate into the beverage; Na could be incorporated into the brandy during maturation in oak casks. According to some authors (TERRES et al., 2001) Zinc levels in distilled beverages were significantly lower than levels found in fermented ones (wine and beer) because zinc transfer from the grape is facilitated during the manu- facturing of fermented drinks and also, the separation of alcohol by volatility in distilled ones, does not facilitate this transfer.

Finally, in order to alow some discussion about the metal intake trough sherry wines consumption, an average intake of each element/person/week was evaluated from our results by considering the estimated wines in general consumption in Spain and the mean content of the corresponding element. Since data on sherry wine consumption is unavailable, 36.4 L/person/year is the official ratio consumption of wines in general for our country, established by the Spanish Ministry of Agriculture and Fish (MAPA, 2005).Comparisons were performed with some safety limits for the studied metals, such as the Provisional Tolerable Weekly Intake (PTWI), Estimated Safe and Adequate Daily Dietary Intake (ESADDI), etc., when available. For the sake of homoge- inity, indices were scaled to mg of the element/person/week and are displayed in table 3. Average consumption of Sherry wines does not significantly expose the drinker to un-safe levels of the metals studied. In fact, this consumption could represent the following percentages in the safety limits (SL) established for all the elements (0.2% in Al;

4.8% in Ca; 0.7% in Cu; 1.3% in Fe; 1.5% in K; 10.2% in Mg; 3.5% in P; 2.2% in Zn).

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Moreover, in comparison with the recommended daily allowance (RDA) established by U.S.RDA (1985), for some elements such as Cu (2mg), Fe (18mg) and Zn (15mg), the corresponding quantities of those are very low in normal drinkers: 0.014 mg/day; 0.18 mg/day and 0.047 mg/day, respectively (http://www.nutrientfacts.com).

Table 3

Comparison between the estimated averaged metal intake (EAMI) through sherry wines consumption and safety limits (SL) (mg/person/week).

Table 3

Comparaison des valeurs pour l’estimation d’ingestion métallique (EAMI) lours de la consommation des vins de Xères et les limites de sécurité (SL) (mg/personne/semaine).

Element EAMI (mg/person/week)

SL

(mg/person/week) References

Al 1.16 490 ELLENHORN, 1997

Ba 0.02 –

Ca 47.92 1000 HERNÁNDEZ and SASTRE, 1999

Cu 0.098 14-21 ELLENHORN, 1997

Fe 1.28 9800 ELLENHORN and BARCELOUX, 1988

K 325.90 21840 ELLENHORN and BARCELOUX, 1988

Mg 40.83 400 HERNÁNDEZ and SASTRE, 1999

Mn 0.40 –

Na 20.94 –

P 42.90 1200 HERNÁNDEZ and SASTRE, 1999

Sr 0.65 –

Zn 0.33 15 HERNÁNDEZ and SASTRE, 1999

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