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Effect of wood aging on wine mineral composition and 87Sr/86Sr isotopic ratio Ayse Deniz Kaya, Raúl Bruno de Sousa, António Sérgio CurveloGarcia, Jorge Manuel Ricardo-da-Silva, and Sofia Catarino J. Agric. Food Chem., Just Accepted Manuscript • Publication Date (Web): 22 May 2017 Downloaded from http://pubs.acs.org on May 24, 2017

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Journal of Agricultural and Food Chemistry

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Effect of wood aging on wine mineral composition and 87Sr/86Sr isotopic ratio

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Ayse Kaya1, Raúl Bruno de Sousa1, António S. Curvelo-Garcia2, Jorge M. Ricardo-da-Silva1,

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Sofia Catarino1,2,3*

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1

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017, Lisboa, Portugal

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Instituto Nacional de Investigação Agrária e Veterinária, 2565-191 Dois Portos, Portugal

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CEFEMA, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-

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001 Lisboa, Portugal

LEAF, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-

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*Corresponding author: [email protected]; +351 21 3653246

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ACS Paragon Plus Environment


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Abstract

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Evolution of mineral composition and wine strontium isotopic ratio 87Sr/86Sr (Sr IR) during

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wood aging were investigated. A red wine was aged in stainless steel tanks with French oak

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staves (Quercus sessiliflora Salisb.), with three industrial scale replicates. Sampling was

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carried out after 30, 60 and 90 days of aging, and the wines evaluated in terms of general

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analysis, phenolic composition, total polysaccharides, multi-element composition and Sr IR.

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Li, Be, Mg, Al, Sc, Ti, V, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Mo, Sb, Cs, Ba, Pr,

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Nd, Sm, Eu, Dy, Ho, Er, Yb, Lu, Tl, Pb elements and 87Sr/86Sr were determined by

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quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS), Na, K, Ca and Fe by

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flame atomic absorption spectrometry (FAAS). Two-way ANOVA was applied to assess

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wood aging and time effect on Sr IR and mineral composition. Wood aging resulted in

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significantly higher concentrations of Mg, V, Co, Ni and Sr. In the end of aging period, wine

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exhibited statistically identical Sr IR compared to control. Study suggests that wood aging

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does not impact 87Sr/86Sr, not precluding the use of this parameter for wine traceability

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purposes.

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Key words: wine, authenticity, wood aging, strontium isotopic ratio 87Sr/86Sr, mineral

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composition

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Introduction

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A large number of studies indicates that mineral composition and concentration of wine can

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give information about their geological origin and multi-elemental analyses can determine the

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wine fingerprint. 1-3 By means of statistical techniques, discrimination of elements according

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to the products’ geographical area where they are grown is obtained. However, mineral

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composition of rock and soils changes from one region to another and also with different

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agricultural applications, such as fungicide, pesticide and fertilization applications,

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winemaking practices and environmental conditions. 4 - 8

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Heavy elements’ isotopic ratios can give information about the plant’s origin. In order to

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establish a reliable tool for geographical origin determination of wines, the selected

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abundance ratio of the element must not be altered by the agricultural and winemaking

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practices through the chain from vineyard to bottle, in other words the wines must reflect the

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same ratios as in the soil or in the rocks where the vines are grown. 2 It is also important to

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take into consideration anthropogenic human factors such as irrigation water, pollution and

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fertilizers that can contribute as mineral sources to the plants. 9

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Analytical techniques of ICP-MS and Thermal Ionization Mass Spectrometry (TIMS) can

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quantify heavy isotopes by spectroscopic methods. Recently, a high number of studies have

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been published with especially ICP-MS technique for characterizing the mineral composition

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of wines and correlating them with their geographical origin. 2,4 - 14

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Moreover, Sr IR values of the substratum and affiliated grapes and wines exhibit correlated

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results with each other. 3, 15

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Being of element of interest of this study, strontium occurs in the Nature as four isotopes.

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Three of them are stable (84Sr, 86Sr and 88Sr) with constant values which means they are non-

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radiogenic while 87Sr is radiogenic and is derived from radioactive β-decay of 87Rb and

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absolute amounts of the stable 86Sr remains constant. 8 Hence, Sr IR of a rock, depending on



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its age and content of Rb, gives particular data on different geological regions. Horn’s team

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stated that soils of respective vineyards regions have different 87Sr/86Sr ratios. The elements,

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which are absorbed by plants, maintain the same isotopic ratios as in the soil and rocks. The

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team used thermal ionisation mass spectrometry (TIMS) method for Sr isotopic ratio

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measurement. This technique gives both accurate and precise results. 8 However, being

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expensive and an inconvenient method with long sample preparation, the technique is less

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favored and unfeasible. Thanks to its fast and simpler sample preparation, low sample

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analysis cost, ICP-MS method has recently been used for isotope ratio determination.

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Lately, there are many researches that focus on the wine authenticity tools, especially by

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using 87Sr/86Sr ratios, associating the wines with their vineyards. Many studies suggest Sr IR

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as one of the most reliable fingerprint tools when it comes to relating the plants to the soil. 3,

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15- 22

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Almeida and Vasconcelos (2004) stated that although winemaking processes, chemical

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applications in the vineyard change the elemental composition of must and wine, a strong

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correlation in terms of Sr IR between wine and grape juice is still found. A similar study also

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reports that the analytical results of red and white wines did not show significant differences

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between oenological food chains. 18 Sr isotopic values of red and white wines were not

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affected by addition of fining agents (yeast and bentonite) during winemaking process

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proving the close relation with the vineyard. One recent study by Durante et al. (2016) that

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shed light on the use of Sr IR as geographical tracer, investigated the cellar practices that used

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different additives, such as clarification or deacidification agents as well as concentrated

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musts. The objective in the study was to see whether the 87Sr/86Sr ratio of wine is affected by

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these practices. Considering constancy of Sr IR from the soil to the plant and eventually into

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the wine, samples from grape juice, intermediate products and wine were taken at each step.


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In the end, 87Sr/86Sr ratio was not altered and suggested to be a powerful tool to discriminate

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the wines based on their region. 20

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A very recent study from Moreira et al. (2017) investigated also the effect of nanofiltration

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(NF) on the Sr IR. It was confirmed that there was no significance on 87Sr/86Sr ratio of wines.

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In addition to Sr IR data, the use of combined analytical parameters can provide increasingly

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robust results for the identification of geographical origin to have complementary information

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for authentication purpose of wine by means of relation between its chemical compositions

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and the territory where the grapes grow. 24 For instance, 87Sr/86Sr values along with Mg

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concentrations were best discriminator minerals of wine origin. 25

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One study in Australia also justifies the robustness of the strontium isotopic ratio method in

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order to differentiate between Australian wines’ and Non-Australian wines. Nevertheless,

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overlap of strontium isotopic ratio from different countries was observed. This suggests that

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the use of only one fingerprinting method may not be sufficient. 14

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As commonly described in the literature, aging in wood highly contributes to improve the

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sensory characteristics of wine by means of extracted compounds from the oak into the wine.

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These extracted compounds are dependent upon wine composition, oak wood composition

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and the time that wine is in contact with wood. 26 Oxidation, copigmentation, polymerization

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and condensation phenomena occur during wine and oak contact time that ensure the stability

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and improve the wine’s taste by reducing its astringency. 27

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It is emphasized by many authors that the technological processes and contact of wine with

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vineyard equipment can increase metal concentrations during maturation and aging. 5, 6, 28 - 31

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In spite of several studies indicating that 87Sr/86Sr isotopic ratio remains stable after

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winemaking processes, the literature lacks the information on the wood aging influence on

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mineral composition and wine Sr IR. The main aim of this study was to uncover the impact of



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wood aging by oak staves on strontium composition whether they change the Sr composition

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or 87Sr/86Sr isotopic ratio during aging of red wines and shed some light also to the metal

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extraction from wood to wine.

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Therefore, a red wine was aged in stainless steel vats (industrial scale) with oak wood

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(Quercus sessiliflora Salisb.) staves, in triplicate. The wines were sampled once at time-zero

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and after 30, 60 and 90 days of aging and evaluated in terms of general analysis, total

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polysaccharides, total anthocyanins, total phenols index, multi-element composition and

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Sr/86Sr isotopic ratio.

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Materials and Methods

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Wines and Wood Material

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A red wine of Castelão grape variety (Vitis vinifera L.) from 2014 vintage from a winery in

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Península de Setúbal region of Palmela DO was aged with French oak (Quercus sessiliflora

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Salisb.) staves in stainless steel vats with the volume of 34.000 L during 90 days. The

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experiment was carried out in industrial scale in the cellars of the winery. The wines did not

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suffer any stabilization treatment before aging in wood.

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The physical-chemical characteristics of wine before starting aging were: alcoholic strength

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13.6 % vol.; total acidity 5.40 g/L (expressed in tartaric acid); volatile acidity 0.7 g/L

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(expressed in acetic acid); pH 3.62; free sulphur dioxide 14 mg/L; total sulphur dioxide 45

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mg/L with completed malolactic fermentation.

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Experimental Conditions / Experimental Design

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Three stainless steel vats (34,000 L) have been added medium plus toasted (< 200 °C) oak

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staves in dimensions of 91 cm x 6.4 cm x 0.95 cm made from French oak (Quercus

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sessiliflora Salisb.) in February, 2016. Typical drying time of oak wood was 18-24 months.


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One oak piece was added per 40 L of wine with the surface to volume ratio of 33.75 cm2/L.

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Micro-oxygenation was applied with the amount of 3 mg O2/L per month. Storing

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temperature of tanks was close to 18 °C. The experiment period of 90 days is representative

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of that applied in industry for wine aging with oak wood staves and micro-oxygenation.

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Sampling of the wines was performed each month. It is worth to note that stave dimensions

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and micro-oxygenation amount were decided by the winery according to their experiences.

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The experiment was carried out as one control vat, without oak staves which is designated as

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Control and three identical vats (triplicates) with oak staves that are designated as Wood.

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General Physical and Chemical Analysis

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Physical and chemical analysis and determinations was carried out by using OIV

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(International Organization of Vine and Wine) analytical methods. 32 Alcoholic strength by

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distillation and determination by hydrometry, free and total SO2 by titration with iodine,

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volatile acidity by distillation followed by acid-base titrimetry, density by aerometry, total dry

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extract by calculation, pH value by potenciometry, total acidity by acid-base titrimetry,

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malolactic fermentation verification by paper ascending chromatography, reducing

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substances, chromatic characteristics; total anthocyanins and total phenolics index by

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spectrophotometry and ash determination. Total polysaccharides content in wine was

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determined by an adopted method which was established by Segarra et al. (1995). 33 In this

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method, settling the wine samples that are diluted with ethanol (96% vol.) about 12 - 14 hours

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in order to eliminate the phenolic and other compounds, and then washing the precipitation

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were important steps for the determination. All the analyses were carried out in duplicate,

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with exception of total polysaccharides performed in triplicate, due to the low precision of the

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method.

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Phenolic Composition and Chromatic Characteristics

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The chromatic characteristics of wines (tonality and color intensity) were measured in the

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framework of OIV standards. 32 Total phenols and total anthocyanins concentrations were

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assessed by the methods established by Somers and Evans (1977): the first by measuring the

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absorbance at 280 nm and correcting for absorving non-phenolics; total anthocyanins based

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on their responses to pH change and to sulphur dioxide addition. 34

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Mineral Composition

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The wine samples were analyzed in terms of their Na, K, Ca and Fe content by flame atomic

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absorption spectrophotometry methods described by OIV. 32 The equipment Perkin Elmer,

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Analyst 100, equipped with an air-acetylene burner and appropriate hollow cathode lamps,

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was used.

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Following elements were determined by quadrupole inductively coupled plasma mass

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spectrometry (Q-ICP-MS) semi-quantitative methodology described in the study of Catarino

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et al. (2006): Li, Be, Mg, Al, Sc, Ti, V, Mn, Co, Ni, Cu, Zn, Ga, As, Rb, Sr, Y, Sb, Cs, Ba, Pr,

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Nd, Eu, Dy, Ho, Er, Yb, Lu, Tl and Pb. 35 A Perkin-Elmer SCIEX Elan 9000 (Norwalk, CT,

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USA) was utilized with Gilson pump and a Scott-type spray chamber, a crossflow nebulizer

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and nickel cones.

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In order to optimize operational conditions, monoelement standard solutions of Be, Co and in

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1000 mg/L (Merck) and a multi-element solution with Mg, Cu, Rh, Cd, In, Ba, Ce, Pb and U

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10 µg/L (Perkin-Elmer) were used. Wash, blank and standard solutions were prepared with

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ultrapure concentrated HNO3 Ultrex II 70% (v/v) (J.T. Baker). Analytical calibration was

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established with a standard solution with 30 elements, 10 mg/L (Perkin-Elmer). Standard

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solutions of Rh and Re 1000 mg/L (Merck) were used for internal standardization.

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Strontium Isotopic Ratio Analysis

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Sample Preparation

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Prior to 87Sr/86Sr determination by Q-ICP-MS, following three main analytical steps in

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sequence were performed as described by Martins et al. (2014): sample digestion by High

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Pressure Microwave Digestion (HPMW) (1), chromatographic separation of 87Sr and 87Rb (2)

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and determination of Sr and Rb content by Q-ICP-MS (3). 3

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(1) For elimination of organic substances in order to prevent any interference during

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chromatographic separation, the wine was digested by High Pressure Microwave Digestion

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(HPMW, Milestone ETHOS Plus Microwave Labstation). 36

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(2) Separation of Sr from Rb is an essential step for correct determination due to isobaric

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overlapping 87Rb and 87Sr. An HIPEX Duran column was filled up by using Dowex 50W-

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X8/400 (Sigma-Aldrich) mesh resin and EDTA as eluent. Separation consists of four phases

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which are resin activation/pre-treatment; resin conditioning; sample preparation/dilution and

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elution. 3 Separation was done in duplicates.

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(3) Sr and Rb total content and 87Sr/86Sr isotopic ratio were measured by the ICP-MS

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equipment previously described. After first two steps, Sr containing fraction was used for Q-

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ICP-MS analysis. Determination of Sr and Rb total contents in Sr-containing fractions

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previously to the isotopic measurement is important in order to keep Rb concentration less

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than 1% of the Sr content in Sr-fraction. The SRM 987 (SrCO3) from National Institute of

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Standards and Technology (NIST) was used as an isotopic reference material for correction of

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mass bias phenomenon. 3 Analytical steps for Sr and Rb separation and isotopic ratio

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determination are summarized in Figure 1.

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87

Sr/86Sr Isotopic Ratio Determination



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After separation of Rb and Sr by ion-exchange chromatography, analytical determinations of

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Rb and Sr concentration and 87Sr/86Sr were carried out by ICP-MS using the Perkin-Elmer

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SCIEX 9000 ICP-MS equipment before mentioned. In Figure 1, it is illustrated. Detailed

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analytical protocol is in the study of Martins et al. (2014). 3

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Statistical Analysis

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The two-way analysis of variance (ANOVA) was performed to evaluate the effects of wood

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aging and aging time on the studied wines. Significant differences were compared with

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posthoc LSD (Tukey’s test) by using Statistica 7 software (StatSoft, Inc. 2004). p- values that

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are lower than 0.05 were considered to be significant (p

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