Article pubs.acs.org/JAFC
Key Changes in Wine Aroma Active Compounds during Bottle Storage of Spanish Red Wines under Different Oxygen Levels Vicente Ferreira,*,† Mónica Bueno,† Ernesto Franco-Luesma,† Laura Culleré,† and Purificación Fernández-Zurbano‡ †
Laboratory for Flavor Analysis and Enology. Aragón Institute of Engineering Research (I3A). Department of Analytical Chemistry, Faculty of Sciences, University of Zaragoza, 50009 Zaragoza, Spain ‡ Instituto de Ciencias de la Vid y el Vino (CSIC, UR, GR), Department of Chemistry, Universidad of La Rioja, 260026 Logroño, La Rioja, Spain S Supporting Information *
ABSTRACT: Samples from 16 Spanish red wines have been stored for 6 months at 25 °C under different levels of oxygen (0− 56 mg/L). Amino acids, metals, and phenolic compounds were analyzed and related to the production or depletion of key oxidation- and reduction-related aroma compounds. Oxidation brings about sensory-relevant increases in Strecker aldehydes, 1octen-3-one, and vanillin. Formation of Strecker aldehydes correlates to the wine content on the corresponding amino acid precursor, Zn, and caffeic acid ethyl ester and negatively to some flavonols and anthocyanin derivatives. Formation of most carbonyls correlates to wine-combined SO2, suggesting that part of the increments are the result of the release of aldehydes forming bisulfite combinations once SO2 is oxidized. Methanethiol (MeSH) and dimethylsulfide (DMS), but not H2S levels, increase during storage. MeSH increments correlate to methionine levels and proanthocyanidins and negatively to resveratrol and aluminum. H2S, MeSH, and DMS levels all decreased with oxidation, and for the latter two, there are important effects of Mn and pH, respectively. KEYWORDS: oxidation, reduction, carbonyl compounds, methional, volatile sulfur compounds, polyphenol, metals, amino acids
■
forming often before wine browning becomes obvious.17−19 These compounds are acetaldehyde,20 methional,21 and phenylacetaldehyde.22,23 Other compounds that have also been reported as formed during wine oxidation are sotolon (4,5-dimethyl-3-hydroxy-2(5H)-furanone),24−26 (E)-2-alkenals, 2-methylpropanal, 2- and 3-methylbutanals,22 and 3-methyl-2,4nonanedione.27 Some of these aldehydes (methional, phenylacetaldehyde, 2-methylpropanal, and 2- and 3-methylbutanals) can derive from the Strecker degradation of amino acids and are in fact known as Strecker aldehydes. The direct formation from the amino acid precursors was first suggested for the case of methional.21 The mechanism suggested is a reaction of the amino acid precursor with an o-quinone produced along with oxidation, as was described in tea leaves previously,28 and as has been demonstrated to occur in synthetic solutions29 and most recently in wine-like medium.30 The extent to which this mechanism is dominant is however not clear, because the reaction rates between o-quinones and amino acids are very small in wine conditions.31 A second possibility would be the direct formation of the aldehyde from the alcohol precursor via a peroxidation mechanism,21 as demonstrated for acetaldehyde.20,32 A third possibility is the reaction of methionine with α-dicarbonyls.33 The number of processes and molecules potentially involved in the formation of those aldehydes during
INTRODUCTION Most red wines require an aging period in the bottle in order to reach their optimum quality.1,2 Two of the most relevant changes sought during such aging period are the decrease in wine astringency3−5 and the stabilization of wine color.6−8 In both cases, the rather small amounts of oxygen that the wine can take during the whole process have been shown to play a role.1,5,8 During bottle aging, wine aroma also evolves, sometimes in a negative way which causes important economic losses and image damage. In fact, 48% of wines identified as faulty in several enological contests have defects related with inadequate agingin particular with aroma-related oxidation or reduction problems.9 Therefore, there is an obvious need for a better understanding of the chemical nature of those negative aroma changes, and particularly of the role played by wine chemical composition and by oxygen on their formation. Aroma changes related to oxidation belong to two different categories: oxidation of oxygen sensitive aroma compounds and formation of new aroma active compounds by oxidation. Mercaptans are among the most sensitive to oxygen aroma compounds,10 and the oxidation of some powerful polyfunctional mercaptans has been identified as a major process determining the shelf life of specific wine types.11−14 Although those polyfunctional mercaptans do not seem to play a key role in many Spanish red wines,15 it is expected that oxidation may play a significant role on the depletion of hydrogen sulfide (H2S), methanethiol, and ethanethiol (EtSH).16 On the other hand, some aldehydes have been identified as the most important aroma compounds formed upon wine oxidation, © 2014 American Chemical Society
Received: Revised: Accepted: Published: 10015
March 31, 2014 September 11, 2014 September 12, 2014 September 12, 2014 dx.doi.org/10.1021/jf503089u | J. Agric. Food Chem. 2014, 62, 10015−10027
Journal of Agricultural and Food Chemistry
Article
Table 1. Wines Analyzed in the Experiment Including Origin, Age, Varietal Composition, and Some Basic Compositional Parameters wine
denomination of origin
vintage year
R1 R2 R3 R4 R5 R6 R8 A7 V10 C11
Rioja Rioja Rioja Rioja Rioja Rioja Rioja Arlanza Valdepusa Cariñena
2009 2010 2006 2010 2010 2009 2010 2008 2005 2007
C12
Cariñena
2005
C13
Cariñena
2010
B9 B14 B15
Campo de Borja Campo de Borja Campo de Borja
2010 2007 2010
D16
Ribera del Duero
2008
grape variety Tempranillo, Graciano, Mazuelo Tempranillo Tempranillo, Viura Tempranillo, Garnacha Tempranillo (100%) Tempranillo, Garnacha Graciano (100%) Tempranillo Cabernet Sauvignon Garnacha, Tempranillo, Cabernet Sauvignon Merlot, Tempranillo, Cabernet Sauvignon Garnacha, Tempranillo, Cabernet Sauvignon Garnacha (100%) Garnacha (100%) Garnacha (70%), Syrah (20%), Tempranillo (10%) Tempranillo (100%)
oak aging
alcohol % (v/v)
pH
TAa (g/L)
VAb (g/L)
RSc (g/L)
TPId
CIe
astringencyf (g/L)
12 0 18 0 0 18 8 12 12 18
13.20 12.50 13.00 14.00 12.50 12.60 14.20 13.00 14.20 12.90
3.57 3.60 3.42 3.98 3.67 3.64 3.53 3.69 3.66 3.56
4.60 5.29 5.04 4.52 5.01 5.10 5.56 5.49 5.23 5.59
0.44 0.20 0.51 0.45 0.44 0.59 0.44 0.60 0.60 0.86
2.09 1.52 2.23 1.77 2.32 1.67 2.31 1.98 4.35 3.81
53.30 47.40 51.20 62.40 60.30 51.50 66.60 55.60 85.80 54.60
7.75 7.98 7.88 11.79 9.55 7.18 16.92 8.45 18.34 8.63
0.21 0.14 0.20 0.26 0.36 0.25 0.15 0.33 0.87 0.47
10
13.00
3.45
5.51
0.73
3.39
78.50
11.40
0.56
0
13.00
3.61
5.23
0.57
2.57
69.80
14.52
0.31
4 15 0
13.90 13.10 13.80
3.39 3.47 3.65
5.79 5.31 5.08
0.46 0.55 0.46
3.61 4.34 2.68
74.10 62.10 61.20
13.54 10.17 12.36
0.28 0.34 0.07
18
13.60
3.63
5.18
0.48
1.71
61.70
9.57
0.45
a
Total acidity expressed in g/L of tartaric acid. bVolatile acidity expressed in g/L of acetic acid. cReducing sugars expressed in g/L. dTotal polyphenol index, expressed in absorbance × 100. eColor index, expressed as (A420 + A520 + A620) fExpressed as tannic acid.
The major aim of the present work is to search for relationships between some key chemical compositional parameters of the wines and the rates of production or depletion of oxidation- and reduction-related compounds along with bottling storage under different oxidation regimes.
wine oxidation and ultimately determining the specific aldehyde production rate of a given wine is therefore large. The list includes transition metals catalyzing the formation of quinones,34−36 amino acids, alcohols, α-dicarbonyls, wine polyphenols,32,37,38 and sulfur dioxide, known to act as antioxidant39−41 and as a carbonyl binder.42 Reduction problems are associated with the accumulation of volatile sulfur compounds (VSCs),43−45 particularly H2S and methanethiol (MeSH),14 during bottle aging in conditions of minimum oxygen ingress through the bottle closure.13,16,46−48 It is believed that the major source of VSCs in wine is yeast metabolism. The formation of small amounts of H2S are inherent to fermentation49 and related to multiple factors.50−52 The formation of MeSH and EtSH has been related to yeast catabolism of methionine and cysteine,53 although it could be also related to amino acid synthesis.54 The levels of these compounds are controlled by some treatments such as copper finning, aeration, and/or addition of lees.9,55 The reasons why these molecules accumulate during bottle aging, more often in those wines suffering of high VSCs levels during fermentation, are not clearly known,9 although several hypotheses such as the hydrolysis of thioacetates,56 the reduction of disulfides,57 the reaction between cysteine and wine α-dicarbonyls,33 the transition-metal-catalyzed reduction of sulfate or sulfite,58 or the hydrolysis of thioacetals36 were formulated long time ago. The potential role of transition metal ions in amino acid transamination, racemization, and desulfhydration is welldocumented in the classical chemistry literature,59−61 but only a recent report has shown that wines spiked with transition metals can accumulate during storage in oxygen-free containers with higher levels of H2S and MeSH.55 Therefore, the list of compounds potentially determining the wine tendency to form VSCs during wine bottle aging includes again transition metals, α-dicarbonyls, disulfides and thioacetates, sulfite and sulfate, and sulfur-containing amino acids.
■
MATERIALS AND METHODS Wines, Reagents, Standards, and Materials. Wines. Sixteen different commercial Spanish red wines from six different Spanish denominations of origin were used in the present study, as detailed in Table 1. Solvents. Dichloromethane, methanol, pentane, hexane, and diethyl ether (gas chromatography quality) were purchased from Merck (Darmstadt, Germany). Ethanol was from Panreac (Barcelona, Spain). Water with resistance of 18.2 MΩ·cm at 25 °C was purified in a Milli-Q system from Millipore (Bedford, Germany). SPE Cartridge Materials. LiChrolut EN resins (styrene/ divinylbenzene copolymer) and 1 mL internal volume polypropylene cartridges were supplied by Merck. Carboxenpolydimethylsiloxane (CAR-PDMS) fibers were supplied by Supelco (Bellefonte, PA, U.S.A.). Semiautomated solid-phase extraction was carried out with a VAC ELUT 20 station system from Varian (Wallnut Creek, CA, U.S.A.) and automated solidphase extraction was carried out with a GX-274 Liquid Handler from Gilson (Middleton, WI, U.S.A.). Chemical Standards. The chemical standards used for the analytical characterization of wines were supplied by Merck (Darmstadt, Germany), Panreac (Barcelona, Spain), Lancaster (Eastgate, U.K.), Scharlau (Barcelona, Spain), SAFC (Steinheim, Germany), Aldrich (Madrid, Spain), Fluka (Madrid, Spain), ChemService (West Chester, PA, U.S.A.) and Oxford Chemicals (Hartlepool, U.K.). Purity of chemical standards is over 95% in all cases, and most of them are over 99%. Specific details can be obtained from method references.15,62−73
10016
dx.doi.org/10.1021/jf503089u | J. Agric. Food Chem. 2014, 62, 10015−10027
Journal of Agricultural and Food Chemistry
Article
Determination of Free and Total Sulfur Dioxide. Free and total sulfur dioxide was determined following the Rippert methodology (iodometry using starch as indicator). Wine, 15 mL, was titrated with I2 0.02 N until a bluish-violet tonality appeared. These procedures are described in ref 62. Combined sulfur dioxide levels have been calculated as the difference between total and free SO2. Quantitative Analysis of Metallic Elements. Microwaveassisted digestion in a closed vessel was used to mineralize wine samples. Samples were further analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES), as described by Gonzalvez et al.64 The elements analyzed are given in Table 2.
Storage of Wine Samples under Different Oxygen Regimes. The original wine bottles were opened inside a glovebox from Jacomex (Dagneux, France) in which oxygen was under 0.002%. The content of four bottles was mixed in a big beaker and stirred until the oxygen level in the wine dropped to 0.00 mg/L (in general, initial oxygen content for the recently opened bottle was under 0.01 mg L−1), as measured with a fluorescence oxygen meter OptiOx SG-9 from Mettler Toledo (Barcelona, Spain). Then, 17 different samples of each wine (140 mL of wine with 8 mL of Argon headspace) were prepared in airtight amber vials (Aldrich Sure-Seal bottles) supplied by Sigma-Aldrich (Madrid, Spain). The vials were closed with an internal silicone septum, a strong crimp cap and an external screw cap. The internal septum of the bottles was intentionally pierced to different extents (in three bottles 0 times and in two 1, 2, 3, 4, 5, 6, and 8 times) in order to provoke different oxygen penetration rates. Vials were further sealed into plastic bags with known oxygen permeability (
