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Oxygen consumption by red wines. Part I: consumption rates, relationship with chemical composition and role of SO2 Vicente Ferreira, Vanesa Carrascón, Mónica Bueno, Maurizio Ugliano, and Purificación Fernandez-Zurbano J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b02988 • Publication Date (Web): 10 Dec 2015 Downloaded from http://pubs.acs.org on December 14, 2015
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1 Oxygen consumption by red wines. Part I: consumption rates, relationship with chemical composition and role of SO2 Vicente Ferreira1,2*, Vanesa Carrascon1, Mónica Bueno1, Maurizio Ugliano3, Purificación Fernandez-Zurbano2 1
Laboratory for Flavor Analysis and Enology. Instituto Agroalimentario de Aragón
(IA2). Department of Analytical Chemistry, Faculty of Sciences, Universidad de Zaragoza, 50009, Zaragoza, Spain 2 Instituto
de Ciencias de la Vid y el Vino, (Universidad de La Rioja-CSIC-Gobierno de la
Rioja), Finca La Grajera, Ctra. De Burgos Km. 6, 26007 Logroño, Spain. 3 Nomacorc
SA, Chemin Xhenorie 7, B-4890 Thimister Clermont, Belgium
* Corresponding author. Tel.: +34 976 762067; Fax: +34 976 761292. E-mail address:
[email protected] (V. Ferreira)
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Abstract
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Fifteen Spanish red wines extensively characterized in terms of SO2, color, antioxidant
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indexes, metals and polyphenols were subjected to five consecutive sensor-controlled
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cycles of air saturation at 25oC. Within each cycle O2 consumption rates cannot be
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interpreted by simple kinetic models. Plots of cumulated consumed O2 made it possible
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to define a fast and highly wine dependent initial O2 consumption rate and a second and
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less variable average O2 consumption rate which remains constant in saturations 2 to 5.
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Both rates have been satisfactorily modeled, and in both cases they were independent
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on Fe and SO2 and highly dependent on Cu levels. Average rates were also related to
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Mn, pH, Folin, protein precipitable proanthocyanidins (PPAs) and to polyphenolic
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profile. Initial rates were strong and negatively correlated to SO2 consumption,
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indicating that such initial rate is either controlled by an unknown antioxidant present
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in some wines or affected by a poor real availability of SO2. Remaining unreacted SO2 is
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proportional to initial combined SO2 and to final free acetaldehyde.
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Keywords
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Oxygen consumption rate, red wine, sulfur dioxide, polyphenols, copper, iron, radicals
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Introduction
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The central role of oxygen in the process of wine maturation has been long known 1. In
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recent years, a number of studies have described the influence of oxygen exposure on
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wine chemical and sensory characteristics, including modulation of wine aroma 2-5, color
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and mouthfeel 6-8 . As a result, it is nowadays generally accepted that moderate exposure
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of wine to oxygen can be beneficial for wine quality, while too low or too high exposure
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levels are likely to be detrimental, due to increased occurrence of reduced or oxidized
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aroma off-flavors 2, as well as low color stability and harsher mouthfeel in the case of
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insufficient oxygen exposure 6-8.
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Nevertheless, practical management of oxygen in the winery remains challenging.
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Certain steps of the winemaking process are intrinsically characterized by some degree
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of oxygen exposure, as in the case of barrel aging, micro-oxygenation and bottle
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maturation under closures allowing some oxygen ingress. However, the capacity of
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different wines to interact with oxygen is largely dependent on wine composition, so
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that the outcomes of exposing a specific wine to a given amount of oxygen are often
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unpredictable. Tools are available to deliver specific doses of oxygen during cellar and
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bottle maturation, but the lack of robust indicators helping to predict the response of a
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specific wine to oxygen exposure limits their practical application. In addition, accidental
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exposure of wine to excess oxygen remains a frequent problem in the winery, with
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consequent increased risk of oxidative spoilage.
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From a chemical point of view, when oxygen is dissolved into wine, it can rapidly react
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with phenolic compounds with an o-diphenol function under the catalytic action of
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metals such as copper and iron
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and hydrogen peroxide are formed, further propagating oxidation to various other wine
9, 10
. Highly reactive species such as quinones, radicals
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components. As a consequence, major modification in wine composition can be
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observed, including depletion of dissolved of oxygen, loss of the major wine exogenous
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antioxidant SO2, and modification in the pool of phenolic, carbonyl, and thiol compounds
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2, 9-15
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The rate of oxygen consumption has been shown to be strongly wine-dependent
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Studies in model systems indicated that wine oxygen consumption rate can depend on
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the concentration of copper and iron 11, although such correlation was not extensively
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validated in real wines, where other metal catalysts can also be present. Likewise, it was
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shown that SO2 can accelerate oxygen uptake by model wine solutions of catechin and
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epicatechin
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SO2 are systematically showing faster oxygen consumption, especially within the
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concentration ranges commonly used in modern winemaking. In addition to SO 2, wine
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contains other powerful nucleophiles that can react with oxidation products such as
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quinones. Among these, glutathione and other volatile thiols, phenolic compounds, and
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ascorbic acid can compete with SO2 for quinone scavenging, further affecting wine
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oxygen consumption rates 3, 18. High concentrations of ellagitannins and higher pH can
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also accelerate oxygen consumption by wine 10, 19.
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From a practical point of view, winemakers are mostly interested in the chemical
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transformations that are induced by oxygen consumption of the wine. Among these,
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one major concern is the progressive loss of SO2 that takes place during wine handling
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and storage in the presence of oxygen. Consumption of oxygen by the wine is indeed
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strongly correlated with SO2 loss 15, due to the ability of SO2 to recycle quinones to o-
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diphenols, directly form adducts with quinones or react with hydrogen peroxide 9, 11, 13.
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However, addition of SO2 is limited by current wine legislation, and there is a generalized
. 16, 17
.
11, 12
, but there is no definitive evidence that wines containing higher free
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consensus towards a reduction in the use of this additive, due to its potentially harmful
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effects towards health. It can be argued that, more than the actual SO 2 level, it is
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important to understand which degree of antioxidant protection SO2 can actually
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provide in the specific environment of individual wines. The question is that SO2 exists
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under different chemical forms (SO2, H2SO3, HSO3-, plus carbonyl-combined forms)
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which are in fact interconnected via different chemical equilibria. The existence of such
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equilibria makes that, at the end, all forms of SO2 contribute to its antioxidant action.
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However and since some forms are more active for one particular aspect of oxidation,
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the kinetics of the different equilibria leading to that particular form may turn relevant.
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In particular, acid-base equilibria are very fast but the interconversion between free and
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carbonyl-bonded forms is not that fast since involves the cleavage of covalent bonds.
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Therefore, oxygen-induced modification to wine components (e.g. aroma and phenolic
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compounds), are likely to be linked to the actual ability of SO2 to exert its antioxidant
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activity. To date, no study has attempted to evaluate these particular aspects of SO 2
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chemistry with regard to the ensemble of transformations taking place in a wine upon
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oxygen composition. In addition, the role of other wine components has to be also
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considered. SO2 reacts quickly with quinones 13, 20 and relatively quickly with hydrogen
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peroxide 21, so it can be argued that, for a given amount of oxygen consumed, the ability
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of a wine to form these compounds can modulate loss of SO2. Browning susceptibility of
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white wine appeared linked to wine flavanols
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concentration and free SO2 appeared to contribute to a lesser extent 22. At the same
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time, wine contains a number of other nucleophiles, including certain phenolic
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compounds, that can in theory reduce SO2 consumption by oxidation reactions
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Overall, the ability to predict SO2 loss based on compositional data would greatly assist
22-24
, while total phenolics, iron
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in rationalizing the use of SO2 as wine additive and develop strategies aimed at
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improving wine aroma stability over time. One aspect that needs to be also taken into
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account is that, in the majority of the studies hitherto published on wine oxidation the
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actual consumption of oxygen by single wines was not measured, preventing robust
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comparison of the effect of oxygen on the composition of individual wines.
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In the present study, the oxygen consumption rate of different wines has been
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measured under condition of carefully controlled oxidation, providing an initial
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evaluation of the ability of wine to combine oxygen. The chemical composition of each
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wine before and after various oxidation cycles has been thoroughly characterized,
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allowing a study of the correlations existing between initial wine composition, oxygen
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consumption rates, and oxygen-driven chemical transformations. The results provide for
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the first time a detailed insight into the factors driving the major transformations
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associated with wine oxidation.
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Materials and Methods
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Wines and oxidation process
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Fifteen Spanish red wines were purchased at a local wine store. Wines were from
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different Spanish Denominations of Origin, grape varieties and vintages as detailed in
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Table 1.
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The oxidation experiment consisted of five consecutive air-saturation cycles. The
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chemical composition of wines before and after the oxidation was extensively
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characterized. In addition, at the end of each one of the cycles, some basic parameters
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were also determined (see analyses details below). Two bottles of each wine were
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opened inside a glove chamber from Jacomex (Dagneux, France) in which oxygen in the
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gas phase was below 0.002 % (v/v). The content of 2 bottles was mixed in a beaker and
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after ensuring that dissolved O2 was non-detectable (
