New Insights into Intrinsic and Extrinsic Factors ... - ACS Publications

Chapter 15

Downloaded by MONASH UNIV on November 25, 2015 | http://pubs.acs.org Publication Date (Web): November 24, 2015 | doi: 10.1021/bk-2015-1203.ch015

New Insights into Intrinsic and Extrinsic Factors Triggering Premature Aging in White Wines Alexandre Pons,*,1,2,3 Maria Nikolantonaki,1,2,5 Valérie Lavigne,1,2,3 Kentaro Shinoda,4 Denis Dubourdieu,2,3 and Philippe Darriet2,3 1Seguin-Moreau,

Z.I. Merpins, BP 94, 16103 Cognac, France de Bordeaux, ISVV, EA4577 Œnologie, F-33140 Villenave d’Ornon, France 3INRA, ISVV, USC 1366 Œnologie, F-33140 Villenave d’Ornon, France 4Suntory Wine International Limited, 2-3-3 Daiba, Minato-ku, Tokyo 135-8631, Japan 5Current address: Université ́ de Bourgogne, Institut Universitaire de la Vigne et du Vin, Jules Guyot, UMR A 02.102 PAM AgroSup Dijon/, F-21078 Dijon France *E-mail: [email protected]. 2Université ́

Two grape antioxidants, ascorbic acid and glutathione, and a flavan-3-ol, catechin, were analyzed and related to the production or depletion of volatile compounds (phenylacetaldehyde, methional, and sotolon) that act as markers of premature aging in dry white wines. This research assessed the impact of adding ascorbic acid (AA, 80 mg/L) and glutathione (GSH, 10 mg/L) to a Sauvignon Blanc wine sealed with two closures with different permeability to oxygen on wine flavor development over 10 years’ bottle storage. A decrease in AA was correlated with the closure’s oxygen permeability, while GSH depletion (90 % in 12 months) was associated with the dissolved oxygen content at bottling. Sensory analysis revealed significant differences in the development of wine oxidation flavors, correlated with the closure, as well as AA and GSH content. Wines spiked with AA and GSH at bottling were preferred by panelists to controls, without GSH. The sensory data were in complete agreement with analytical results,

© 2015 American Chemical Society In Advances in Wine Research; Ebeler, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

showing that these wines had the lowest sotolon content. We also demonstrated that, on the basis of analyzing the oxidation markers (sotolon, methional, and phenylacetaldehyde), high catechin levels in white wines contributed to their formation in a temperature-dependent manner.


Introduction Aging potential is one of the important features for high quality white wines. One particularity of these wines is that they conserve the flavor nuances of young wines while developing specific varietal aromas. However, this ideal aging does not occur in every wine. Premature aging is a well-known phenomenon in white wines (1–3), revealed by oxidative aroma degradation, leading to a rapid loss of their varietal qualities (4): both the formation of off-flavors and the loss of floral and fruity notes (5, 6). Prematurely-aged white wines develop several aromatic nuances reminiscent of honey, beeswax, and cooked vegetables and the volatile compounds associated with these odors have now been identified. Two of them, methional and phenylacetaldehyde, reminiscent of boiled potatoes and old rose, have detection thresholds of 0.5 and 1 µg/L, respectively, in wine model solution (7). These compounds, known as Strecker aldehydes, are formed by several pathways. The first involves the degradation of amino acids with dicarbonyl compounds (8). Generally, in wine chemistry, all dicarbonyls are potential substrates for this reaction. Indeed, phenolic compounds that have oxidized to ortho-quinones may be involved in the reactions that form these volatile compounds, via the Strecker reaction (9). This suggested mechanism has been demonstrated in synthetic solutions (10) but its contribution in wine was downplayed in a recent publication (11). Nikolantonaki and Waterhouse (12) explained this result by determining low first-order reaction rates between ortho-quinones and amino acids in a wine-like solution, thus suggesting the secondary importance of this pathway in Strecker aldehyde formation. These carbonyls have been found to be related to the wine content in combined SO2, suggesting that a significant part of the aldehydes could be present in wine under the form of SO2 adduct (13). So, these carbonyls might be released from trapped forms upon depletion of SO2 during oxidation phenomenon. The last potential precursors are alcohols, methionol and phenylethanol, who are able to be converted in there aldehydes forms via Fenton reactions during wine oxidation (13, 14). Sotolon (4,5-dimethyl-3-hydroxy-2(5)H-furanone) is a chiral volatile lactone with an intense curry odor (15). The chemical mechanism responsible for sotolon formation in wine involves oxygen, which explains the high sotolon content (100-1000 µg/L) found in wine aged under oxidation conditions, e.g.: vin jaune from the Jura (16), port, and vins doux naturels (French fortified wines) (17), which contributes to their quality and typicality. On the contrary, its presence in wines made traditionally under reductive conditions is considered an off-flavor. 230 In Advances in Wine Research; Ebeler, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


The presence of yeast lees and sulfur dioxide during barrel aging minimize the attenuation of Sauvignon Blanc varietal aromas, as well as preventing sotolon formation (15). More recently, several authors determined the contribution of sotolon to the oxidation aromas of prematurely-aged dry white wines (1, 2). The highest level measured in these dry wines was 15-20 µg/L. Chemical deamination of threonine to 2-ketobutyric acid, followed by aldol condensation with acetaldehyde, led to the formation of racemic sotolon. 2-ketobutyric acid was also identified as a product of the oxidative degradation of ascorbic acid (18). Ascorbic acid is a natural antioxidant found in small quantities in grapes. It disappears rapidly when the must first comes into contact with oxygen and during alcoholic fermentation. Wine generally does not contain any (19). Ascorbic acid was authorized many years ago as an antioxidant for wine in most countries. Its use does not raise any health-related objections. It is now used in most winegrowing countries at a maximum concentration of 150 mg/l, always in association with sulfur dioxide. The recommended concentrations are between 50 and 100 mg/l, as higher concentrations may affect wine flavor (20). The addition of ascorbic acid to prevent or delay the development of oxidative flavor in white wine continues to be a matter of debate in the literature. The advantages and disadvantages of this enological practice have been reviewed many times in the past (21, 22). Indeed, ascorbic acid is considered a powerful antioxidant which may also act as a pro-oxidant in specific cases, depending on its concentration and some physicochemical parameters (i.e. dissolved oxygen and temperature). According to several studies, the major advantage of using ascorbic acid was its rapid elimination of oxygen dissolved at bottling (23, 24) and its capacity to decrease the redox potential of wines (25). According to a study by Bauereinfeind (26), ascorbic acid addition may be favorable to wine aroma, taste, and clarity. Many years later, Peng (21), cited no protection from browning in wines containing ascorbic acid and sulfur dioxide during bottle storage. More recently, Skouroumounis (27) used sensory analysis to determine that adding ascorbic acid to Chardonnay and Riesling wines was never detrimental but could, in some cases, protect them from oxidative spoilage. As early as 1966, Ribéreau-Gayon emphasized in the Handbook of Enology that “ascorbic acid, associated with sulfur dioxide, is able to protect the wine from gentle aeration but it does not work against strong oxidation” (19). This observation was in agreement with Bradshaw (28) study, who demonstrated that ascorbic acid had a concentration-dependent pro-oxidant effect in model solution. According to our recent study, ascorbic acid under oxidative conditions was associated with sotolon formation via the formation of 2-ketobutyric acid and its reaction with acetaldehyde (18). Another natural antioxidant found in grapes but also in wines has drawn attention to researchers since the role of glutathione (GSH) has been considered in preventing must browning (29). More recently, it has been reported that this compound exerts a protective effect on certain wine aromas in Sauvignon Blanc wines (1). In this study, Lavigne showed that spiking with GSH (10 mg/L) at bottling had positive effects on wine color and varietal aroma; by preventing the degradation of varietal thiols, and sotolon formation, as well as decreasing 231 In Advances in Wine Research; Ebeler, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


the intensity of yellow color after 3 years’ bottle storage. Very recently, Herbst (30) showed that adding sulfur dioxide and glutathione slowed the decrease in 3-mercaptohexan-1-ol and 3-mercaptohexyl acetate over a 4-week period. This phenomenon was more pronounced in the case of low oxygen exposure during bottling and bottle aging (31). This behavior of thiols was recently explained in a study on the reactivity of these compounds with (+) catechin and (-) epicatechin, naturally found in white wines (32). GSH is found at high levels in young white wines compared to volatile thiols (mg/L vs. ng/L) and may act as a radical or quinone trap, thus protecting the volatile thiols. Over the past fifteen years, the influence of closures on the color and flavor of white wines has been explored in several studies, using a variety of closures and storage conditions (33–36). It is well known that the rate of ingress of oxygen into the bottle through the closure and closure-bottle interface affect the quality of aging. As recently discussed, high oxygen permeability of closures is probably responsible for the high levels of dissolved oxygen found in prematurely-aged white wines (15). The choice of wine closure type is therefore likely to have a considerable impact on the extent of wine oxidation (36). For example, Brajkovich (37), corroborated this observation, concluding that the use of screw caps stabilized the varietal flavor of Sauvignon wines (3-SH, 4-MSP) over a two-year period. Moreover, based on these results and for the reasons cited previously, we hypothesized that the ability of ascorbic acid to prevent white wine from oxidative mechanisms was associated with the closure oxygen transfer rate (OTR). The aim of this study was to investigate the effect of adding ascorbic acid, alone or with glutathione, on a Sauvignon Blanc wine, according to the oxygen permeability of two closures, based on analytical and sensory approaches. The goal of the first part of our investigation was a better understanding of the organoleptic impact of adding ascorbic acid and GSH and their influence on sotolon formation according to closure OTR. The second section focused on the impact of (+)-catechin on the oxidative evolution of white wines.

Materials and Methods Ascorbic Acid and GSH Spike in Trials In cooperation with a winery, ascorbic acid was added to a Sauvignon Blanc wine bottled on a large scale under commercial conditions at the CVBG bottling facility, using two closures with very different oxygen permeabilities. Wines were produced from Sauvignon Blanc grapes in the Bordeaux appellation during the 2003 vintage. Standard winemaking procedure for white wines was applied, avoiding all contact with wood (38). A single batch was divided between two 50 HL stainless steel vats. Free sulfur dioxide was adjusted (30 mg/L) and ascorbic acid was added (80 mg/L) to the wines in vat, two days prior to bottling. GSH was added manually to each bottle, just before filling. The overall experimental design is presented in Table 1. 750 mL green bottles were from Saint-Gobain Emballage (Cognac, France). The head space of the bottles was saturated with CO2 before sealing. Bottles were inverted for one hour after bottling. The main oenological 232 In Advances in Wine Research; Ebeler, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

parameters of the white wine are presented in Table 2. The wines were bottled at a single fill height of 10 mm, using either natural cork (Amorim, 44x24 mm, super grade) with on average, a lower oxygen permeability or a synthetic stopper (supremcorq, 36x21 mm) with tenfold higher oxygen permeability.


Table 1. Experimental Design

2003 dry white Bordeaux

Type of closure

AA addition (80 mg/L)

GSH addition (10 mg/L)

No

No

Lw-O2

Hi-O2

No

Lw-O2 AA

Hi-O2 AA

Yes

Lw-O2 AA GSH

Hi-O2 AA GSH

Yes

Cork (Low OTR)

Synthetic (High OTR)

Flavan-3-ols Spike in Trials The experiment was carried out using a Sauvignon Blanc wine from the Bordeaux area (Entre Deux Mers, 2009 vintage). The wine’s analytical parameters were as follows: pH 3.4, 12.4% alcohol (v/v), 0.3 g/L volatile acidity (eq. sulfuric acid), 3.4 g/L titratable acidity (eq. sulfuric acid), 21.0 mg/L free sulfur dioxide, 48.0 mg/L total sulfur dioxide, 7 mg/L reduced glutathione, 6.1 mg/L (+)-catechin, and 3.4 mg/L (-)-epicatechin. Wines were spiked with 50 mg/L catechin. All wines were transferred to inert vials closed with silicone septum and crimped with aluminum caps. Wines were stored in a thermostat-controlled room at 20°C or 37°C for 12 months.

Oxygen Permeability Assay This assay was performed in collaboration with LNE laboratory (Trappe, France). The methodology was consistent with ASTM D 3985 and ISO 15105-2:2003 standard applied to oxygen permeability of plastic films. Oxygen transmission rates were tested using an Oxtran 100 coulometer (Modem Controls Inc., Mineapolis). The samples were conditioned for one month to remove residual oxygen in cork cells prior to testing.

Dissolved Oxygen Assay DO was measured in 10 bottles of each condition a few minutes after bottling, using an Orbisphere 31120, according to (15). Each measurement was performed in duplicate. 233 In Advances in Wine Research; Ebeler, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

Table 2. Main Enological Parameters of the Dry Bordeaux White Wine Studied Just after Bottling Enological Parameters

Value (SD)

Ethanol (% vol.)

12.8

AV (g/L H2SO4)

0.24

pH

3.3 (0.02)

AT (g/L H2SO4)

3.2 (0.2)

free SO2 (mg/L) *

27 (1)


total SO2 (mg/L) * Ascorbic acid (mg/L)

Glutathione (mg/L) *

50 (2) *

Without

nd

With

79.8 (6.2)

Without

1.9 (0.3)

With

11.2 (0.9)

Sotolon (µg/L)

nd

Dissolved oxygen

Without AA

1.28 (0.13)

(mg/L)**

With AA

1.35 (0.18)

SD: standard deviation; nd: not detected; samples.

*

average of 3 samples;

**

average of 15

Sotolon, Phenylacetaldehyde, and Methional Analysis The content of the wines was determined, using 3-octanol as an internal standard, as previously described (15). HPLC-FLP Flavan-3-ols Analysis A Dionex Ultimate 3000 with a ternary pump (RS) and an autosampler (WPS-3000RS) were coupled to a fluorimetric detector (FLD-3100). A Chromeleon was used for acquisition, solvent delivery, and detection. Chromatograms corresponding to excitation at 275 nm and emission at 320 nm in the fluorescence detector were used to detect and quantify the various compounds (39). Separation was performed on a reversed-phase Beckman Coulter Ultrasphere ODS C18 (250 mm × 4.6 mm, 5 μm). A binary solvent was run at a flow rate of 0.7 mL/min employing (A) 5% aqueous trifluoroacetic 234 In Advances in Wine Research; Ebeler, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

acid (0.1%) and (B) acetonitrile (65%) trifluoroacetic acid (0.1%). Elution was performed with a gradient: 0-30 min from 15 to 35% solvent B, 30-35 min from 35 to 100% B. The wine injection volume was 10 µL. Each sample was injected three times. Glutathione and Ascorbic Acid Analysis The reduced glutathione was quantified as described by Lavigne (40) whereas the ascorbic acid assay was performed as described previously by Pons (18).


Sensory Analysis Approximately 30 mL wine was presented in black glasses corresponding to AFNOR (Association Française des Normes) standards. Indeed, the glasses were chosen to avoid any potential bias among the panel due to visual cues, due to the risk that wines presented in standard, clear glasses would score higher on attributes such as "oxidized". The sensory panel, which was similar throughout the experiment, consisted of 15 tasters from ISVV staff with extensive experience in white wine tasting, aged from 25 to 50. Before each session, wines from three replicates of each treatment were blended. Basic analyses (free SO2, DO) were carried out to ensure that the white wines were in a similar oxidation state. The impact of adding ascorbic acid and glutathione on wine aroma was evaluated by triangular tests in individual booths at controlled room temperature (20°C). Sensory analysis consisted of presenting three samples, two identical and one different, to a large number of judges (forced-choice method). The sensory recognition test was accompanied by a question regarding the taster’s preference. Once the tasters had determined which sample was different, they were asked to give their preference. Results of tasters who failed in the triangular test were not included in the preference test results. In our experiment, we considered that the sample was preferred when at least 80 % of the panel preferred the sample identified during the triangular test. Moreover, after 120 months, during the last sensory analysis session, the intensity of oxidized flavors in the six conditions was also assessed. Panelists scored the “oxidized” attribute on a scale of 0 to 5, where 0 indicated the wine was not oxidized and 5 corresponded to an intense oxidized flavor. Wines presenting trichloroanisole (TCA) taint were not analyzed.

Results Oxygen Permeability Assay For many years in the wine industry, closure quality was mainly assessed by its mechanical properties. Nowadays, closure oxygen permeability is considered a key factor in wine quality during storage. Many studies have investigated this process in recent years, producing different oxygen permeability data, leading to contrasting conclusions. Indeed, the oxygen permeability of a stopper is linked 235 In Advances in Wine Research; Ebeler, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


to its macroporous structure (41, 42) or the existence of a preferential cork-glass interface route for cork stoppers (43), and probably both. Direct measurements of oxygen permeability of the stopper using various methods are presented in Table 3. Several studies have determined that the steady state of diffusion is reached after 1 month storage, when the air trapped in the cork cells has been completely expulsed and consumed by the wine (44, 45). For this reason, the oxygen permeability assay was performed one month after bottling. The oxygen permeability measurements obtained in this study were similar to those found elsewhere: the synthetic stopper used was 10 times more permeable than natural cork, which had a value close to the coulometer detection limit. Consequently, oxygen permeability was probably over-estimated at 30 µL/month.

Table 3. Examples of Oxygen Permeability of Natural and Synthetic Corks from Several Studies OTR (µL/months) References

1

Natural Cork (min-max)1

Synthetic stopper (min-max)1

Personal results

30

New Insights into Intrinsic and Extrinsic Factors ... - ACS Publications

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