Occurrence of Brettanomyces/Dekkera in Brazilian red wines and its correlation with ethylphenols

Occurrence of Brettanomyces/Dekkera in Brazilian red wines and its correlation with ethylphenols

Larissa Dias de Ávila^I; Marco Antônio Záchia AyubII, ^*

^IInstituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Sul, Bento Gonçalves, RS, Brazil

^IIInstituto de Tecnologia e Ciência de Alimentos, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil

ABSTRACT

The yeast Brettanomyces/Dekkeracan cause important spoilage in wines, with the production of ethylphenols and other off-flavor compounds. This study aimed at determining the presence of this yeast and the ethylphenols produced by them in Brazilian red wines, establishing their relationship with other chemical characteristics. Isolates of Brettanomyces/Dekkerawere quantified by plating 126 samples of dry red wine in selective culture medium, while ethylphenols were analyzed by solid phase extraction and GC/FID. Free and total SO₂, alcohol, total dry extract, residual sugar, total and volatile acidity, and pH were also determined. Brettanomyces/Dekkerawas present in 27% of samples. Ethylphenols were detected in most samples, with amounts higher than the threshold limit of 426 mg/L found in 46.03% of samples. The majority of wine samples showed inadequate levels of SO₂and residual sugars, facts that might facilitate microbial spoilage. The passage in barrels and the grape varieties (Cabernet Sauvignon and Merlot), did not show any influence on the levels of contamination or ethylphenols contents. The prevalence of Brettanomyces/Dekkeraand the concentrations of ethylphenols were high considering the sensory impact they can cause. The growth of Brettanomyces/Dekkerawas dependent on the levels of SO₂and alcohol of wines. Knowledge of the contamination, the presence of ethylphenols, and their relationship with the chemical characteristics of wines can entice effective measures to prevent Brettanomyces/Dekkeraand contribute to improve the general quality of Brazilian red wines.

Key words: Brettanomyces, Dekkera, 4-ethylphenol, 4-ethylguaiacol, wine.

Introduction

Wines are subject to chemical and microbiological spoilage and yeasts of the genus Brettanomyces or its teleo–morph Dekkeracan be important causes of these problems, especially in red wines, with the production of ethylphenols and the formation of off-flavors, which are generally described as phenolic, medicinal, or animal (horse sweat, stableand leather) (Chatonnet et al., 1990). Ethylphenols, 4-ethylphenol, and 4-ethylguaiacol, are formed from the transformation of p-coumaric and ferulic acids, naturally present in wines. These transformations occur by a chain reaction of cinnamate decarboxylase generating vinyl–phe–nols, and then ethylphenols via vinylphenol reductase (He–resztyn, 1986; Lauritsen et al., 1991; Chatonnet et al., 1992). Spoilage sets up after the fermentation, usually during maturation in barrels (Chatonnet et al., 1990, 1992). The risk of microbial degradation of the wines is particularly high in wood barrels, due to the difficulty of cleaning and disinfection (Malfeito-Ferreira et al., 2004). However, the growth of Brettanomyces/Dekkeraand the formation of ethylphenols can also occur in concrete or stainless steel tanks (Rodrigues, et al., 2001), and even in bottles (Pérez-–Prieto et al., 2003).

Although all wines are susceptible to contaminations, some factors will increase this risk, for instance, when using very ripe grapes, with high contents of phenolic acids and high pH, long maceration times and difficult fermentation, which will necessarily delay the addition of sulphite (Gerbaux et al., 2000; Pérez-Prieto et al., 2003). Higher temperatures and pH (Dias et al., 2003; Romano et al., 2008), dissolved oxygen (Ciani and Ferraro, 1997), and residual sugar (Chatonnet et al., 1995), as well as the lower concentration of ethanol (Gerbaux et al., 2000) and sulphur dioxide (Chatonnet et al., 1992, 1993; Gerbaux et al., 2002; Barata et al., 2008), are other factors involved with the growth of Brettanomyces/Dekkeraand the increase of ethyl–phenols in wines.

Brettanomyces/Dekkeracan use acetic acid (Gerós et al., 2000) and ethanol (Dias et al., 2003) as the sole carbon sources, but in the presence of carbon sources commonly found in wines this metabolism is blocked (Vigentini, et al., 2008). Therefore, this yeast will grow in wines, taking advantage of even small amounts of residual sugars such as glucose, fructose, arabinose and trehalose (Chatonnet et al., 1995), arginine (Joseph and Bisson, 2004), and organic acids (Vigentini et al., 2008). Theoretically, concentrations of hexoses of 100 mg/L can support populations of Brettanomyces/Dekkeraas large as 10⁷cells/mL (Smith, 1998). Since the production of characteristic off-flavors of Brettanomyces/Dekkeracan start appearing in wines when its population is as low as 10²or 10³cells/mL, this becomes a major problem for the wine industry (Henick-Kling et al., 2000; Fugelsang and Zoecklein, 2003). Wine spoilage caused by Brettanomyces/Dekkerahas been reported worldwide (Heresztyn, 1986; Chatonnet et al., 1992; Heimoff, 1996; Ibeas et al., 1996; Fugelsang and Zoe–cklein, 2003). Brazil is becoming an important wine producer and exporter, with very typified products, and its industry is well known for its good technology, although climate conditions will frequently pose some challenges for grape quality. Little is known on the presence of Brettanomyces/Dekkerain Brazilian wines and its possible effects on wine quality. In this context, the main objective of this study was to determine the presence of these yeasts and the related ethylphenols in samples of red wines, and try to establish a relationship with other chemical characteristics of these wines, thus contributing to improve the general quality of this important product.

Materials and Methods

Chemicals

Unless otherwise stated, all chemicals were of analytical grade and purchased from Sigma-Aldrich (St. Louis, USA).

Wine samples

A total of 126 samples of 63 dry red wines were selected for this research. Wines were collected from 26 wineries located in the largest and most traditional wine region of southern Brazil, in the hills of the cities of Bento Gon–çalves and Farroupilha (RS, latitude 29°S, longitude 51°W). Samples were arranged as 54 of Cabernet Sauvignon and 63 of Merlot, while 7 were of other red varieties, and 2 were assemblage of the mentioned varieties, distributed between 2004 and 2005 vintages. Microbiological analyses were performed immediately after the opening of the bottles; the remaining wine was frozen for later chemical analysis.

Culture medium and microbiological techniques

A selective and differential medium for Brettanomyces/Dekkera(DBDM) developed by Rodrigues et al.(2001) was used in this research, with some modifications. Its basic composition is (in g/L): Yeast Nitrogen Base, 6.7; ethanol, 60; p-coumaric acid, 0.1; cyclo–hexi–mide, 0.01; bromocresol green, 0.022; agar, 20 (pH 5.4). The medium was modified by the addition of glucose (5 g/L) and chloramphenicol (0.1 g/L). This medium inhibits the growth of other yeast species due to the presence of cycloheximide. In addition, the medium allows the differentiation of the Brettanomyces/Dekkerastrains by their characteristic production of ethylphenols (off-flavors) from p-coumaric acid, the acidification, and the long incubation time required. Addition of glucose was to improve the recovery of Brettanomyces/Dekkera, and chloramphenicol, to prevent growth of bacteria.

The medium was sterilized by filtration and the agar was autoclaved separately. Varying volumes of wine were plated in agar DBDM; 0.1 mL was directly spread onto plates, while volumes of 1 and 20 mL were filtered through a 0.45 mm membrane that was placed over the medium. Colonies were counted after 3 and 14 days of incubation at 28 °C.

Determination of 4-ethylphenol and 4-ethylguaiacol

Solid phase extraction (SPE) was performed using poly–styrene-divinylbenzene cartridges Lichrolut-EN 200 mg (Merck, Darmstadt, Germany). The cartridges were conditioned with 4 mL of dichloromethane, 4 mL of methanol, and 4 mL of ethanol 12% (volume fraction). Subsequently, 50 mL of filtered wine containing 5 mg/L of an internal standard (3,4-dimethylphenol) were passed through the SPE cartridge at a flow rate of 2 mL/min. The sorbent was washed with 3 mL of ultra-pure water, dried-up by airflow for 3 min Finally, ethylphenols were eluted with 1.4 mL dichloromethane. The eluate was kept frozen until analysis. The recovery efficiencies of 4-ethylphenol and 4-ethylguaiacol using this methodology were always around 100%.

A gas chromatograph (CG-14B Shimadzu, Tokyo, Japan) equipped with flame ionization (FID) was used to determine ethylphenols. The analyses were performed by injecting mLof the eluate in split mode (ratio 1:10, 250 °C) into a DB-WAX column (60 m x 0.25 mm i.d. x 0.25 mm film thickness; Agilent J&W, Folsom, USA). The carrier gas was H₂at a flow of 1 mL/min. The temperature program was as follows: 50 °C for 1 min, first ramp to 180 °C at 10 °C/min, second ramp to 205 °C at 3 °C/min, third ramp to 215 °C at 2 °C/min, fourth ramp to 230 °C at 15 °C/min, and then kept at 230 °C for 30 min. The detector was kept at 250 °C.

General Analytical procedures

Free SO₂in wine samples was analyzed using an Oenological Analyzer (Quick, Gibertini, Milano, Italy) equipped with SO₂bubble, following titration with 0.02 N iodine solution. Total SO₂, was analyzed by steam distillation in an Oenochemical Distilling Unit (DEE, Gibertini, Milano, Italy) following titration with 0.02 N iodine solution. The ethanol content, density and total dry extract were determined using Alcolyzer Wine and density meter (DMA 4500, Anton Paar^®GmbH, Graz, Austria). Finally, residual sugar, total and volatile acidity, and pH were determined by infrared spectroscopy using a WineScan^TMFT120 (FOSS, Denmark).

Statistical analysis

Spearman correlation (r_s) analysis was used in order to correlate yeast cell numbers, concentration of ethyl–phenols and other chemical parameters of wines. Student's t-test was used to compare the average of results. The statistical analysis was performed using SPSS 16.0 software (SPSS Inc., USA).

Results and Discussion

Prevalence of Brettanomyces/Dekkerain wine samples and concentration of ethylphenols

Results for the investigation of the presence of Brettanomyces/Dekkerain wine are shown in Table 1. Thirty-four (27%) samples produced typical colonies of this yeast when they were plated onto the DBDM medium: colonies yellow to olive green, acidification of the medium, phenolic flavour and slow growth, reaching up to 2.25 x 10³CFU/mL. These values are similar to results reported by Gerbaux et al.(2000) and Rodrigues et al.(2001), in which the presence of Brettanomyceswas found in 25 and 57% of a total of 44 and 88 samples of Pinot Noir wines from the Burgundy region and Portuguese wines, respectively, containing up to 2.5 x 10³CFU/mL. This high CFU counting is of great concern for the wine industry, because it is very difficult to control Brettanomyces/Dekkerain these environments. Concerning the samples amount of ethylphenols, they were present in high percentages, above the preference thresholds for these compounds, considering the sensory impact they may cause, but were within the range reported by others authors (Table 1). Chatonnet et al.(1992) have established the limit preference thresholds of 620 mg/L for 4-ethylphenol, 140 mg/L for 4-ethylguaiacol and 426 mg/L to a 10:1 mixture of 4-ethylphenol and 4-ethylguaiacol. Average and maximal values (in mg/L) found in previous studies reached up to 1,164 and 6,047 for 4-ethylphenol, and 99 and 1,561 for 4-ethylguaiacol, respectively (Chatonnet et al., 1992; Gerbaux et al., 2000; Pollnitz et al., 2000; Rodri–gues et al., 2001; López et al., 2002; Henschke et al., 2004; Nikfardjam et al., 2009; Romano et al., 2009).

The yeast counts correlated (p < 0.01) with concentrations of 4-ethylphenol (r_s= 0.397) and 4-ethylguaiacol (r_s = 0.318) (Figure 1a). However, the prevalence of ethyl–phenols was higher than that of Brettanomyces/Dekkera, similarly observed by Rodrigues et al.(2001). One possibility for this unusual result might reside in the fact that ethylphenols were produced in an early stage in the wine, previously of procedures that would reduce the microbial load for bottling or, for the same reasons, the yeast cells could be in a non-cultivable state (Millet and Lon–vaud-–Funel, 2000). Another possibility could be the action of other yeast species such as Pichia and Candida, or bacteria such as Lactobacillus, which can produce ethylphenols (Edlin et al., 1995; Chatonnet et al., 1995, 1997; Dias et al., 2003; Couto et al., 2006; Rivas et al., 2009).

Surprisingly, the yeast counts showed variations among different bottles of the same wine, suggesting that each bottle should be individually evaluated. Thus, it would not be strictly correct to use the average of counts of different bottles of the same wine to express the presence of Brettanomyces/Dekkera. These variations among bottles were also observed and reported by other authors (Di Ste–fano, 1985; Chatonnet et al., 1993). The different environmental conditions of each fermentation tank, barrel or bottle, or different microbial loads of contaminated materials and equipment at the beginning of the bottling process may be responsible for these variations, stressing the importance of careful processing to avoid these problems.

The concentrations of 4-ethylphenol and 4-ethyl–guaiacol were statistically correlated (r_s= 0.860), and the ratio between them varied from 1.37 to 21.98, which is close to the range (1.6 to 38) found by Pollnitz et al.(2000) and Henschke et al.(2004). According to these authors, this ratio depends on the relative abundance of precursors, which is dependent on the geographic region and grape variety. Romano et al.(2008) observed the ratio of 1:1 when they used a synthetic medium containing equal concentrations of p-coumaric and ferulic acid, and the relationship with the precursors was confirmed.

Correlations with chemical parameters

In Table 2 are presented the chemical parameters of wine samples, while in Figure 1 are shown the possible correlations between these parameters and the presence of Brettanomyces/Dekkeraor concentrations of ethylphenols. Among the tested chemical parameters, only free and total SO₂, alcohol, and volatile acidity correlated with counts of Brettanomyces/Dekkeraor concentrations of ethylphenols. The average concentration of free SO₂was low (37.3% of samples), which is indicating a permissive condition for microbial growth. Most of these samples showed high levels of ethylphenols (Figure 1b) and counts of Brettanomyces/Dekkera(Figure 1c), which explains the correlation between 4-ethylphenol and free and total SO₂(r_s= -0.177 and -0.176, respectively). A free SO₂content of 30 to 40 mg/L (Gerbaux et al., 2000; Ribéreau-Gayon et al., 2003) is necessary for the total elimination of viable populations of Brettanomyces/Dekkera, and even higher doses of SO₂are required in wines with high values of pH (Su–draut and Chauvet, 1985). According to Henick-Kling et al.(2000), the wine should be maintained with at least 0.8 mg/L of molecular SO₂in order to avoid the development of Brettanomyces/Dekkera. It is known that the fraction of free SO₂in bottled wines decreases with storage time due to reactions with organic compounds and oxidation, which may explain some of the low values of free SO₂measured in this research. Notwithstanding, the total SO₂levels were also low (below 20 mg/L) in 16% of samples, which suggests that the addition of this preserving agent was carried out only once during production, leaving these wines unprotected against microbial deterioration.

The amount of alcohol weakly correlated (r_s= -0.282) with the counts of Brettanomyces/Dekkera, although most samples with high counts had up to 13% (volume fraction) of alcohol (Figure 1d), which has been suggested by some authors to be the minimal concentration showing inhibitory properties (Froudiére and Larue, 1988; Chatonnet et al., 1993; Rodrigues et al., 2001; Dias et al., 2003; Silva et al., 2004).

Regression plots showed that the highest counts of Brettanomyces/Dekkeraand concentrations of ethyl–phe–nols were found in samples in the range of 5.5 to 6.7 g tartaric acid/L total acidity.

The volatile acidity of wines was high (Table 2), if the sensorial perception threshold of 0.6 to 0.9 g/L is considered (Ough and Amerine, 1988). Twenty-three samples had volatile acidity above 1 g/L, which is detrimental to the aroma of wine. In general, the production of acetic acid by Brettanomyces/Dekkera is related to the concentration of sugar in the medium (Ciani and Ferraro, 1997; Dias et al., 2003; Abbott et al., 2005; Romano et al., 2008; Vigentini et al., 2008). It was found a weak correlation (r_s= 0.193) between volatile acidity and Brettanomyces/Dekkeracounts, but the production of acetic acid by this yeast can not be discharged, because of the high residual sugar of samples.

Brazilian legislation establishes that the maximal le–vel of residual sugar in wine to be defined as "dry wine" should not exceed 5 g/L, while a more restrict definition of dry wine, obtained by the complete fermentation of sugars, should not contain more than 1 g/L of residual sugars (Ough and Amerine, 1988). Twenty-three samples (18.25%) showed levels of sugars above 5 g/L (Table 2) suggesting that these samples were susceptible to microbial contamination. Sugar levels of 300 mg/L are considered high enough to allow the development of ethylphenols in concentrations corresponding to the perception threshold (Chatonnet et al., 1995). Silva et al.(2004) observed that residual sugar concentrations in the range of 0.1 to 12% did not show any influence on the specific growth rates of B. bruxellensisISA 1791 in mineral medium containing glucose as the sole carbon and energy source. These data suggest a lack of relationship between the residual sugar and ethylphenols concentrations, which was also observed in this work.

Presence of Brettanomyces/Dekkeraand ethylphenols correlated to the storage of wine in oak barrels

Wine samples were tested in order to investigate whether there was any effect correlated to the use of barrels during the maturation of wine on the presence of Brettanomyces/Dekkeraand ethylphenols. Table 3 presents the results for samples that were matured in wood barrels. Surprisingly, higher counts of Brettanomyces/Dekkerawere found for wines that were not matured, when compared with wine samples that were stored in barrels. However, the concentrations of ethylphenols were not statis–tically different between the two groups of samples. Wines spoilage by Brettanomyces/Dekkerahas been associated with long times of maturation in wood barrels, which presents a number of factors that contribute to the contamination (oxygen, wood porosity, small volume, etc.) (Suárez et al., 2007), but as it has been observed by some authors (Rodrigues et al., 2001; Pérez-Prieto et al., 2003; Coulo et al., 2010), the problem associated with the presence of this yeast is much more complex. The development of Brettanomyces/Dekkeraand production of ethylphenols is influenced by the practices of vinification (Chatonnet et al., 1992, 1995) and wine storage time (Pérez-Prieto et al., 2003), which may be related to the results obtained. Brazilian wineries using oak barrels on a large scale are still very few, due to the high costs of these barrels. Thus, it appears that the use of wood barrels in a small-scale production facility and shorter maturation times have favored greater care, compared with storage in stainless steel or concrete tanks, consequently reducing contaminations.

Presence of Brettanomyces/Dekkeraas a function of grape variety

In this research, the presence of Brettanomyces/Dekkerawas not found to be correlated with the variety of grape used in the wine making (Table 4), even though the Cabernet Sauvignon varieties were slightly more prone to microbial spoilage than the Merlot samples due to the characteristics of their pH and total dry extract. However, there were no statistical differences for Brettanomyces/Dekkeracounts between the two varieties, suggesting very similar winemaking practices for both varietals. The ratio of 4-ethylphenol and 4-ethylguaiacol was higher for Cabernet Sauvignon, which is linked to higher concentrations of p-coumaric acid (Pollnitz et al., 2000), with values similar to those found by others authors: 10:1 for Cabernet Sauvignon and 8:1 for Merlot (Pollnitz et al., 2000); 8:1 for Bordeaux red wines (Chatonnet et al., 1992); and around 9:1 for 180 different Chilean wines (Majce–novic, 2003).

Conclusion

The prevalence of Brettanomyces/Dekkeraand the concentrations of ethylphenols in the investigated Brazilian red wines were similar to those found for wines from other countries. The levels of contamination could be considered high, if the possible impact on sensorial aspects is taken into account. The levels of SO₂showed to be the determinant condition for microbial spoilage, since the growth of Brettanomyces/Dekkerawas dependent on the levels of SO₂and alcohol, but it seemed not to be influenced by variations in sugar, acidity and total dry extract. Despite of a well-established correlation, ethylphenols were more frequent than Brettanomyces/Dekkerain the investigated samples, and the results showed that the stage in barrels and grape varieties did not influence the levels of contamination and concentrations of ethylphenols.

Acknowledgments

The authors wish to thank Dr. Paulo Gustavo Celso of the National Agricultural Laboratory (LANAGRO, RS, Brazil) for his collaboration in this work. The authors acknowledge the financial support of CAPES (Brazil) for the first author's scholarship.

Submitted: May 24, 2011

Approved: July 2, 2012

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Publication Dates

• Publication in this collection
  26 Mar 2013
• Date of issue
  2013

History

• Received
  24 May 2011
• Accepted
  02 July 2012