Production Of Volatile Phenols Research Articles

Critical areas for <i>Brettanomyces bruxellensis</i> contamination and biofilm formation in the cellar: on the origin of wine spoilage

The cellar environment harbours a consortium of microorganisms on the material surfaces and in the air. Among these microorganisms, the spoilage yeast Brettanomyces bruxellensis can colonise surfaces due to its specific bioadhesive properties. In this study, air and surface samples were collected in several wineries during the winter period. B. bruxellensis was detected in the cellar environment either in the air or on the surfaces of various materials, including in tartaric acid precipitates. Difficult-to-clean tank equipment (taps, wall angles, valves) were identified as critical areas where B. bruxellensis was frequently detected. To confirm that surfaces contaminated by B. bruxellensis could be involved in wine contamination, yeast growth and volatile phenol production were monitored in wine in contact with stainless steel harbouring biofilms. The presence of bioadherent cells and biofilms in contact with the wine resulted in significant cell release into the wine, leading to population growth and the production of volatile phenols at concentrations above the olfactory detection threshold. This study demonstrates the possibility of wine spoilage by resident and adherent populations of B. bruxellensis and confirms the need to pay special attention to the hygiene of hard-to-reach areas such as valves.

Effect of Light and p-Coumaric Acid on the Growth and Expression of Genes Related to Oxidative Stress in Brettanomyces bruxellensis LAMAP2480.

Brettanomyces bruxellensis is considered the most significant contaminant yeast in the wine industry since it causes a deterioration in the organoleptic properties of the wine and significant economic losses. This deterioration is due to the production of volatile phenols from hydroxycinnamic acids. These compounds possess antimicrobial properties; however, B. bruxellensis can resist this effect because it metabolizes them into less toxic ones. Recent studies have reported that B. bruxellensis grows under different stress conditions, including p-coumaric acid (pCA) but effective methods for its control have not been found yet. Since that in other yeasts, such as Saccharomyces cerevisiae, it has been described that light affects its growth, and we evaluated whether the light would have a similar effect on B. bruxellensis. The results show that at light intensities of 2,500 and 4,000 lux in the absence of pCA, B. bruxellensis LAMAP2480 does not grow in the culture medium; however, when the medium contains this acid, the yeast adapts to both factors of stress managing to grow. The expression of genes related to oxidative stress in B. bruxellensis LAMAP2480, such as SOD1, GCN4, and ESBP6, showed a higher relative expression when the yeast was exposed to 2,500 lux compared to 4,000 lux, agreeing with the growth curves. This suggests that a higher expression of the genes studied would be related to stress-protective effects by pCA.

Impact of Yeast Selection on Volatile Phenol Levels of Wines Produced from Smoked-Exposed Juice

Grapes exposed to smoke can result in wines that have unacceptable high levels of volatile phenols. High volatile phenols levels have a negative impact on wine quality. This study aimed to determine the levels of volatile phenols in wines produced from smoke-exposed juice by a selection of commercial wine yeasts and to determine if yeast selection affected the perception of smokiness in wine. Commercial white and red wine yeasts were screened for the production of volatile phenols in smoke-exposed Chenin Blanc and Merlot juice. Volatile phenol levels were determined by GC-MS/MS and wines were also subjected to sensory evaluation. Volatile phenol levels in smoked wines varied and was affected by yeast strain. The highest guaiacol levels in Chenin Blanc were found in wines fermented with QA23, while Merlot wines that underwent spontaneous alcoholic fermentation contained the highest levels. The levels of volatile phenols differed significantly between the smoked and unsmoked wines, and the sensory results supported the chemical data. Volatile phenols had a negative effect on Chenin Blanc flavor profiles even when the levels were below odor detection thresholds. Yeast selection is important and can affect the volatile phenol levels and flavor profiles of wines.

Commercially Available Non-Saccharomyces Yeasts for Winemaking: Current Market, Advantages over Saccharomyces, Biocompatibility, and Safety

About 42 commercial products based on non-Saccharomyces yeasts are estimated as available on the market, being mostly pure cultures (79%), with a predominance of Torulaspora delbrueckii, Lachancea thermotolerans, and Metschnikowia pulcherrima. The others are multi-starter consortia that include non-Saccharomyces/Saccharomyces mixtures or only non-Saccharomyces species. Several commercial yeasts have shown adequate biocompatibility with S. cerevisiae in mixed fermentations, allowing an increased contribution of metabolites of oenological interest, such as glycerol, esters, higher alcohols, acids, thiols, and terpenes, among others, in addition to a lower production of acetic acid, volatile phenols, biogenic amines, or urea. Multi-starter inoculations are also reviewed here, which show adequate biocompatibility and synergy between species. In certain cases, the aromatic profile of wines based on grape varieties considered neutral is improved. In addition, several yeasts show the capacity as biocontrollers against contaminating microorganisms. The studies conducted to date demonstrate the potential of these yeasts to improve the properties of wine as an alternative and complement to the traditional S. cerevisiae.

Genetic and phenotypic diversity of Brettanomyces bruxellensis isolates from ageing wines

Brettanomyces bruxellensis is the most reported spoilage yeast in aged wines mainly due to the production of phenolic off-flavors. In the present study, 64 B. bruxellensis strains isolated from Catalonian ageing wines were genetically and physiologically evaluated. The B. bruxellensis strains had high intraspecific diversity and were distributed genetically using the polymerase chain reaction of the intron splice site (ISS-PCR) into 8 clusters, mostly depending on their origin, and into 22 clones using microsatellite analysis. Wine-like conditions resulted in poor growth of several strains but, those growing, increased their tolerance to sulfur dioxide (SO2) with incubation time. However, tolerance to SO2 was not related to the genetic clusters as defined using ISS-PCR. Furthermore, some of the strains were resistant and grew in 60 mg/L of total SO2 (2.67 mg/L molecular SO2) in wine-like conditions. Additionally, the spoilage potential of the isolated strains was evaluated using precursors of 4-ethylphenol and 4-ethylguaiacol. All the strains were able to produce these compounds above their detection threshold even if the cells were losing culturability with incubation time. Thus, both the resistance to SO2 and the production of volatile phenols varied within the strains. This complexity must be taken into account to optimize both monitoring and corrective interventions, suggesting the importance of an early detection.

Effect of malolactic fermentation and ageing on the concentration ofρ‐coumaric acid of Pinot Noir wine and the consequence for volatile phenol production byBrettanomyces

Background and Aims This study compared changes in the concentration of ρ-coumaric acid in wine because of enzymatic hydrolysis of ρ-coutaric acid by Oenocococcus oeni with that of chemical hydrolysis during ageing. Methods and Results Malolactic fermentation of a Pinot Noir wine with a cinnamoyl esterase-positive (CE+) O. oeni strain resulted in a significant increase in ρ-coumaric acid concentration. No significant change in ρ-coumaric acid concentration occurred during ageing regardless of wine pH, ethanol concentration or storage temperature. Brettanomyces bruxellensis produced a significantly higher concentration of volatile phenols in wines that underwent malolactic fermentation with the CE (+) O. oeni strain than with the CE (−) strain. Conclusions The O. oeni strain had significantly more impact on wine ρ-coumaric acid concentration than chemical hydrolysis during ageing. Significance of the Study The use of CE (+) O. oeni strains should be avoided in wines at risk of Brettanomyces spoilage because of an increase in the concentration of the volatile phenol precursor, ρ-coumaric acid.

Biodiversity among Brettanomyces bruxellensis Strains Isolated from Different Wine Regions of Chile: Key Factors Revealed about its Tolerance to Sulphite.

Brettanomyces bruxellensis is regarded as the main spoilage microorganism in the wine industry, owing to its production of off-flavours. It is difficult to eradicate owing to its high tolerance of adverse environmental conditions, such as low nutrient availability, low pH, and high levels of ethanol and SO2. In this study, the production of volatile phenols and the growth kinetics of isolates from various regions of Chile were evaluated under stressful conditions. Through randomly amplified polymorphic DNA (RAPD) analysis, 15 strains were identified. These were grown in the presence of p-coumaric acid, a natural antimicrobial and the main precursor of off-flavours, and molecular sulfur dioxide (mSO2), an antimicrobial synthetic used in the wine industry. When both compounds were used simultaneously, there were clear signs of an improvement in the fitness of most of the isolates, which showed an antagonistic interaction in which p-coumaric acid mitigates the effects of SO2. Fourteen strains were able to produce 4-vinylphenol, which showed signs of phenylacrylic acid decarboxylase activity, and most of them produced 4-ethylphenol as a result of active vinylphenol reductase. These results demonstrate for the first time the serious implications of using p-coumaric acid, not only for the production of off-flavours, but also for its protective action against the toxic effects of SO2.

Transcriptomics unravels the adaptive molecular mechanisms of Brettanomyces bruxellensis under SO2 stress in wine condition

Sulfur dioxide is generally used as an antimicrobial in wine to counteract the activity of spoilage yeasts, including Brettanomyces bruxellensis. However, this chemical does not exert the same effectiveness on different B. bruxellensis yeasts since some strains can proliferate in the final product leading to a negative sensory profile due to 4-ethylguaiacol and 4-ethylphenol. Thus, the capability of deciphering the general molecular mechanisms characterizing this yeast species’ response in presence of SO2 stress could be considered strategic for a better management of SO2 in winemaking. A RNA-Seq approach was used to investigate the gene expression of two strains of B. bruxellensis, AWRI 1499 and CBS 2499 having different genetic backgrounds, when exposed to a SO2 pulse. Results revealed that sulphites affected yeast culturability and metabolism, but not volatile phenol production suggesting that a phenotypical heterogeneity could be involved for the SO2 cell adaptation. The transcriptomics variation in response to SO2 stress confirmed the strain-related response in B. bruxellensis and the GO analysis of common differentially expressed genes showed that the detoxification process carried out by SSU1 gene can be considered as the principal specific adaptive response to counteract the SO2 presence. However, nonspecific mechanisms can be exploited by cells to assist the SO2 tolerance; namely, the metabolisms related to sugar alcohol (polyols) and oxidative stress, and structural compounds.

Brettanomyces bruxellensis phenotypic diversity, tolerance to wine stress and wine spoilage ability

Brettanomyces bruxellensis is a yeast species found in many fermented matrices. A high level of genetic diversity prevails in this species and was recently connected with tolerance to sulfur dioxide, the main preservative used in wine. We therefore examine other phenotypes that may modulate the ability of the species to spoil wine, in a selection of representative strains. The species shows a fairly high homogeneity with respect to the carbohydrates that can support growth, but more diverse behaviors regarding tolerance to low pH or ethanol. Thought no clear link can be drawn with genotype, some strains appear more tolerant than the others, mainly in the AWRI1499 like genetic group. Volatile phenol production is ubiquitous within the species, independent from yeast growth profile and not affected by the nature of the growth substrate. The specific production.n rate of volatile phenol production raises in case of increased aeration. It is little affected by pH decrease until 3.0 or by ethanol concentration increase up to 12% vol, but it decreased in case of increased constraint (pH < 3.0, Ethanol ≥14% vol) or combination of constraints. All the strain studied have thus the ability to spoil wine but some outstanding dangerous strains can even spoil the wine with high level of constrainst.

Effect of Thermosonication and Physicochemical Properties of Wine on Culturability, Viability, and Metabolic Activity of Brettanomyces bruxellensis Yeast in Red Wines

The aim of this research was to investigate the short- and long-term effects of thermosonication and different physicochemical properties of wine on culturability, viability, and metabolic activity of Brettanomyces bruxellensis yeast. Thermosonication was conducted at 43 °C during 1, 2, and 3 min, while wine variations included several pH, alcohol, and sugar levels. Cell culturability and viability were determined immediately after treatment and during 90 days of storage, while metabolic activity was determined after 90 days of storage. Results showed that, although culturability was not confirmed in dry wines immediately after 3 min of treatment, thermosonication did not result in complete inactivation of the B. bruxellensis population. Herein, the first evidence of a viable but not culturable (VBNC) state of B. bruxellensis after thermosonication exposure was observed. Moreover, thermosonication reduced the production of volatile phenols. Obtained results suggest application of thermosonication for reduction of the B. bruxellensis population only in early stages of wine contamination.

Microbiological, biochemical, physicochemical surface properties and biofilm forming ability of Brettanomyces bruxellensis

Brettanomyces bruxellensis is a serious source of concern for winemakers. The production of volatile phenols by the yeast species confers to wine unpleasant sensory characteristics which are unacceptable by the consumers and inevitably provoke economic loss for the wine industry. This ubiquitous yeast is able to adapt to all winemaking steps and to withstand various environmental conditions. Moreover, the ability of B. bruxellensis to adhere and colonize inert materials can be the cause of the yeast persistence in the cellars and thus recurrent wine spoilage. We therefore investigated the surface properties, biofilm formation capacity, and the factors which may affect the attachment of the yeast cells to surfaces with eight strains representative of the genetic diversity of the species. The eight strains of B. bruxellensis were isolated from different geographical and industrial fermentation origins. The cells were grown in synthetic YPD medium containing 1% (w/v) yeast extract (Difco Laboratories, Detroit), 2% (w/v) bacto peptone (Difco), and 1% (w/v) glucose. Surface physicochemical properties as electrophoretic mobility and adhesion to hydrocarbon of the cells were studied. The ability of the strains to form biofilm was quantified using a colorimetric microtiter 96-well polystyrene plate. Biochemical characteristics were examined by colorimetric methods as well as by chemical analysis. Our results show that the biofilm formation ability is strain-dependent and suggest a possible link between the physicochemical properties of the studied strains and their corresponding genetic group. The capacity to detect and identify the strains of the spoilage yeast based on their biofilm formation abilities may help to develop more efficient cleaning procedures and preventing methods.

Oenological characterisation of indigenous strains of S. cerevisiae isolated in a biodynamic winery in the Cortona DOC area

Genotypic and technological characterisation of the S. cerevisiae population isolated in a biodynamic winery in the Cortona DOC area was performed to gain better knowledge of the variables that influence winemaking. The oenological performance of 11 S. cerevisiae strains was evaluated with physiological tests; strain typing was performed through analysis of interdelta sequences and 26S rDNA sequencing. The analysis revealed a remarkable variability in terms of S. cerevisiae strains, despite the homogeneity of wine features, underlining the high levels of biodiversity characterising biodynamic agriculture. Some strains were found in wines of different vintages, suggesting the presence of an established microbiota in the winery. Oenological tests demonstrated that while some yeasts provided reliable oenological performance, other strains were not able to accomplish prompt and effective alcoholic fermentation, or were characterised by spoilage characteristics, such as excessive production of volatile phenols or acetic acid. Indigenous strains of S. cerevisiae could be a useful instrument for reliable winemaking without altering the native microbiota of each oenological environment. However, characterisation of their oenological suitability, and the application of practices able to drive the evolution of microbiota, must be employed to reduce the risk of wine spoilage.

Comparison of Proteomic, Metabolic, and Growth Profiles of Brettanomyces bruxellensis Isolates from Croatian Wines

Brettanomyces bruxellensis is one of the most important spoilage yeasts in red wine production. The aim of this paper was to investigate the diversity of B. bruxellensis isolates in regard to their proteomic, growth, and metabolic profiles. Ten isolates were obtained from several wineries in Croatian winegrowing regions during different phases of wine production. Proteomic analysis revealed 12 proteins that were expressed by all tested isolates and the reference strain. These proteins could be used as biomarkers in Dekkera/B. bruxellensis yeast identification. Five of these proteins were involved in carbohydrate metabolism (enolase, hxk2p, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and pyruvate decarboxylase), and four were involved in protein biosynthesis (elongation factor 1-alpha, eukaryotic translation initiation factor 5a, 60s ribosomal protein 13, and putative cytosolic ribosomal protein s24). One each was involved in cellular stress responses to glucose starvation (heat shock protein ssb1); ubiquitin conjugation pathways such as transcription, proteolysis trafficking, and kinase activation (ubiquitin); or nitrogen metabolism (peptidyl-prolyl cis-trans isomerase). Isolates identified as B. bruxellensis and taken during malolactic fermentation expressed 18 similar proteins, and isolates from aging in steel vessels/wood barrels or bottled wine expressed 23 and 24 similar proteins, respectively. Growth and metabolic profiles of these isolates were evaluated in two growth media (glucose complex and wine-mimicking media). The growth profiles of the tested isolates and conversion of hydroxycinnamic acids varied among the investigated media in that the use of glucose complex medium resulted in faster growth and consumption of hydroxycinnamic acids and in higher production of volatile phenols and esters. The results obtained suggest the possibility of applying proteomic fingerprinting for the identification and differentiation of B. bruxellensis wine isolates and reveal different spoilage capacities, such as growth and metabolic profiles, of the tested isolates.

Ethylphenol Formation by Lactobacillus plantarum: Identification of the Enzyme Involved in the Reduction of Vinylphenols.

Ethylphenols are strong odorants produced by microbial activity that are described as off flavors in several foods. Lactobacillus plantarum is a lactic acid bacterial species able to produce ethylphenols by the reduction of vinylphenols during the metabolism of hydroxycinnamic acids. However, the reductase involved has not been yet uncovered. In this study, the involvement in vinylphenol reduction of a gene encoding a putative reductase (lp_3125) was confirmed by the absence of reduction activity in the Δlp_3125 knockout mutant. The protein encoded by lp_3125, VprA, was recombinantly produced in Escherichia coli VprA was assayed against vinylphenols (4-vinylphenol, 4-vinylcatechol, and 4-vinylguaiacol), and all were reduced to their corresponding ethylphenols (4-ethylphenol, 4-ethylcatechol, and 4-ethylguaiacol). PCR and high-performance liquid chromatography (HPLC) detection methods revealed that the VprA reductase is not widely distributed among the lactic acid bacteria studied and that only the bacteria possessing the vprA gene were able to produce ethylphenol from vinylphenol. However, all the species belonging to the L. plantarum group were ethylphenol producers. The identification of the L. plantarum VprA protein involved in hydroxycinnamate degradation completes the route of degradation of these compounds in lactic acid bacteria.IMPORTANCE The presence of volatile phenols is considered a major organoleptic defect of several fermented alcoholic beverages. The biosynthesis of these compounds has been mainly associated with Brettanomyces/Dekkera yeasts. However, the potential importance of lactic acid bacteria in volatile phenol spoilage is emphasized by reports describing a faster ethylphenol production by these bacteria than by yeasts. The genetic identification of the bacterial vinylphenol reductase involved in volatile phenol production provides new insights into the role of lactic acid bacteria in the production of these off flavors. The development of a molecular method for the detection of ethylphenol-producing bacteria could be helpful to design strategies to reduce the bacterial production of vinylphenols in fermented foods.

Two Decades of “Horse Sweat” Taint and Brettanomyces Yeasts in Wine: Where do We Stand Now?

The unwanted modification of wine sensory attributes by yeasts of the species Brettanomyces bruxellensis due to the production of volatile phenols is presently the main microbiological threat to red wine quality. The effects of ethylphenols and other metabolites on wine flavor is now recognized worldwide and the object of lively debate. The focus of this review is to provide an update of the present knowledge and practice on the prevention of this problem in the wine industry. Brettanomyces bruxellensis, or its teleomorph, Dekkera bruxellensis, are rarely found in the natural environment and, although frequently isolated from fermenting substrates, their numbers are relatively low when compared with other fermenting species. Despite this rarity, they have long been studied for their unusual metabolical features (e.g., the Custers effect). Rising interest over the last decades is mostly due to volatile phenol production affecting high quality red wines worldwide. The challenges have been dealt with together by researchers and winemakers in an effective way and this has enabled a state where, presently, knowledge and prevention of the problem at the winery level is readily accessible. Today, the main issues have shifted from technological to sensory science concerning the effects of metabolites other than ethylphenols and the over estimation of the detrimental impact by ethylphenols on flavor. Hopefully, these questions will continue to be tackled together by science and industry for the benefit of wine enjoyment.

A Response Surface Methodology Approach to Investigate the Effect of Sulfur Dioxide, pH, and Ethanol on DbCD and DbVPR Gene Expression and on the Volatile Phenol Production in Dekkera/Brettanomyces bruxellensis CBS2499.

Dekkera/Brettanomyces bruxellensis, the main spoilage yeast in barrel-aged wine, metabolize hydroxycinnamic acids into off-flavors, namely ethylphenols. Recently, both the enzymes involved in this transformation, the cinnamate decarboxylase (DbCD) and the vinylphenol reductase (DbVPR), have been identified. To counteract microbial proliferation in wine, sulfur dioxide (SO2) is used commonly to stabilize the final product, but limiting its use is advised to preserve human health and boost sustainability in winemaking. In the present study, the influence of SO2 was investigated in relation with pH and ethanol factors on the expression of DbCD and DbVPR genes and volatile phenol production in D. bruxellensis CBS2499 strain under different model wines throughout a response surface methodology (RSM). In order to ensure an exact quantification of DbCD and DbVPR expression, an appropriate housekeeping gene was sought among DbPDC, DbALD, DbEF, DbACT, and DbTUB genes by GeNorm and Normfinder algorithms. The latter gene showed the highest expression stability and it was chosen as the reference housekeeping gene in qPCR assays. Even though SO2 could not be commented as main factor because of its statistical irrelevance on the response of DbCD gene, linear interactions with pH and ethanol concurred to define a significant effect (p < 0.05) on its expression. The DbCD gene was generally downregulated respect to a permissive growth condition (0 mg/L mol. SO2, pH 4.5 and 5% v/v ethanol); the combination of the factor levels that maximizes its expression (0.83-fold change) was calculated at 0.25 mg/L mol. SO2, pH 4.5 and 12.5% (v/v) ethanol. On the contrary, DbVPR expression was not influenced by main factors or by their interactions; however, its expression is maximized (1.80-fold change) at the same conditions calculated for DbCD gene. While no linear interaction between factors influenced the off-flavor synthesis, ethanol and pH produced a significant effect as individual factors. The obtained results can be useful to improve the SO2 management at the grape harvesting and during winemaking in order to minimize the D./B. bruxellensis spoilage.

Influence of Oenococcus oeni and Brettanomyces bruxellensis on Hydroxycinnamic Acids and Volatile Phenols of Aged Wine

The effect of two Oenococcus oeni strains, Viniflora® CiNe™ and Viniflora® CH11, with and without cinnamoyl esterase activity, respectively, on the contents of the hydroxycinnamic acids (HCAs) p-coumaric and ferulic acid, and their respective volatile phenols, 4-ethylphenol and 4-ethylguaiacol, was investigated over six months in Cabernet Sauvignon wines inoculated with two different Brettanomyces bruxellensis strains, CBS 73 and CBS 2499. Both CiNe™ and CH11 showed growth and malolactic fermentation in the wines. There were no clear growth interactions between B. bruxellensis and O. oeni. Furthermore, B. bruxellensis did not inhibit MLF by CiNe™ or CH11. The HCA concentrations in all wines increased until 114 days of fermentation, after which they decreased from day 114 to day 180. Wines inoculated with CiNe™ had the highest concentrations of HCAs throughout the fermentations. While CiNe™ degraded more of the tartaric ester bound forms of HCAs into free HCAs, there was no significant difference in the production of volatile phenols as compared with wines inoculated with CH11. However, there was a significant difference between wines with the two strains of B. bruxellensis in the level of volatile phenols and HCAs on day 180. Thus, the level of volatile phenols in wine depends more on strain differences of B. bruxellensis than on cinnamoyl esterase activity of O. oeni.

Growth and volatile phenol production by Brettanomyces bruxellensis in different grapevine varieties during fermentation and in finished wine

Three red grapevine varieties, Touriga Nacional, Syrah and Cabernet Sauvignon, were evaluated for their susceptibility to spoilage by two strains of Brettanomyces bruxellensis during grape juice fermentation and in finished wine. B. bruxellensis ISA 2211 survived well during both alcoholic and malolactic fermentations. The 4-ethylphenol concentration at the end of malolactic fermentation was 176 µg L−1 for T. Nacional, 190 µg L−1 for C. Sauvignon and 149 µg L−1 for Syrah. These levels were slightly increased during 3 months of incubation, even though no culturable cells of B. bruxellensis could be detected after malolactic fermentation. However, a viable but non-culturable (VBNC) population of 3–4 log cells mL−1 was observed in all grape varieties when analyzed by flow cytometry. On the other hand, commercial varietal wines, inoculated with of B. bruxellensis ISA 1791, could attain levels of 6–8 log CFU mL−1 and 4-ethylphenol reached 1750, 1512 and 2707 µg L−1 in T. Nacional, C. Sauvignon and Syrah, respectively. Overall, the production of 4-ethylphenol was mostly dependent on the existence of growing B. bruxellensis populations, regardless of the grape variety. In finished wines, 4-ethylphenol was always produced in concentrations far above its preference threshold, indicating that T. Nacional, Syrah and C. Sauvignon are equally susceptible to the “horse sweat” taint.

Production of volatile phenols by kimchi Lactobacillus plantarum isolates and factors influencing their phenolic acid decarboxylase gene expression profiles

Potential of kimchi lactic acid bacteria (LAB) isolates to produce volatile phenols and factors affecting their phenolic acid decarboxylase (padA) gene expression profiles were investigated in this study. Twelve percent (12%) of 50 tested LAB isolates were found to decarboxylate hydroxycinnamic acids. All six isolates were identified as Lactobacillus plantarum and possessed the padA gene. The highest padA expression was achieved on the third day of incubation with ferulic acid, with a relative expression of 3.30±0.32. The effects of glucose, substrate, and product concentrations, and the pH of the medium were investigated using response surface methodology for the first time in this study. The expression profiles of the padA gene were diverse in various stress environments. The concentration of p-coumaric acid was the most significant factor being positively correlated with the expression levels of the padA gene, but other factors did not show any significant effects. High concentrations of substrates could confer antibacterial activity. Therefore, decarboxylation reaction was suggested as a bacterial response to overcome the antibacterial activity. The phenolic acid decarboxylase activities of L. plantarum isolates found in this study can provide insights for their potential application in the development of food-grade flavors and additives.

Impact ofOenococcus oenion Wine Hydroxycinnamic Acids and Volatile Phenol Production byBrettanomyces bruxellensis

The ability of commercial strains of Oenococcus oeni to degrade tartaric acid ester-bound hydroxycinnamic acids (TAE-HCAs) and their impact on the production of volatile phenols by Brettanomyces bruxellensis was investigated. Of 10 commercial O. oeni strains evaluated, only one strain, O. oeni Viniflora Oenos (VFO), was able to degrade TAE-HCAs during growth in a Pinot noir wine. This degradation resulted in an increase in the corresponding free forms of the hydroxycinnamic acids in the wine. As a result, growth of B. bruxellensis UCD-2049 in Pinot noir wine where malolactic fermentation (MLF) was conducted by VFO resulted in higher concentrations of 4-ethylphenol and 4-ethylguaiacol in this wine than in wine that did not undergo MLF or underwent MLF with O. oeni strains that did not degrade TAE-HCAs. While wineries must continue to use sound winemaking practices to prevent the growth of Brettanomyces spp. in their wines, minimizing the amount of free hydroxycinnamic acids in the wine will reduce the production of volatile phenols if growth of Brettanomyces spp. does occur. The use of an O. oeni strain that cannot degrade TAE-HCAs is a simple and practical strategy to help achieve this.