Browsing by Author "Lima, Adriana Nunes de"
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- Survival and metabolism of hydroxycinnamic acids by Dekkera bruxellensis in monovarietal winesPublication . Lima, Adriana Nunes de; Magalhães, Rui; Campos, Francisco Manuel; Couto, José AntónioVolatile phenols in wines are responsible for unpleasant aromas, which negatively affect the quality of the wine. These compounds are produced from the metabolism of hydroxycinnamic acids, mainly by the yeasts Brettanomyces/Dekkera. Relevant data, potentially useful to support decisions on how to manage the risk of contamination of wines by Brettanomyces/Dekkera, according to the grape varieties used in the vinification, is important to the wine industry. Therefore, the aim of this work was to evaluate the survival and the metabolism of hydroxycinnamic acids by Dekkera bruxellensis in monovarietal wines. Yeast growth and survival were monitored in fifteen wines, five from each of the grape varieties Touriga Nacional, Cabernet Sauvignon and Syrah, inoculated with a strain of D. bruxellensis. Yeast culturable populations of 107 CFU mL−1 were reduced to undetectable numbers in 24 h in all wines. Plate counts of 104–106 CFU mL−1 were, however, detected after 48 h in most of Touriga Nacional and Cabernet Sauvignon wines and later in Syrah. Viability measurement by flow cytometry showed that a significant part of the populations was in a viable but non-culturable state (VBNC). The time required for the recovery of the culturable state was dependent on the wine, being longer on Syrah wines. Besides the production of ethylphenols, the metabolism of hydroxycinnamic acids by VBNC cells led to the accumulation of vinylphenols at relatively high levels, independently of the grape variety. The flow cytometry methodology showed a higher survival capacity of D. bruxellensis in Touriga Nacional wines, which corroborates with the higher amounts of volatile phenols found on this variety.
- Survival, metabolism and production of volatile phenols by Dekkera bruxellensis in monovarietal winesPublication . Lima, Adriana Nunes de; Couto, José António Gomes; Campos, Francisco Manuel Morais Sarmento deThe specific defect caused by the production of volatile phenolic compounds in wines is a major economic concern among wine producers at a global scale. Vinylphenols and, specially, ethylphenols may accumulate in wines imparting undesirable odours and flavours, which may strongly affect the wine quality. The main organisms responsible for the production of these compounds are the yeasts Brettanomyces/Dekkera. Several studies have been carried out on this subject over the last 20 years, but scientific work concerning the relationship between the grape varieties and the production of volatile phenols is extremely scarce. Thus, the overall aim of this work was to characterise the survival and metabolic behaviour of Dekkera bruxellensis in monovarietal wines and to evaluate whether certain grape varieties pose a higher risk to develop volatile phenols. The work started by searching for contaminated wines and by isolating strains of Brettanomyces/Dekkera using selective and differential culture media. The percentage of contaminated wines was 37% and all strains isolated were identified as Dekkera bruxellensis. The results support the view that, among the Brettanomyces/Dekkera yeasts, D. bruxellensis is the main species responsible for the production of volatile phenols in wines. Phenotypic variation was found among the strains studied regarding the tolerance to ethanol. The most tolerant strains were able to grow at 14% v/v ethanol and the wine isolates were, in general, more tolerant than the reference strain D. bruxellensis PYCC 4801. Strains, from the most tolerant group, were selected to perform survival and metabolic studies in real wine conditions. Prior to the metabolic studies, a chemical characterisation of monovarietal red wines from eight selected grape varieties (Cabernet Sauvignon, Syrah, Aragonez, Castelão, Touriga Franca, Touriga Nacional, Trincadeira and Vinhão) was performed, focusing on the volatile phenols and on the respective precursor compounds, both on the free and bond forms. It was found that the precursors exist mostly as esters of tartaric acid (caftaric, coutaric and fertaric acids). The predominant free hydroxycinnamic acid was p-coumaric acid, the highest concentrations being found in Syrah and Touriga Franca and the lowest in Touriga Nacional and Trincadeira. Touriga Nacional exhibited the highest difference between bound and free forms. Twenty two % of the wines analysed presented levels of volatile phenols above the perception threshold, the highest vi values being found in Vinhão and Trincadeira. The results show relevant differences among grape varieties but the availability of precursors on the free form may not be the only factor explaining the potential of wines to develop volatile phenols. The survival of D. bruxellensis in monovarietal wines (Touriga Nacional, Cabernet Sauvignon and Syrah) and the metabolism of hydroxycinnamic acids were evaluated. After the inoculation, yeast culturable populations were reduced to undetectable numbers in all wines, but viability measurement by flow cytometry showed that a significant part of the populations were in a viable-but-not-culturable state (VBNC). VBNC cells were metabolically active, causing the spoilage of the wine, and this physiological state favoured the accumulation of vinylphenols rather than ethylphenols independently of the grape variety. The survival capacity of D. bruxellensis was higher on Touriga Nacional wines than in Cabernet Sauvignon and Syrah. Wine susceptibility to Dekkera may be correlated with the phenolic composition, specifically the bound/free molar ratios of hydroxycinnamic acids. As stated above, Touriga Nacional exhibited the highest difference between bound and free forms and the level of free hydroxycinnamic acids is relatively low in comparison with other grape varieties. Therefore, the documented antimicrobial activity of free hydroxycinnamic acids may be expected to be lower in Touriga Nacional wines. Besides the production of volatile phenols, D. bruxellensis showed esterase activity leading to the increase on the amount of ethyl esters, including ethyl acetate. The fatty acids isovaleric acid and caprylic acid also increased in the inoculated wines. The concentration of monoterpenes analysed increased in the Cabernet Sauvignon wines but not in Touriga Nacional wines. The grape variety effect observed can be related with different compositions of glycosidically bound terpenes subjected to the ß-glycosidase activity of D. bruxellensis.