Screening of enzymatic activities within different enological non-Saccharomyces yeasts

Ninety-seven non-Saccharomyces wine yeast strains belonging to ten different genera and species (Candida spp. and Criptococcus spp.; Debaryomyces hansenii, Lachancea thermotolerans, Metschnikowia pulcherrima, Pichia kluyveri, Sporidiobolus salmonicolor, Torulaspora delbrueckii, Williopsis pratensis and Zygosaccharomyces bailii) were screened for 13 enzymes related to wine aroma, color and clarity. Understanding the yeasts’ influence in these wine characteristics provides a platform for selecting strains for their development as starter cultures and for the management of alcoholic fermentation. Most of the strains showed the presence of one or more enzymes of biotechnological interest. Our screening demonstrated several intraspecific differences within the yeast species investigated, indicating that strain selection is of great importance for their enological application, and also that some non-Saccharomyces that have not been thoroughly explored, may deserve further consideration. This research represents the first stage for selecting non-Saccharomyces strains to be used as a starter along with Saccharomyces cerevisiae to enhance some particular characteristics of wines.This study has been undertaken with a Grant from the Instituto Nacional de Investigaciones Agrarias (INIA), Spain (Project RTA2013-0053-C03-03)Peer reviewe

Impact of sulphur dioxide on the viability, culturability, and volatile phenol production of Dekkera bruxellensis in wine

Viability and culturability of eight Dekkera bruxellensis strains in wine along with the accumulation of volatile phenols in response to increasing concentrations of molecular sulphur dioxide (mSO2) were investigated. mSO2 concentrations up to 1 mg/L induced the non-culturable state of a portion of the population in all the strains to a different extent for each strain, although the cells were still viable. At 1.4 mg/L mSO2, cells were non-culturable, though 0.38–29.01 % of cells retained their viability. When exposed to 2.1 mg/L mSO2, viable cells were not detected. Up to 0.24 mg/L 4-vinylguaiacol and up to 0.73 mg/L 4-ethylphenol were accumulated by non-culturable and dead Dekkera bruxellensis strains, respectively. The concentration of mSO2 needed for the transition from viable to non-culturable state of D. bruxellensis strains was higher in wine than in synthetic wine medium. The volatile phenols accumulated in wine were different from those produced in synthetic wine medium, although their accumulation kinetics were similar

Phenolic composition of monovarietal red wines regarding volatile phenols and its precursors

The aim of this study was to characterise and compare wines from different grape varieties focusing on the volatile phenols and on the respective precursor compounds, both on the free form (p-coumaric, ferulic and caffeic acids) and as tartaric esters of hydroxycinnamic acids (caftaric, coutaric and fertaric acids). Fifty-eight commercial monovarietal red wines from eight selected grape varieties were used: Cabernet Sauvignon, Syrah, Aragonez, Castelão, Touriga Franca, Touriga Nacional, Trincadeira and Vinhão (Sousão). It was found that volatile phenol precursors exist mostly as esters of tartaric acid, with caftaric acid as the most abundant cinnamate (17–111 mg/L), followed by coutaric and fertaric acids. The predominant hydroxycinnamic acid was p-coumaric acid, the highest concentrations being found in Syrah and Touriga Franca (6–7 mg/L) and the lowest in Touriga Nacional and Trincadeira (2–3 mg/L). Touriga Nacional exhibits the highest difference between bound and free forms. Malvidin-3-O-(6-p-coumaroyl)-glucoside, a potential source of p-coumaric acid, was found in most of the wines with average values varying between 1 and 5 mg/L. Twenty-two percent of the wines analysed presented levels of volatile phenols above the perception threshold. Ethylphenols were the highest in Vinhão and Trincadeira, showing an average value well above the perception threshold. The concentrations found in Cabernet Sauvignon and Syrah wines were around ten times lower than those reported in previous works. The results show relevant differences among grape varieties but the availability of the precursors in meaningful amounts may not be the only factor explaining the formation of volatile phenols in wines.info:eu-repo/semantics/publishedVersio

Analysis of grapes and the first stages of the vinification process in wine contamination with Brettanomyces bruxellensis

Brettanomyces bruxellensis is a major cause of wine spoilage due to the production of ethyl phenols, and it has become a major worldwide oenological concern in recent years. The most critical factor in volatile phenol production is the presence of microorganisms responsible for biosynthesis. In this work, carried out during three consecutive harvests, grapes and the first step in grape processing (stemmingcrushing) have been evaluated as the origin of wine contamination by these spoilage yeasts. Results showed that there was nil or minimal presence of Brettanomyces yeasts in grapes and on the stemmer, in levels that the method was not able to detect. This shows that the main contamination of wines by this microorganism occurs in later stages of the vinification process and/or during storage. The contamination of many wines with Brettanomyces, either via the fruit or from the winery environment, during the early stages of vinification and before the start of aging, was confirmed by analyzing 100 recently made red wines, in which this yeast was detected in a high percentage of wines (27 %). However, the level of Brettanomyces yeasts found in the samples was low, with values which would not be sufficient to cause organoleptic defects. Consequently, this study confirms that many wines are still tainted by Brettanomyces when the winemaking phase comes to an end. It was also found that wines with problems during fermentation had a higher level of Brettanomyces. This is why it is essential to ensure strict controls during fermentation processes and conservation to prevent wine becoming spoiled or tainted