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

Sci. Rep.

Brettanomyces bruxellensis is a unicellular fungus of increasing industrial and scientific interest over the past 15 years. Previous studies revealed high genotypic diversity amongst B. bruxellensis strains as well as strain-dependent phenotypic characteristics. Genomic assemblies revealed that some strains harbour triploid genomes and based upon prior genotyping it was inferred that a triploid population was widely dispersed across Australian wine regions. We performed an intraspecific diversity genotypic survey of 1488 B. bruxellensis isolates from 29 countries, 5 continents and 9 different fermentation niches. Using microsatellite analysis in combination with different statistical approaches, we demonstrate that the studied population is structured according to ploidy level, substrate of isolation and geographical origin of the strains, underlying the relative importance of each factor. We found that geographical origin has a different contribution to the population structure according to the substrate of origin, suggesting an anthropic influence on the spatial biodiversity of this microorganism of industrial interest. The observed clustering was correlated to variable stress response, as strains from different groups displayed variation in tolerance to the wine preservative sulfur dioxide (SO2). The potential contribution of the triploid state for adaptation to industrial fermentations and dissemination of the species B. bruxellensis is discussed

Starter cultures as biocontrol strategy to prevent Brettanomyces bruxellensis proliferation in wine

Brettanomyces bruxellensis is a common and significant wine spoilage microorganism. B. bruxellensis strains generally detain the molecular basis to produce compounds that are detrimental for the organoleptic quality of the wine, including some classes of volatile phenols that derive from the sequential bioconversion of specific hydroxycinnamic acids such as ferulate and pcoumarate. Although B. bruxellensis can be detected at any stage of the winemaking process, it is typically isolated at the end of the alcoholic fermentation (AF), before the staring of the spontaneous malolactic fermentation (MLF) or during barrel aging. For this reason, the endemic diffusion of B. bruxellensis leads to consistent economic losses in the wine industry. Considering the interest in reducing sulfur dioxide use during winemaking, in recent years, biological alternatives, such as the use of tailored selected yeast and bacterial strains inoculated to promote AF and MLF, are actively sought as biocontrol agents to avoid the BBretta^ character in wines. Here, we review the importance of dedicated characterization and selection of starter cultures for AF andMLF in wine, in order to reduce or prevent both growth of B. bruxellensis and its production of volatile phenols in the matrix