Yeast and its Importance to Wine Aroma - A Review

The most mysterious aspect of wine is the endless variety of flavours that stem from a complex, completely non-linear system of interactions among many hundreds of compounds. In its widest sense, wine flavour refers to the overall impression of both aroma and taste components. Aroma is usually associated with odorous, volatile compounds; the bouquet of wine refers to the more complex flavour compounds which evolve as a result of fermentation, elevage and ageing. With the exception of terpenes in the aromatic grape varieties and alkoxypyrazines in the herbaceous cultivars, perceived flavour is the result of absolute amounts and specific ratios of many of these interactive compounds, rather than being attributable to a single "impact" compound. Without underestimating the complexity of these interactive effects or negating the definitive role played by the accumulated secondary grape metabolites in the varietal character of wine, this review will focus mainly on the contribution of yeast fermentation to the sensorial quality of the final product. Yeast and fermentation conditions are claimed to be the most important factors influencing the flavours in wine. Both spontaneous and inoculated wine fermentations are affected by the diversity of yeasts associated with the vineyard and winery. During the primary alcoholic fermentation of sugar, the wine yeast, Saccharomyces cerevisiae, together with other indigenous non-Saccharomyces species, produce ethanol, carbon dioxide and a number of by-products. Of these yeast-derived metabolites, the alcohols, acetates and C4-C8 1tfatty acid ethyl esters are found in the highest concentration in wine. While the volatile metabolites contribute tothe fermentation bouquet ubiquitous to all young wines, the production levels of these by-products are variable and yeast strain specific. Therefore, this article also highlights the importance of untapping the hidden wealth of indigenous yeast species present on grapes, and the selection and genetic development of yeast starter culture strains with improved flavour profiles. In the future, some winemakers may prefer to use mixtures of indigenous yeast species and tailored S. cerevisiae strains as starter cultures to reflect the biodiversity and stylistic distinctiveness of a given region. This will help winemakers to fullfil the consumer's demand for individual wines with intact local character and to ensure the survival of wine's most enthralling aspect - its endless variety

The Influence of Different Winemaking Techniques on the Extraction of Grape Tannins and Anthocyanins

The aim of this study was to determine the effect of different maceration techniques on the extractionof grape tannins and anthocyanins. Two cultivars (Cabernet Sauvignon and Shiraz) were harvested intwo different climatic regions (Durbanville and Simondium) at two different ripeness levels for the 2008and 2009 harvest seasons. Five basic winemaking processes were applied, namely a normal alcoholicfermentation (C), enzyme treatment (E), cold soaking (CM), post-maceration (PM), and a combinationof cold and post-maceration (CM+PM). At harvest the phenolic ripeness was determined with the Gloriesmethod, while the tannin concentration was determined with the methyl cellulose (MCP) method. Thegrapes in the warmer area had higher tannin levels than grapes harvested in the cooler area in both years.In the 2009 harvest season, the enzyme treatment extracted the highest levels of tannin. CM+PM showedthe best results of tannin extraction with early ripeness (Cabernet Sauvignon), and CM with fuller ripenessin the warm area. CM showed the best results with both early and fuller ripeness levels in the cooler area.PM showed the best results with the early ripeness levels, and the E treatment with the fuller ripenesslevels, in the warm area. CM+PM showed the best results with the early ripeness level in the cooler area,and varied results with the fuller ripeness levels. In both years, grapes from the cooler area containedmore anthocyanin than those from the warmer area. At a fuller ripeness level (2009) the treatments hadno effect

Functional mechanisms underlying pleiotropic risk alleles at the 19p13.1 breast-ovarian cancer susceptibility locus

A locus at 19p13 is associated with breast cancer (BC) and ovarian cancer (OC) risk. Here we analyse 438 SNPs in this region in 46,451 BC and 15,438 OC cases, 15,252 BRCA1 mutation carriers and 73,444 controls and identify 13 candidate causal SNPs associated with serous OC (P=9.2 × 10-20), ER-negative BC (P=1.1 × 10-13), BRCA1-associated BC (P=7.7 × 10-16) and triple negative BC (P-diff=2 × 10-5). Genotype-gene expression associations are identified for candidate target genes ANKLE1 (P=2 × 10-3) and ABHD8 (P<2 × 10-3). Chromosome conformation capture identifies interactions between four candidate SNPs and ABHD8, and luciferase assays indicate six risk alleles increased transactivation of the ADHD8 promoter. Targeted deletion of a region containing risk SNP rs56069439 in a putative enhancer induces ANKLE1 downregulation; and mRNA stability assays indicate functional effects for an ANKLE1 3′-UTR SNP. Altogether, these data suggest that multiple SNPs at 19p13 regulate ABHD8 and perhaps ANKLE1 expression, and indicate common mechanisms underlying breast and ovarian cancer risk

Geographical and temporal distribution of SARS-CoV-2 clades in the WHO European Region, January to June 2020

We show the distribution of SARS-CoV-2 genetic clades over time and between countries and outline potential genomic surveillance objectives. We applied three available genomic nomenclature systems for SARS-CoV-2 to all sequence data from the WHO European Region available during the COVID-19 pandemic until 10 July 2020. We highlight the importance of real-time sequencing and data dissemination in a pandemic situation. We provide a comparison of the nomenclatures and lay a foundation for future European genomic surveillance of SARS-CoV-2.Peer reviewe

MicroRNA Related Polymorphisms and Breast Cancer Risk

Peer reviewe

MSS11, a novel yeast gene involved in the regulation of starch metabolism

Expression of the STA1-3 glucoamylase genes, responsible for starch degradation in Saccharomyces cerevisiae, is down regulated by the presence of STA10. In order to elucidate the role of STA10 in the regulation of the glucoamylase system, a multicopy genomic library was constructed and screened for genes that enhanced growth of a STA2-STA10 S. cerevisiae strain on starch media. This screen allowed us to clone and characterize a novel activator gene of STA2 (and by extrapolation, STA1 and STA3), designated MSS11. A strain transformed with multiple copies of MSS11 exhibits increased levels of STA2 mRNA and, consequently, increased glucoamylase activity. Deletion of MSS11, located on chromosome XIII, results in media-dependent absence of glucoamylase synthesis. MSS11 has not been cloned previously and the encoded protein, Mss11p, is not homologous to any other known protein. An outstanding feature of Mss11p is that the protein contains regions of 33 asparagine residues interrupted by only three serine residues, and 35 glutamine residues interrupted by a single histidine residue. Epistasis studies showed that deletion of MSS11 abolishes the activation of STA2 caused by the over-expression of MSS10, a previously identified gene. In turn, it was found that deletion of MSS10 still allows activation of STA2 by over-expression of MSS11. Mss11p therefore appears to be positioned below Mss10p in a signal transduction pathway.Articl

Effect of increased yeast alcohol acetyltransferase activity on flavor profiles of wine and distillates

The distinctive flavor of wine, brandy, and other grape-derived alcoholic beverages is affected by many compounds, including esters produced during alcoholic fermentation. The characteristic fruity odors of the fermentation bouquet are primarily due to a mixture of hexyl acetate, ethyl caproate (apple-like aroma), iso-amyl acetate (banana-like aroma), ethyl caprylate (apple-like aroma), and 2-phenylethyl acetate (fruity, flowery flavor with a honey note). The objective of this study was to investigate the feasibility of improving the aroma of wine and distillates by overexpressing one of the endogenous yeast genes that controls acetate ester production during fermentation. The synthesis of acetate esters by the wine yeast Saccharomyces cerevisiae during fermentation is ascribed to at least three acetyltransferase activities, namely, alcohol acetyltransferase (AAT), ethanol acetyltransferase, and iso-amyl AAT. To investigate the effect of increased AAT activity on the sensory quality of Chenin blanc wines and distillates from Colombar base wines, we have overexpressed the alcohol acetyltransferase gene (ATF1) of S. cerevisiae. The ATF1 gene, located on chromosome XV, was cloned from a widely used commercial wine yeast strain of S. cerevisiae, VIN13, and placed under the control of the constitutive yeast phosphoglycerate kinase gene (PGK1) promoter and terminator. Chromoblot analysis confirmed the integration of the modified copy of ATF1 into the genome of three commercial wine yeast strains (VIN7, VIN13, and WE228). Northern blot analysis indicated constitutive expression of ATF1 at high levels in these yeast transformants. The levels of ethyl acetate, iso-amyl acetate, and 2-phenylethyl acetate increased 3- to 10-fold, 3.8- to 12-fold, and 2- to 10-fold, respectively, depending on the fermentation temperature, cultivar, and yeast strain used. The concentrations of ethyl caprate, ethyl caprylate, and hexyl acetate only showed minor changes, whereas the acetic acid concentration decreased by more than half. These changes in the wine and distillate composition had a pronounced effect on the solvent or chemical aroma (associated with ethyl acetate and iso-amyl acetate) and the herbaceous and heads-associated aromas of the final distillate and the solvent or chemical and fruity or flowery characters of the Chenin blanc wines. This study establishes the concept that the overexpression of acetyltransferase genes such as ATF1 could profoundly affect the flavor profiles of wines and distillates deficient in aroma, thereby paving the way for the production of products maintaining a fruitier character for longer periods after bottling.Articl

Flocculation, Pseudohyphal Development and Invasive Growth in Commercial Wine Yeast Strains

Flocculation of Saccharomyces cerevisiae cells at the end of alcoholic fermentation is an important phenomenon in winemaking, especially in the production of bottle-fermented sparkling wine. Most wine yeast strains do not flocculate during the fermentation process and it is unknown whether they contain the necessary genes to flocculate and whether these genes are expressed adequately under wine-making conditions. These genes include the FLO1 flocculin gene which is one of the most important genes to confer the ability of yeast cells to flocculate and the MUC1 gene (subsequently also cloned as FLO11) encoding a mucin-Iike protein which was previously shown not only to play a key role in pseudohyphal development and invasive growth, but also to be involved in flocculation in S. cerevisiae.  Together with MUC1, the involvement of FL08 (encoding a transcriptional activator of FLO1) and TUPI in flocculation, pseudohyphal development and invasive growth indicates that these processes might somehow be linked. Therefore, in order to construct wine yeast strains that are able to flocculate, 25 commercial wine yeast strains were investigated for their ability to flocculate, form pseudohyphae and invade solid media.  Twenty-one of these strains were able to penetrate into agar media and different degrees of pseudohyphal and invasive growth were observed. The average length of cells and pseudohyphae and the efficiency of invasive growth varied among these strains. Two of the strains are known to flocculate in wine, while three other strains could be induced to aggregate to a limited degree in glycerol-ethanol medium. Southern blot analyses revealed the presence of homologous DNA sequences in all of the 25 strains using DNA fragments of FL08, MSS1O and MSS11 (encoding transcriptional activators of MUC1), FLO1 and MUC1 as probes. Using Northern blot analysis, FLO1 transcripts were detected in only one of the strains that showed constitutive flocculation in all the growth media tested.  MUCJ transcripts of varying sizes could be detected in most of the strains.  From these results it is clear that MUC1 does not primarily confer the phenotype of flocculation and that FLO1 (flocculation) and MUC1 (pseudohyphal differentiation, invasive growth and flocculation) are not co-regulated. We therefore suggest that MUC1, as opposed to FLO11, be retained as the most appropriate designation of this gene encoding the S. cerevisiae mucin-like protein

Flocculation, Pseudohyphal Development and Invasive Growth in Commercial Wine Yeast Strains

Flocculation of Saccharomyces cerevisiae cells at the end of alcoholic fermentation is an important phenomenon in winemaking, especially in the production of bottle-fermented sparkling wine. Most wine yeast strains do not flocculate during the fermentation process and it is unknown whether they contain the necessary genes to flocculate and whether these genes are expressed adequately under wine-making conditions. These genes include the FLO1 flocculin gene which is one of the most important genes to confer the ability of yeast cells to flocculate and the MUC1 gene (subsequently also cloned as FLO11) encoding a mucin-Iike protein which was previously shown not only to play a key role in pseudohyphal development and invasive growth, but also to be involved in flocculation in S. cerevisiae.  Together with MUC1, the involvement of FL08 (encoding a transcriptional activator of FLO1) and TUPI in flocculation, pseudohyphal development and invasive growth indicates that these processes might somehow be linked. Therefore, in order to construct wine yeast strains that are able to flocculate, 25 commercial wine yeast strains were investigated for their ability to flocculate, form pseudohyphae and invade solid media.  Twenty-one of these strains were able to penetrate into agar media and different degrees of pseudohyphal and invasive growth were observed. The average length of cells and pseudohyphae and the efficiency of invasive growth varied among these strains. Two of the strains are known to flocculate in wine, while three other strains could be induced to aggregate to a limited degree in glycerol-ethanol medium. Southern blot analyses revealed the presence of homologous DNA sequences in all of the 25 strains using DNA fragments of FL08, MSS1O and MSS11 (encoding transcriptional activators of MUC1), FLO1 and MUC1 as probes. Using Northern blot analysis, FLO1 transcripts were detected in only one of the strains that showed constitutive flocculation in all the growth media tested.  MUCJ transcripts of varying sizes could be detected in most of the strains.  From these results it is clear that MUC1 does not primarily confer the phenotype of flocculation and that FLO1 (flocculation) and MUC1 (pseudohyphal differentiation, invasive growth and flocculation) are not co-regulated. We therefore suggest that MUC1, as opposed to FLO11, be retained as the most appropriate designation of this gene encoding the S. cerevisiae mucin-like protein