Commercial Saccharomyces Cerevisiae Wine Yeast Research Articles

Influence of yeast strain, extended lees contact and nitrogen supplementation on glutathione concentration in wine

Background and Aims Glutathione (GSH) is an antioxidant that plays several important roles in wine, including the limitation of browning and of atypical ageing off-flavours and the preservation of important varietal aroma compounds. In finished wines, however, GSH concentration varies significantly. The influence of several oenological factors, including yeast strain, extended lees contact and yeast assimilable nitrogen content, on the concentration of GSH in wine and in a model wine has been investigated. Methods and Results The influence of 20 commercial Saccharomyces cerevisiae wine yeast strains on the GSH content after alcoholic fermentation was evaluated in a chemically defined grape juice (CDGJ). A significant difference was observed between strains, with some strains resulting in a GSH content sevenfold higher than that of other strains. In Sauvignon Blanc grape juice with a range of initial GSH concentration, the concentration of GSH fluctuated during fermentation. After alcoholic fermentation, however, GSH concentration was generally lower than that initially present in the juice; strains that resulted in the highest GSH concentration in the wines prepared from CDGJ did not necessarily display a similar trend in grape juice. Conclusions Yeast strains have a significant impact on the GSH concentration in finished wines, but specific outcomes are dependent on as yet unknown environmental factors. Yeast assimilable nitrogen concentration in a CDGJ did not impact on GSH concentration after fermentation, and GSH concentration generally decreases during ageing irrespective of the yeast strain or the presence of lees. Significance of the Study The data highlight the influence of certain vinification practices on the GSH concentration in wine and suggest strategies to increase the GSH concentration in commercial wines. Such strategies may help to reduce the use of sulfur dioxide by the industry.

Introducing a New Breed of Wine Yeast: Interspecific Hybridisation between a Commercial Saccharomyces cerevisiae Wine Yeast and Saccharomyces mikatae

Interspecific hybrids are commonplace in agriculture and horticulture; bread wheat and grapefruit are but two examples. The benefits derived from interspecific hybridisation include the potential of generating advantageous transgressive phenotypes. This paper describes the generation of a new breed of wine yeast by interspecific hybridisation between a commercial Saccharomyces cerevisiae wine yeast strain and Saccharomyces mikatae, a species hitherto not associated with industrial fermentation environs. While commercially available wine yeast strains provide consistent and reliable fermentations, wines produced using single inocula are thought to lack the sensory complexity and rounded palate structure obtained from spontaneous fermentations. In contrast, interspecific yeast hybrids have the potential to deliver increased complexity to wine sensory properties and alternative wine styles through the formation of novel, and wider ranging, yeast volatile fermentation metabolite profiles, whilst maintaining the robustness of the wine yeast parent. Screening of newly generated hybrids from a cross between a S. cerevisiae wine yeast and S. mikatae (closely-related but ecologically distant members of the Saccharomyces sensu stricto clade), has identified progeny with robust fermentation properties and winemaking potential. Chemical analysis showed that, relative to the S. cerevisiae wine yeast parent, hybrids produced wines with different concentrations of volatile metabolites that are known to contribute to wine flavour and aroma, including flavour compounds associated with non-Saccharomyces species. The new S. cerevisiae x S. mikatae hybrids have the potential to produce complex wines akin to products of spontaneous fermentation while giving winemakers the safeguard of an inoculated ferment.

Produção e caracterização físico-química de fermentado de umbu

O objetivo deste trabalho foi desenvolver um fermentado de umbu visando a agregar valor a esse fruto e contribuir para a melhoria de renda das famílias do semiárido nordestino. A polpa utilizada nos experimentos foi submetida a análises físico-químicas e microbiológicas. Para a produção da bebida, a polpa foi diluída em água, sendo necessário realizar uma chaptalização com sacarose até atingir 20,5°Brix. A levedura vínica comercial utilizada foi Saccharomyces cerevisiae. A fermentação foi conduzida a 18°C durante 18 dias e posteriormente a bebida foi submetida a uma estabilização com auxílio de agentes de sedimentação, gelatina e bentonita, por 14 dias a 1°C. Após a estabilização, o fermentado de umbu foi filtrado em filtro prensa. O fermentado de umbu obtido apresentou teor alcoolico de 11,20°GL. A bebida foi analisada quanto às suas características físico-químicas e todos os parâmetros estavam em conformidade com a legislação vigente.

Novel wine-mediated FLO11 flocculation phenotype of commercial Saccharomyces cerevisiae wine yeast strains with modified FLO gene expression

Depending on the genetic background of Saccharomyces strains, a wide range of phenotypic adhesion identities can be directly attributed to the FLO11-encoded glycoprotein, which includes asexual flocculation, invasive growth and pseudohyphal formation, flor formation and adhesion to biotic and abiotic surfaces. In a previous study, we reported that HSP30-mediated stationary-phase expression of the native chromosomal FLO11 ORF in two nonflocculent commercial Saccharomyces cerevisiae wine yeast strains, BM45 or VIN13 did not generate a flocculent phenotype under either standard laboratory media or synthetic MS300 must fermentation conditions. In the present study, the BM45- and VIN13-derived HSP30p-FLO11 wine yeast transformants were observed to be exclusively and strongly flocculent under authentic red wine-making conditions, thus suggesting that this specific fermentation environment specifically contributes to the development of a flocculent phenotype, which is insensitive to either glucose or mannose. Furthermore, irrespective of the strain involved this phenotype displayed both Ca(2+)-dependent and Ca(2+)-independent flocculation characteristics. A distinct advantage of this unique FLO11-based phenotype was highlighted in its ability to dramatically promote faster lees settling rates. Moreover, wines produced by BM45-F11H and VIN13-F11H transformants were significantly less turbid than those produced by their wild-type parental strains.

Population analysis of a commercial Saccharomyces cerevisiae wine yeast in a batch culture by electric particle analysis, light diffraction and flow cytometry

Data from electric particle analysis, light diffraction and flow cytometry analysis provide information on changes in cell morphology. Here, we report analyses of Saccharomyces cerevisiae populations growing in a batch culture using these techniques. The size distributions were determined by electric particle analysis and by light diffraction in order to compare their outcomes. Flow cytometry parameters forward (related to cell size) and side (related to cell granularity) scatter were also determined to complement this information. These distributions of yeast properties were analysed statistically and by a complexity index. The cell size of Saccharomyces at the lag phase was smaller than that at the beginning of the exponential phase, whereas during the stationary phase, the cell size converged with the values observed during the lag phase. These experimental techniques, when used together, allow us to distinguish among and characterize the cell size, cell granularity and the structure of the yeast population through the three growth phases. Flow cytometry patterns are better than light diffraction and electric particle analysis in showing the existence of subpopulations during the different phases, especially during the stationary phase. The use of a complexity index in this context helped to differentiate these phases and confirmed the yeast cell heterogeneity.

Differences in stationary-phase cells of a commercial Saccharomyces cerevisiae wine yeast grown in aerobic and microaerophilic batch cultures assessed by electric particle analysis, light diffraction and flow cytometry

We applied electric particle analysis, light diffraction and flow cytometry to obtain information on the morphological changes during the stationary phase of Saccharomyces cerevisiae. The reported analyses of S. cerevisiae populations were obtained under two different conditions, aerobic and microaerophilic, at 27°C. The samples analysed were taken at between 20 and 50 h from the beginning of culture. To assist in the interpretation of the observed distributions a complexity index was used. The aerobically grown culture reached significantly greater cell density. Under these conditions, the cell density experienced a much lower reduction (3%) compared with the microaerophilic conditions (30%). Under aerobic conditions, the mean cell size determined by both electric particle analysis and light diffraction was lower and remained similar throughout the experiment. Under microaerophilic conditions, the mean cell size determined by electric particle analysis decreased slightly as the culture progressed through the stationary phase. Forward and side scatter distributions revealed two cell subpopulations under both growth conditions. However, in the aerobic growing culture the two subpopulations were more separated and hence easier to distinguish. The distributions obtained with the three experimental techniques were analysed using the complexity index. This analysis suggested that a complexity index is a good descriptor of the changes that take place in a yeast population in the stationary phase, and that it aids in the discussion and understanding of the implications of these distributions obtained by these experimental techniques.

Occurrence of hydrogen sulfide in wine and in fermentation: influence of yeast strain and supplementation of yeast available nitrogen

Hydrogen sulfide (H₂S) is a powerful aroma compound largely produced by yeast during fermentation. Its occurrence in wines and other fermented beverages has been associated with off-odors described as rotten egg and/or sewage. While the formation of hydrogen sulfide (H₂S) during fermentation has been extensively studied, it is the final H₂S content of wine that is actually linked to potential off-odors. Nevertheless, factors determining final H₂S content of wine have received little attention, and it is commonly assumed that high H₂S-forming fermentations will result in high final concentrations of H₂S. However, a clear relationship has never been established. In this report, we investigated the contribution of yeast strain and nitrogen addition to H₂S formation during fermentation and its consequent occurrence the resulting wines. Five commercial Saccharomyces cerevisiae wine yeast strains were used to ferment a Chardonnay juice containing 110 mg/l of YAN (yeast assimilable nitrogen), supplemented with di-ammonium phosphate (DAP) to increase YAN concentration to moderate (260 mg/l) and high (410 mg/l) levels. In contrast to the widely reported decrease in H₂S production in response to DAP addition, a non-linear relationship was found such that moderate DAP supplementation resulted in a remarkable increase in H₂S formation by each of the five wine yeasts. H₂S content of the finished wine was affected by yeast strain, YAN, and fermentation vigor. However, we did not observe a correlation between concentration of H₂S in the finished wines and H₂S produced during fermentation, with low-forming fermentations often having relatively high final H₂S and vice versa. Management of H₂S in wine through nitrogen supplementation requires knowledge of initial YAN and yeast H₂S characteristics.

Establishing a risk-assessment process for release of genetically modified wine yeast into the environment

The use and release of genetically modified organisms (GMOs) is an issue of intense public concern and, in the case of food and beverages, products containing GMOs or products thereof carry the risk of consumer rejection. The recent commercialization of 2 GM wine yeasts in the United States and Canada has made research and development of risk assessments for GM microorganisms a priority. The purpose of this study was to take a first step in establishing a risk-assessment process for future use and potential release of GM wine yeasts into the environment. The behaviour and spread of a GM wine yeast was monitored in saturated sand columns, saturated sand flow cells, and conventional flow cells. A widely used commercial Saccharomyces cerevisiae wine yeast, VIN13, a VIN13 transgenic strain (LKA1, which carries the LKA1 alpha-amylase gene of Lipomyces kononenkoae), a soil bacterium (Dyadobacter fermentens), and a nonwine soil-borne yeast (Cryptococcus laurentii) were compared in laboratory-scale microcosm systems designed to monitor microbial mobility behaviour, survival, and attachment to surfaces. It was found that LKA1 cells survived in saturated sand columns, but showed little mobility in the porous matrix, suggesting that the cells attached with high efficiency to sand. There was no significant difference between the mobility patterns of LKA1 and VIN13. All 3 yeasts (VIN13, LKA1, and C. laurentii) were shown to form stable biofilms; the 2 S. cerevisiae strains either had no difference in biofilm density or the LKA1 biofilm was less dense than that of VIN13. When co-inoculated with C. laurentii, LKA1 had no negative influence on the breakthrough of the Cryptococcus yeast in a sand column or on its ability to form biofilms. In addition, LKA1 did not successfully integrate into a stable mixed-biofilm community, nor did it disrupt the biofilm community. Overall, it was concluded that the LKA1 transgenic yeast had the same reproductive success as VIN13 in these 3 microcosms and had no selective advantage over the untransformed parental strain.

Yeast viability during fermentation and sur lie ageing of a defined medium and subsequent growth of Oenococcus oeni

Interactions between the yeast strain used for primary oenological fermentation and the bacterium used to conduct subsequent malolactic fermentation were studied under model winemaking conditions. A commercial Saccharomyces cerevisiae wine yeast (strains, EC 1118, AWRI 835 and CY-3079) was grown in a defined medium whose composition approximated grape juice. Fermentations by all strains reached dryness, and retained a cell viability of greater than 90% upon completion of fermentation. Highest total viable cell number and percentage of viable cells were recorded for EC 1118. A sur lie ageing of the fermented medium over a 12 week period revealed a bi-phasic decay of culture viability for all strains. Thus 99% of cells had died within 2 weeks post-fermentation. Viabilities were then stable for the subsequent 4–6 week period before a second decline phase ensued and ended in either a minimal (ca 100 CFU/mL, EC 1118) or no viable cells being detected at 12 weeks of ageing. The growth response of an Oenococcus oeni inoculum to yeast culture supernatants, previously aged for up to 12 weeks in the presence or absence of yeast lees, was evaluated in a bio-assay. In this way, yeast strains could be designated as being either inhibitory, neutral or stimulatory to the growth of O. oeni (strain Lc5p). Inhibition by supernatants of strain EC 1118 was evident, but found to be reduced by ageing the supernatant (with or without lees). Conversely, longer ageing on yeast lees increased the magnitude of the stimulatory response in O. oeni (strain Lc5p) to the supernatant from the wine yeast (strain CY-3079).

Determination of sulphite reductase activity and its response to assimilable nitrogen status in a commercial Saccharomyces cerevisiae wine yeast.

The liberation of H2S is a common problem afflicting wine fermentation. Sulphite reductase activity of a commercial wine yeast was investigated to define its involvement in this process. The activity studied here differed from those characterized previously from cider and bakers' yeasts by displaying a greater sensitivity to cold, low ionic strength and possibly, proteolytic action. These differences necessitated the development of a new method of quantification. Through this method, the onset of H2S liberation was shown not to be a result of variations in the levels of sulphite reductase activity. Thus, high levels of activity which occurred during the exponential phase of growth were not necessarily accompanied by the liberation of H2S. Similarly, nitrogen-starved cultures which liberated H2S showed no corresponding increase in sulphite reductase activity from prestarvation levels. In fact, rates of H2S liberation from cultures and in enzyme assays agreed closely. A short-term independence of sulphite reductase activity from culture nitrogen status was therefore evident. The only influence of nitrogen was achieved in its absence when enzyme activity decayed with a half-life (4.25 h) which was comparable to that induced by the presence of cycloheximide (5.75 h). A proposed transcriptional control mechanism mediated by methionine derivatives was only partly effective in this strain although an in vitro inhibitory effect of methionine was implicated. These data therefore support the notion that H2S liberation in response to nitrogen starvation stems from a failure of metabolism to sequester H2S which continues to be formed, at least initially, at prestarvation rates.