Saccharomyces cerevisiae and S. kudriavzevii Synthetic Wine Fermentation Performance Dissected by Predictive Modeling

Differences in metabolism among Saccharomyces species and their hybrids during wine fermentation

This study aimed to investigate how parental genomes contribute to yeast hybrid metabolism using a metabolomic approach. Previous studies have explored central carbon and nitrogen metabolism in Saccharomyces species during wine fermentation, but this study analyses the metabolomes of Saccharomyces hybrids for the first time. We evaluated the oenological performance and intra- and extracellular metabolomes, and we compared the strains according to nutrient consumption and production of the main fermentative by-products. Surprisingly, no common pattern was observed for hybrid genome influence; each strain behaved differently during wine fermentation. However, this study suggests that the genome of the S. cerevisiae species may play a more relevant role in fermentative metabolism. Variations in biomass/nitrogen ratios were also noted, potentially linked to S. kudriavzevii and S. uvarum genome contributions. These results open up possibilities for further research using different "omics" approaches to comprehend better metabolic regulation in hybrid strains with genomes from different species.

The genome sequence of the Champagne Epernay Geisenheim wine yeast reveals its hybrid nature

Lager yeasts are hybrids between Saccharomyces cerevisiae and S. eubayanus. Wine yeast biodiversity, however, has only recently been discovered to include besides pure S. cerevisiae strains also hybrids between different Saccharomyces yeasts as well as introgressions from non-Saccharomyces species. Here, we analysed the genome of the Champagne Epernay Geisenheim (CEG) wine yeast. This yeast is an allotetraploid (4n - 1) hybrid of S. cerevisiae harbouring a substantially reduced S. kudriavzevii genome contributing only 1/3 of a full genome equivalent. We identified a novel oligopeptide transporter gene, FOT4, in CEG located on chromosome XVI. FOT genes were originally derived from Torulaspora microellipsoides and FOT4 arose by non-allelic recombination between adjacent FOT1 and FOT2 genes. Fermentations of CEG in Riesling and Müller-Thurgau musts were compared with the S. cerevisiae Geisenheim wine yeast GHM, which does not carry FOT genes. At low temperature (10°C), CEG completed fermentations faster and produced increased levels of higher alcohols (e.g. isoamyl alcohol). At higher temperature (18°C), CEG produced higher amounts of the pineapple-like alkyl esters i-butyric and propionic acid ethyl esters compared to GHM. The hybrid nature of CEG thus provides advantages in grape must fermentations over S. cerevisiae wine yeasts, especially with regard to aroma production.

Wine Microbiology and Predictive Microbiology: A Short Overview on Application, and Perspectives

Predictive microbiology (PM) is an essential element in food microbiology; its aims are the determination of the responses of a given microorganism combining mathematical models with experimental data under certain environmental conditions, and the simulation a priori of the growth/inactivation of a population based on the known traits of a food matrix. Today, a great variety of models exist to describe the behaviour of several pathogenic and spoilage microorganisms in foods. In winemaking, many mathematical models have been used for monitoring yeast growth in alcoholic fermentation as well as to predict the risk of contamination of grapes and grape products by mycotoxin producing fungi over the last years, but the potentialities of PM in wine microbiology are underestimated. Thus, the goals of this review are to show some applications and perspectives in the following fields: (1) kinetics of alcoholic and malolactic fermentation; (2) models and approaches for yeasts and bacteria growth/inactivation; (3) toxin production and removal.

Monod model is insufficient to explain biomass growth in nitrogen-limited yeast fermentation

The yeast Saccharomyces cerevisiae is an essential microorganism in food biotechnology; particularly, in wine and beer making. During wine fermentation, yeasts transform sugars present in the grape juice into ethanol and carbon dioxide. The process occurs in batch conditions and is, for the most part, an anaerobic process. Previous studies linked limited-nitrogen conditions with problematic fermentations, with negative consequences for the performance of the process and the quality of the final product. It is, therefore, of the highest interest to anticipate such problems through mathematical models. Here we propose a model to explain fermentations under nitrogen-limited anaerobic conditions. We separated the biomass formation into two phases: growth and carbohydrate accumulation. Growth was modelled using the well-known Monod equation while carbohydrate accumulation was modelled by an empirical function, analogous to a proportional controller activated by the limitation of available nitrogen. We also proposed to formulate the fermentation rate as a function of the total protein content when relevant data are available. The final model was used to successfully explain experiments taken from the literature, performed under normal and nitrogen-limited conditions. Our results revealed that Monod model is insufficient to explain biomass formation kinetics in nitrogen-limited fermentations of S. cerevisiae. The goodness-of-fit of the herewith proposed model is superior to that of previously published models, offering the means to predict, and thus control fermentations. Importance: Problematic fermentations still occur in the winemaking industrial practise. Problems include sluggish rates of fermentation, which have been linked to insufficient levels of assimilable nitrogen. Data and relevant models can help anticipate poor fermentation performance. In this work, we proposed a model to predict biomass growth and fermentation rate under nitrogen-limited conditions and tested its performance with previously published experimental data. Our results show that the well-known Monod equation does not suffice to explain biomass formation.

Novel Non-Cerevisiae Saccharomyces Yeast Species Used in Beer and Alcoholic Beverage Fermentations

A great deal of research in the alcoholic beverage industry was done on non-Saccharomyces yeast strains in recent years. The increase in research interest could be attributed to the changing of consumer tastes and the search for new beer sensory experiences, as well as the rise in popularity of mixed-fermentation beers. The search for unique flavors and aromas, such as the higher alcohols and esters, polyfunctional thiols, lactones and furanones, and terpenoids that produce fruity and floral notes led to the use of non-cerevisiae Saccharomyces species in the fermentation process. Additionally, a desire to invoke new technologies and techniques for making alcoholic beverages also led to the use of new and novel yeast species. Among them, one of the most widely used non-cerevisiae strains is S. pastorianus, which was used in the production of lager beer for centuries. The goal of this review is to focus on some of the more distinct species, such as those species of Saccharomyces sensu stricto yeasts: S. kudriavzevii, S. paradoxus, S. mikatae, S. uvarum, and S. bayanus. In addition, this review discusses other Saccharomyces spp. that were used in alcoholic fermentation. Most importantly, the factors professional brewers might consider when selecting a strain of yeast for fermentation, are reviewed herein. The factors include the metabolism and fermentation potential of carbon sources, attenuation, flavor profile of fermented beverage, flocculation, optimal temperature range of fermentation, and commercial availability of each species. While there is a great deal of research regarding the use of some of these species on a laboratory scale wine fermentation, much work remains for their commercial use and efficacy for the production of beer.

Spontaneous fermentation in wine production as a controllable technology

This study focuses on the isolation of a consortium of microorganisms from spontaneously fermenting must that naturally contain lactic acid bacteria, non-saccharomyces yeasts, and saccharomyces yeasts. To collect the greatest diversity of microorganisms, the consortium was taken from the point of micro-sparkling. Based on the growth curves, isolation was performed using individual special nutrient media, and the isolates were subsequently multiplied in the nutrient medium. Individual isolates were then used for fermentation tests to monitor the percentage of fermented sugar and hydrogen sulphide production. The highest fermentation abilities were achieved in the isolates containing Saccharomyces cerevisiae and Zygosaccharomyces bailii. The smallest amount of ethanol was formed from the isolates containing Hanseniaspora uvarum, while Candida sake isolate produced the lowest amount of hydrogen sulphide and Zygosaccharomyces bailii produced the highest. The other isolates produced an average amount. Based on these results, a consortium containing the given isolates in a certain ratio was compiled.

Temperature Shapes Ecological Dynamics in Mixed Culture Fermentations Driven by Two Species of the Saccharomyces Genus

Mixed culture wine fermentations combining species within the Saccharomyces genus have the potential to produce new market tailored wines. They may also contribute to alleviating the effects of climate change in winemaking. Species, such as S. kudriavzevii, show good fermentative properties at low temperatures and produce wines with lower alcohol content, higher glycerol amounts and good aroma. However, the design of mixed culture fermentations combining S. cerevisiae and S. kudriavzevii species requires investigating their ecological interactions under cold temperature regimes. Here, we derived the first ecological model to predict individual and mixed yeast dynamics in cold fermentations. The optimal model combines the Gilpin-Ayala modification to the Lotka-Volterra competitive model with saturable competition and secondary models that account for the role of temperature. The nullcline analysis of the proposed model revealed how temperature shapes ecological dynamics in mixed co-inoculated cold fermentations. For this particular medium and species, successful mixed cultures can be achieved only at specific temperature ranges or by sequential inoculation. The proposed ecological model can be calibrated for different species and provide valuable insights into the functioning of alternative mixed wine fermentations.

Dominance of wine Saccharomyces cerevisiae strains over S. kudriavzevii in industrial fermentation competitions is related to an acceleration of nutrient uptake and utilization

Grape must is a sugar-rich habitat for a complex microbiota which is replaced by Saccharomyces cerevisiae strains during the first fermentation stages. Interest on yeast competitive interactions has recently been propelled due to the use of alternative yeasts in the wine industry to respond to new market demands. The main issue resides in the persistence of these yeasts due to the specific competitive activity of S. cerevisiae. To gather deeper knowledge of the molecular mechanisms involved, we performed a comparative transcriptomic analysis during fermentation carried out by a wine S. cerevisiae strain and a strain representative of the cryophilic S. kudriavzevii, which exhibits high genetic and physiological similarities to S. cerevisiae, but also differences of biotechnological interest. In this study, we report that transcriptomic response to the presence of a competitor is stronger in S. cerevisiae than in S. kudriavzevii. Our results demonstrate that a wine S. cerevisiae industrial strain accelerates nutrient uptake and utilization to outcompete the co-inoculated yeast, and that this process requires cell-to-cell contact to occur. Finally, we propose that this competitive phenotype evolved recently, during the adaptation of S. cerevisiae to man-manipulated fermentative environments, since a non-wine S. cerevisiae strain, isolated from a North American oak, showed a remarkable low response to competition.

Quantifying the Effects of Ethanol and Temperature on the Fitness Advantage of Predominant Saccharomyces cerevisiae Strains Occurring in Spontaneous Wine Fermentations

Different Saccharomyces cerevisiae strains are simultaneously or in succession involved in spontaneous wine fermentations. In general, few strains occur at percentages higher than 50% of the total yeast isolates (predominant strains), while a variable number of other strains are present at percentages much lower (secondary strains). Since S. cerevisiae strains participating in alcoholic fermentations may differently affect the chemical and sensory qualities of resulting wines, it is of great importance to assess whether the predominant strains possess a "dominant character." Therefore, the aim of this study was to investigate whether the predominance of some S. cerevisiae strains results from a better adaptation capability (fitness advantage) to the main stress factors of oenological interest: ethanol and temperature. Predominant and secondary S. cerevisiae strains from different wineries were used to evaluate the individual effect of increasing ethanol concentrations (0-3-5 and 7% v/v) as well as the combined effects of different ethanol concentrations (0-3-5 and 7% v/v) at different temperature (25-30 and 35°C) on yeast growth. For all the assays, the lag phase period, the maximum specific growth rate (μ_max) and the maximum cell densities were estimated. In addition, the fitness advantage between the predominant and secondary strains was calculated. The findings pointed out that all the predominant strains showed significantly higher μ_max and/or lower lag phase values at all tested conditions. Hence, S. cerevisiae strains that occur at higher percentages in spontaneous alcoholic fermentations are more competitive, possibly because of their higher capability to fit the progressively changing environmental conditions in terms of ethanol concentrations and temperature.

New Trends in the Uses of Yeasts in Oenology

The most important factor in winemaking is the quality of the final product and the new trends in oenology are dictated by wine consumers and producers. Traditionally the red wine is the most consumed and more popular; however, in the last times, the wine companies try to attract other groups of populations, especially young people and women that prefer sweet, whites or rosé wines, very fruity and with low alcohol content. Besides the new trends in consumer preferences, there are also increased concerns on the effects of alcohol consumption on health and the effects of global climate change on grape ripening and wine composition producing wines with high alcohol content. Although S. cerevisiae is the most frequent species in wines, and the subject of most studies, S. uvarum and hybrids between Saccharomyces species such as S. cerevisiae×S. kudriavzevii and S. cerevisiae×S. uvarum are also involved in wine fermentations and can be preponderant in certain wine regions. New yeast starters of non-cerevisiae strains (S. uvarum) or hybrids (S. cerevisiae×S. uvarum and S. cerevisiae×S. kudriavzevii) can contribute to solve some problems of the wineries. They exhibit good fermentative capabilities at low temperatures, producing wines with lower alcohol and higher glycerol amounts, while fulfilling the requirements of the commercial yeasts, such as a good fermentative performance and aromatic profiles that are of great interest for the wine industry. In this review, we will analyze different applications of nonconventional yeasts to solve the current winemaking demands.