Not your ordinary yeast: non-Saccharomycesyeasts in wine production uncovered

Adaptive Laboratory Evolution of Native Torulaspora delbrueckii YCPUC10 With Enhanced Ethanol Resistance and Evaluation in Co-inoculated Fermentation

Torulaspora delbrueckii is a yeast species typically present in the early stages of the fermentation process. T. delbrueckii positively modifies the aromatic properties of wines. However, its contribution to the final quality of the wine is restricted by its low tolerance to ethanol. T. delbrueckii is capable of fermenting and tolerating an ethanol concentration ranging from 7.4% (v/v) to slightly higher than 9% (v/v). For this reason, it cannot complete fermentation, when alcohol reach levels higher than 12% (v/v), limiting their use in the industry. The objective of this work was to obtain new variants of T. delbrueckii with improved resistance to ethanol through adaptive laboratory evolution. Variants capable of tolerating ethanol levels of 11.5% (v/v) were obtained. These presented improved kinetic parameters, and additionally showed an increase in resistance to SO₂ in ethanol compared to the original strain. Co-inoculated fermentations were performed with the original strain (FTd/Sc) and with the evolved strain (FTdF/Sc), in addition to a control fermentation using only Saccharomyces cerevisiae EC1118 (FSc). The results obtained show that FTdF/Sc present higher levels of 2-Ethylhexanol, compared to FTd/Sc and FSc. Furthermore, FTdF/Sc presents higher levels of total alcohols, total aldehydes, total phenolic derivatives, and total sulfur compounds with significant differences with FSc. These results provide a T. delbrueckii YCPUC10-F yeast with higher resistance to ethanol, which can be present throughout the fermentation process and be used in co-inoculated fermentations. This would positively impact the performance of T. delbrueckii by allowing it to be present not only in the early stages of fermentation but to remain until the end of fermentation.

From the vineyard to the cellar: new insights of Starmerella bacillaris (synonym Candida zemplinina) technological properties and genomic perspective

A large diversity of yeasts can be involved in alcoholic fermentation; however, Starmerella bacillaris strains have gained great attention due to their relevant and particular characteristics. S. bacillaris is commonly known as an osmotolerant, acidogenic, psychrotolerant, and fructophilic yeast. Most strains of this species are high producers of glycerol and show low ethanol production rates, being highlighted as promising alternatives to the manufacture of low-alcohol beverages. The increased production of high alcohols, such as benzyl alcohol that has antifungal and antibacterial properties, highlights S. bacillaris potential as a biocontrol agent. After harvest, antifungal yeasts become part of the must microbiota and may also improve the fermentation process. Moreover, during the fermentation, S. bacillaris releases important molecules with biotechnological properties, such as mannoproteins and glutathione. Considering the potential biotechnological properties of S. bacillaris strains, this review presents an overview of recent trends concerning the application of S. bacillaris in fermented beverages. KEY POINTS: •S. bacillaris as an alternative to the production of low-alcohol beverages. •S. bacillaris strains present biocontrol potential. •Molecules released by S. bacillaris may be of great biotechnological interest.

Grapevine Microbiota Reflect Diversity among Compartments and Complex Interactions within and among Root and Shoot Systems

Grafting connects root and shoot systems of distinct individuals, bringing microbial communities of different genotypes together in a single plant. How do root system and shoot system genotypes influence plant microbiota in grafted grapevines? To address this, we utilized clonal replicates of the grapevine ‘Chambourcin’, growing ungrafted and grafted to three different rootstocks in three irrigation treatments. Our objectives were to (1) characterize the microbiota (bacteria and fungi) of below-ground compartments (roots, adjacent soil) and above-ground compartments (leaves, berries), (2) determine how rootstock genotype, irrigation, and their interaction influences grapevine microbiota in different compartments, and (3) investigate abundance of microorganisms implicated in the late-season grapevine disease sour rot (Acetobacterales and Saccharomycetes). We found that plant compartment had the largest influence on microbial diversity. Neither rootstock genotype nor irrigation significantly influenced microbial diversity or composition. However, differential abundance of bacterial and fungal taxa varied as a function of rootstock and irrigation treatment; in particular, Acetobacterales and Saccharomycetes displayed higher relative abundance in berries of grapevines grafted to ‘1103P’ and ‘SO4’ rootstocks and varied across irrigation treatments. This study demonstrates that grapevine compartments retain distinct microbiota and identifies associations between rootstock genotypes, irrigation treatment, and the relative abundance of agriculturally relevant microorganisms in the berries.

Effects of simultaneous and sequential cofermentation of Wickerhamomyces anomalus and Saccharomyces cerevisiae on physicochemical and flavor properties of rice wine

Microorganism species and inoculation fermentation methods have great influence on physicochemical and flavor properties of rice wine. Thus, this work investigated microbial interactions and physicochemical and aroma changes of rice wine through different inoculation strategies of Wickerhamomyces anomalus (W. anomalus) and Saccharomyces cerevisiae (S. cerevisiae). The results underlined that inoculation strategies and non-Saccharomyces yeasts all affected the volatile acidity, total acidity, and alcohol content of rice wine. The sequential cofermentation consumed relatively more sugar and resulted in the higher ethanol content, causing reduced thiols and increased alcohols, esters, phenylethyls, and terpenes, which was more conducive to improve rice wine flavor than simultaneous cofermentation. Moreover, simultaneous cofermentation increased fatty aroma of rice wine, while sequential cofermentation increased mellow and cereal-like flavor. These results confirmed that sequential cofermentation of S. cerevisiae and W. anomalus was a choice for the future production of rice wine with good flavor and quality.

Secondary Aroma: Influence of Wine Microorganisms in Their Aroma Profile

Aroma profile is one of the main features for the acceptance of wine. Yeasts and bacteria are the responsible organisms to carry out both, alcoholic and malolactic fermentation. Alcoholic fermentation is in turn, responsible for transforming grape juice into wine and providing secondary aromas. Secondary aroma can be influenced by different factors; however, the influence of the microorganisms is one of the main agents affecting final wine aroma profile. Saccharomyces cerevisiae has historically been the most used yeast for winemaking process for its specific characteristics: high fermentative metabolism and kinetics, low acetic acid production, resistance to high levels of sugar, ethanol, sulfur dioxide and also, the production of pleasant aromatic compounds. Nevertheless, in the last years, the use of non-saccharomyces yeasts has been progressively growing according to their capacity to enhance aroma complexity and interact with S. cerevisiae, especially in mixed cultures. Hence, this review article is aimed at associating the main secondary aroma compounds present in wine with the microorganisms involved in the spontaneous and guided fermentations, as well as an approach to the strain variability of species, the genetic modifications that can occur and their relevance to wine aroma construction.

The Important Contribution of Non-Saccharomyces Yeasts to the Aroma Complexity of Wine: A Review

Non-Saccharomyces yeast plays an important role in the initial stages of a wild ferment, as they are found in higher abundance in the vineyard than Saccharomyces cerevisiae. As such, there has been a focus in recent years to isolate these yeast species and characterize their effect on wine fermentation and subsequent aroma. This effect on wine aroma is often species and strain dependent, as the enzymatic profile of each yeast will determine which aroma compounds are formed as secondary metabolites. Semi-fermentative yeast, such as Hanseniaspora spp., Candida spp. and Metschnikowia pulcherrima, are commonly in high abundance in fresh grape must and have diverse enzymatic profiles, however they show a weak tolerance to ethanol, limiting their impact to the initial stages of fermentation. Fully fermentative non-Saccharomyces yeast, characterized by high ethanol tolerance, are often found at low abundance in fresh grape must, similar to Saccharomyces cerevisiae. Their ability to influence the aroma profile of wine remains high, however, due to their presence into the final stages of fermentation. Some fermentative yeasts also have unique oenological properties, such as Lanchancea thermotolerans and Schizosaccharomyces pombe, highlighting the potential of these yeast as inoculants for specific wine styles.

The non-Saccharomyces yeast Pichia kluyveri for the production of aromatic volatile compounds in alcoholic fermentation

Alcoholic fermentation is influenced by yeast strain, culture media, substrate concentration and fermentation conditions, which contribute to taste and aroma. Some non-Saccharomyces yeasts are recognized as volatile compound producers that enrich aromatic profile of alcoholic beverages. In this work, 21 strains of Pichia kluyveri isolated from different fermentative processes and regions were evaluated. A principal component analysis (PCA) showed statistical differences between strains mainly associated with the variety and concentration of the compounds produced. From the PCA, two strains (PK1 and PK8) with the best volatile compound production were selected to evaluate the impact of culture media (M12 medium and Agave tequilana juice), stirring speeds (100 and 250 rpm) and temperatures (20°C, 25°C and 30°C). Increased ester production was observed at 250 rpm. Greatest effect in alcohols and ester production was found with A. tequilana, identifying PK1 as higher alcohol producer, and PK8 as better ester producer. Regarding temperature, PK1 increased ester production with decreased fermentation temperature. PK8 presented maximum levels of ethyl acetate and ethyl dodecanoate at 20°C, and finally isoamyl acetate increased its production at 30°C. Therefore, P. kluyveri strains are of great interest to produce different aromatic profiles that are affected by factors including medium, agitation and temperature.

Transformation of Microbial Negative Correlations into Positive Correlations by Saccharomyces cerevisiae Inoculation during Pomegranate Wine Fermentation

The application of starter is a common practice to accelerate and steer the pomegranate wine fermentation process. However, the use of starter needs a better understanding of the effect of the interaction between the starter and native microorganisms during alcoholic fermentation. In this study, high-throughput sequencing combined with metabolite analysis was applied to analyze the effect of commercial Saccharomyces cerevisiae inoculation on the native fungal community interaction and metabolism during pomegranate wine fermentation. Results showed that there were diverse native fungi in pomegranate juice, including Hanseniaspora uvarum, Hanseniaspora valbyensis, S. cerevisiae, Pichia terricola, and Candida diversa Based on ecological network analysis, we found that S. cerevisiae inoculation transformed the negative correlations into positive correlations among the native fungal communities and decreased the Granger causalities between native yeasts and volatile organic compounds. This might lead to decreased contents of isobutanol, isoamylol, octanoic acid, decanoic acid, ethyl laurate, ethyl acetate, ethyl hexadecanoate, phenethyl acetate, and 2-phenylethanol during fermentation. This study combined correlation and causality analysis to gain a more integrated understanding of microbial interaction and the fermentation process. It provided a new strategy to predict certain behaviors between inoculated and selected microorganisms and those coming directly from the fruit.IMPORTANCE Microbial interactions play an important role in flavor metabolism during traditional food and beverage fermentation. However, we understand little about how selected starters influence interactions among native microorganisms. In this study, we found that S. cerevisiae inoculation changed the interactions and metabolisms of native fungal communities during pomegranate wine fermentation. This study not only suggests that starter inoculation should take into account the positive features of starters but also characterizes the microbial interactions established among the starters and the native communities. It may be helpful to select appropriate starter cultures for winemakers to design different styles of wine.

Diversity and dynamics of fungi during spontaneous fermentations and association with unique aroma profiles in wine

Microbial ecology is an integral part of an agricultural ecosystem and influences the quality of agricultural commodities. Microbial activity influences grapevine health and crop production, conversion of sugar to ethanol during fermentation, thus forming wine aroma and flavour. There are regionally differentiated microbial patterns in grapevines and must but how microbial patterns contribute to wine regional distinctiveness (terroir) at small scale (<100 km) is not well defined. Here we characterise fungal communities, yeast populations, and Saccharomyces cerevisiae populations during spontaneous fermentation using metagenomics and population genetics to investigate microbial distribution and fungal contributions to the resultant wine. We found differentiation of fungi, yeasts, and S. cerevisiae between geographic origins (estate/vineyard), with influences from the grape variety. Growth and dominance of S. cerevisiae during fermentation reshaped the fungal community and showed geographic structure at the strain level. Associations between fungal microbiota diversity and wine chemicals suggest that S. cerevisiae plays a primary role in determining wine aroma profiles at a sub-regional scale. The geographic distribution at scales of less than 12 km supports that differential microbial communities, including the dominant fermentative yeast S. cerevisiae can be distinct in a local setting. These findings provide further evidence for microbial contributions to wine terroir, and perspectives for sustainable agricultural practices to maintain microbial diversity and optimise fermentation function to craft beverage quality.

Flavor Formation in Chinese Rice Wine (Huangjiu): Impacts of the Flavor-Active Microorganisms, Raw Materials, and Fermentation Technology

Huangjiu (Chinese rice wine) has been consumed for centuries in Asian countries and is known for its unique flavor and subtle taste. The flavor compounds of Huangjiu are derived from a wide range of sources, such as raw materials, microbial metabolic activities during fermentation, and chemical reactions that occur during aging. Of these sources, microorganisms have the greatest effect on the flavor quality of Huangjiu. To enrich the microbial diversity, Huangjiu is generally fermented under an open environment, as this increases the complexity of its microbial community and flavor compounds. Thus, understanding the formation of flavor compounds in Huangjiu will be beneficial for producing a superior flavored product. In this paper, a critical review of aspects that may affect the formation of Huangjiu flavor compounds is presented. The selection of appropriate raw materials and the improvement of fermentation technologies to promote the flavor quality of Huangjiu are discussed. In addition, the effects of microbial community composition, metabolic function of predominant microorganisms, and dynamics of microbial community on the flavor quality of Huangjiu are examined. This review thus provides a theoretical basis for manipulating the fermentation process by using selected microorganisms to improve the overall flavor quality of Huangjiu.

Impact of changes in wine composition produced by non-Saccharomyces on malolactic fermentation

Non-Saccharomyces yeasts have increasingly been used in vinification recently. This is particularly true of Torulaspora delbrueckii and Metschnikowia pulcherrima, which are inoculated before S. cerevisiae, to complete a sequential alcoholic fermentation. This paper aims to study the effects of these two non-Saccharomyces yeasts on malolactic fermentation (MLF) carried out by two strains of Oenococcus oeni, under cellar conditions. Oenological parameters, and volatile and phenolic compounds were analysed in wines. The wines were tasted, and the microorganisms identified. In general, non-Saccharomyces created more MLF friendly conditions, largely because of lower concentrations of SO₂ and medium chain fatty acids. The most favourable results were observed in wines inoculated with T. delbrueckii, that seemed to promote the development of O. oeni and improve MLF performance.

Effect of Saccharomyces and non-Saccharomyces native yeasts on beer aroma compounds

Recently, the increase in microbreweries and the consequent production of craft beers have reached exponential growth. The interest in non-conventional yeasts for innovation and a unique selling feature in beer fermentation is increasing. This work studied the autochthonous Saccharomyces and non-Saccharomyces yeasts, isolated from various food sources, with the ability to modify and improve the fermentative and aromatic profiles during alcoholic fermentation. The ability to ferment maltose and produce desirable aroma compounds were considered as the key characters for the screening selection. A synthetic beer wort was developed for this purpose, to simulate beer wort composition. A total of forty-seven yeast strains belonging to different genera were analysed according to their fermentation profile, volatile compounds production and sensory analysis. Three native strains of Saccharomyces cerevisiae, Zygoascus meyerae and Pichia anomala were selected to evaluate their aromatic profile in single and mixed fermentations. The strains produced 4-vinylguaiacol, β-phenylethyl alcohol, and isoamyl alcohol at levels significantly above the sensory threshold, making them interesting for wheat and blond craft beer styles. The native Hanseniaspora vineae was also included in a co-fermentation treatment, resulting in a promising yeast to produce fruity beers.

Metschnikowia pulcherrima represses aerobic respiration in Saccharomyces cerevisiae suggesting a direct response to co-cultivation

The use of non-Saccharomyces species as starter cultures together with Saccharomyces cerevisiae is becoming a common practice in the oenological industry to produce wines that respond to new market demands. In this context, microbial interactions with these non-Saccharomyces species must be considered for a rational design of yeast starter combinations. Previously, transcriptional responses of S. cerevisiae to short-term co-cultivation with Torulaspora delbrueckii, Candida sake, or Hanseniaspora uvarum was compared. An activation of sugar consumption and glycolysis, membrane and cell wall biogenesis, and nitrogen utilization was observed, suggesting a metabolic boost of S. cerevisiae in response to competing yeasts. In the present study, the transcription profile of S. cerevisiae was analyzed after 3 h of cell contact with Metschnikowia pulcherrima. Results show an over-expression of the gluco-fermentative pathway much stronger than with the other species. Moreover, a great repression of the respiration pathway has been found in response to Metschnikowia. Our hypothesis is that there is a direct interaction stress response (DISR) between S. cerevisiae and the other yeast species that, under excess sugar conditions, induces transcription of the hexose transporters, triggering glucose flow to fermentation and inhibiting respiration, leading to an increase in both, metabolic flow and population dynamics.

Formation of amino acid derivatives in white and red wines during fermentation: Effects of non-Saccharomyces yeasts and Oenococcus oeni

This study aimed to investigate the effect of commercial non-Saccharomyces yeasts and Oenococcus oeni on the formation of amino acid derivatives, some of which have neuroactive properties, during fermentation in laboratory-scale processing of white and red wines. Changes in the content of amino acid derivatives during fermentation of large-scale white and red wines were also evaluated. The highest kynurenic, picolinic, and quinolinic acid concentrations were observed in white wine fermented with Torulaspora delbrueckii, Kluyveromyces thermotolerans and Saccharomyces cerevisiae simultaneously. No changes in the content of picolinic and kynurenic acid were observed during large-scale white wine fermentation. Tryptophan ethyl ester concentration in all wines increased significantly during alcoholic fermentation. Natural and O. oeni malolactic fermentation did not alter the content of picolinic acid, a neuroprotective compound, in red wine. The decrease in the content of tyramine, phenylethylamine, and dopamine in laboratory-scale white wines was observed during alcoholic fermentation.

Shell-isolated nanoparticle-enhanced Raman spectroscopy for characterization of living yeast cells

Studying the biochemistry of yeast cells has enabled scientists to understand many essential cellular processes in human cells. Further development of biotechnological and medical progress requires revealing surface chemistry in living cells by using a non-destructive and molecular structure sensitive technique. In this study shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was applied for probing the molecular structure of Metschnikowia pulcherrima yeast cells. Important function of studied cells is the ability to eliminate iron from growth media by precipitating the insoluble pigment pulcherrimin. Comparative SERS and SHINERS analysis of the yeast cells in combination with bare Au and shell-isolated Au@SiO₂ nanoparticles were performed. It was observed that additional bands, such as adenine ring-related vibrational modes appear due to interaction with bare Au nanoparticles; the registered spectra do not coincide with the spectra where Au@SiO₂ nanoparticles were used. SHINERS spectra of M. pulcherrima were significantly enhanced comparing to the Raman spectra. Based on first-principles calculations and 830-nm excited Raman analysis of pulcherrimin, the SHINERS signatures of iron pigment in yeast cells were revealed. Being protected from direct interaction of metal with adsorbate, Au@SiO₂ nanoparticles yield reproducible and reliable vibrational signatures of yeast cell wall constituents.

How gut microbiome interactions affect nutritional traits of Drosophila melanogaster

Most research on the impact of the gut microbiome on animal nutrition is designed to identify the effects of single microbial taxa and single metabolites of microbial origin, without considering the potentially complex network of interactions among co-occurring microorganisms. Here, we investigated how different microbial associations and their fermentation products affect host nutrition, using Drosophila melanogaster colonized with three gut microorganisms (the bacteria Acetobacter fabarum and Lactobacillus brevis, and the yeast Hanseniaspora uvarum) in all seven possible combinations. Some microbial effects on host traits could be attributed to single taxa (e.g. yeast-mediated reduction of insect development time), while other effects were sex specific and driven by among-microbe interactions (e.g. male lipid content determined by interactions between the yeast and both bacteria). Parallel analysis of nutritional indices of microbe-free flies administered different microbial fermentation products (acetic acid, acetoin, ethanol and lactic acid) revealed a single consistent effect: that the lipid content of both male and female flies is reduced by acetic acid. This effect was recapitulated in male flies colonized with both yeast and A. fabarum, but not for any microbial treatment in females or males with other microbial complements. These data suggest that the effect of microbial fermentation products on host nutritional status is strongly context dependent, with respect to both the combination of associated microorganisms and host sex. Taken together, our findings demonstrate that among-microbe interactions can play a critically important role in determining the physiological outcome of host-microbiome interactions in Drosophila and, likely, in other animal hosts.

The Impact of Chitosan on the Chemical Composition of Wines Fermented with Schizosaccharomyces pombe and Saccharomyces cerevisiae

This study investigates the influence of the antimicrobial agent chitosan on a selected Schizosaccharomyces pombe strain during the alcoholic fermentation of ultra-pasteurized grape juice with a high concentration of malic acid. It also studies a selected Saccharomyces cerevisiae strain as a control. The study examines several parameters relating to wine quality, including volatile and non-volatile compounds. The principal aim of the study is to test the influence of chitosan on the final chemical composition of the wine during alcoholic fermentation, and to compare the two studied fermentative yeasts between them. The results show that chitosan influences the final concentration of acetic acid, ethanol, glycerol, acetaldehyde, pyruvic acid, α-ketoglutarate, higher alcohols, acetate esters, ethyl esters, and fatty acids, depending on the yeast species.

Drawing on the Past to Shape the Future of Synthetic Yeast Research

Some years inspire more hindsight reflection and future-gazing than others. This is even more so in 2020 with its evocation of perfect vision and the landmark ring to it. However, no futurist can reliably predict what the world will look like the next time that a year's first two digits will match the second two digits-a numerical pattern that only occurs once in a century. As we leap into a new decade, amid uncertainties triggered by unforeseen global events-such as the outbreak of a worldwide pandemic, the accompanying economic hardship, and intensifying geopolitical tensions-it is important to note the blistering pace of 21st century technological developments indicate that while hindsight might be 20/20, foresight is 50/50. The history of science shows us that imaginative ideas, research excellence, and collaborative innovation can, for example, significantly contribute to the economic, cultural, social, and environmental recovery of a post-COVID-19 world. This article reflects on a history of yeast research to indicate the potential that arises from advances in science, and how this can contribute to the ongoing recovery and development of human society. Future breakthroughs in synthetic genomics are likely to unlock new avenues of impactful discoveries and solutions to some of the world's greatest challenges.

Improved Saccharomyces cerevisiae Strain in Pure and Sequential Fermentation with Torulaspora delbrueckii for the Production of Verdicchio Wine with Reduced Sulfites

The application of yeast strains that are low producers of sulfur compounds is actually required by winemakers for the production of organic wine. This purpose could be satisfied using a native Saccharomyces cerevisiae strain improved for oenological aptitudes. Moreover, to improve the aromatic complexity of wines, sequential fermentations carried out with S. cerevisiae/non-Saccharomyces yeast is widely used. For these reasons, in the present work an improved native S. cerevisiae low producer of sulfite and sulfide compounds was evaluated in pure and in sequential fermentation with a selected Torulaspora delbrueckii. Additionally, the influence of grape juices coming from three different vintages under winery conditions was evaluated. In pure fermentation, improved native S. cerevisiae strain exhibited a behavior related to vintage, highlighting that the composition of grape juice affects the fermentation process. In particular, an increase in ethyl octanoate (vintage 2017) and phenyl ethyl acetate (vintage 2018) was detected. Moreover, isoamyl acetate was highly consistent and could be a distinctive aroma of the strain. The sequential fermentation T. delbrueckii/S. cerevisiae determined an increase in aroma compounds such as phenyl ethyl acetate and ethyl hexanoate. In this way, it was possible to produce Verdicchio wine with reduced sulfites and characterized by a peculiar aromatic taste.

Basal catalase activity and high glutathione levels influence the performance of non-Saccharomyces active dry wine yeasts

Non-Saccharomyces wine yeasts are useful tools for producing wines with complex aromas or low ethanol content. Their use in wine would benefit from their production as active dry yeast (ADY) starters to be used as co-inocula alongside S. cerevisiae. Oxidative stress during biomass propagation and dehydration is a key factor in determining ADY performance, as it affects yeast vitality and viability. Several studies have analysed the response of S. cerevisiae to oxidative stress under dehydration conditions, but not so many deal with non-conventional yeasts. In this work, we analysed eight non-Saccharomyces wine yeasts under biomass production conditions and studied oxidative stress parameters and lipid composition. The results revealed wide variability among species in their technological performance during ADY production. Also, for Metschnikowia pulcherrima and Starmerella bacillaris, better performance correlates with high catalase activity and glutathione levels. Our data suggest that non-Saccharomyces wine yeasts with an enhanced oxidative stress response are better suited to grow under ADY production conditions.

Fermentation characteristics of four non-Saccharomyces yeasts in green tea slurry

The fermentation characteristics of non-Saccharomyces yeasts (Pichia kluyveri FrootZen, Torulaspora delbrueckii Prelude, Williopsis saturnus var. mrakii NCYC2251 and Torulaspora delbrueckii Biodiva) were evaluated in green tea slurry fermentation. Each yeast showed different fermentation performances: strains Prelude and Biodiva utilized sucrose faster than the other two yeasts; strain NCYC2251 was the only species that metabolized xylose. Strain FrootZen increased the caffeine content significantly and strain Prelude showed the opposite trend, both at a statistical level, while theanine contents in four samples were relatively stable. Biodiva and FrootZen significantly improved polyphenols content and the oxygen radical absorbance capacity of fermented teas. Some endogenous volatiles such as ketones, lactones and aldehydes decreased to lower or undetected levels, but one of the key tea aroma compounds methyl salicylate increased by 34-fold and 100-fold in P. kluyveri and W. saturnus samples respectively. Therefore, green tea fermentation by appropriate non-Saccharomyces yeasts can enhance its antioxidant capacity and alter the aroma compound profile.

Discovering the indigenous microbial communities associated with the natural fermentation of sap from the cider gum Eucalyptus gunnii

Over the course of human history and in most societies, fermented beverages have had a unique economic and cultural importance. Before the arrival of the first Europeans in Australia, Aboriginal people reportedly produced several fermented drinks including mangaitch from flowering cones of Banksia and way-a-linah from Eucalyptus tree sap. In the case of more familiar fermented beverages, numerous microorganisms, including fungi, yeast and bacteria, present on the surface of fruits and grains are responsible for the conversion of the sugars in these materials into ethanol. Here we describe native microbial communities associated with the spontaneous fermentation of sap from the cider gum Eucalyptus gunnii, a Eucalyptus tree native to the remote Central Plateau of Tasmania. Amplicon-based phylotyping showed numerous microbial species in cider gum samples, with fungal species differing greatly to those associated with winemaking. Phylotyping also revealed several fungal sequences which do not match known fungal genomes suggesting novel yeast species. These findings highlight the vast microbial diversity associated with the Australian Eucalyptus gunnii and the native alcoholic beverage way-a-linah.

Proteomic characterization of extracellular vesicles produced by several wine yeast species

In winemaking, the use of alternative yeast starters is becoming increasingly popular. They contribute to the diversity and complexity of wine sensory features and are typically used in combination with Saccharomyces cerevisiae, to ensure complete fermentation. This practice has drawn the interest on interactions between different oenological yeasts, which are also relevant in spontaneous and conventional fermentations, or in the vineyard. Although several interactions have been described and some mechanisms have been suggested, the possible involvement of extracellular vesicles (EVs) has not yet been considered. This work describes the production of EVs by six wine yeast species (S. cerevisiae, Torulaspora delbrueckii, Lachancea thermotolerans, Hanseniaspora uvarum, Candida sake and Metschnikowia pulcherrima) in synthetic grape must. Proteomic analysis of EV-enriched fractions from S. cerevisiae and T. delbrueckii showed enrichment in glycolytic enzymes and cell-wall-related proteins. The most abundant protein found in S. cerevisiae, T. delbrueckii and L. thermotolerans EV-enriched fractions was the enzyme exo-1,3-β-glucanase. However, this protein was not involved in the here-observed negative impact of T. delbrueckii extracellular fractions on the growth of other yeast species. These findings suggest that EVs may play a role in fungal interactions during wine fermentation and other aspects of wine yeast biology.

Characterization of Sub-Regional Variation in Saccharomyces Populations and Grape Phenolic Composition in Pinot Noir Vineyards of a Canadian Wine Region

Wine is a product of grape juice fermentation by yeast. Terroir is a term that encompasses all environmental factors and interactions at a specific geographical site, resulting in the development of regional-specific microbial strains and grape metabolites. In this study we determine the distribution of vineyard-associated wine yeast strains and characterize the flavonoid profile of Pinot Noir grapes among 3 sub-regions in the Okanagan Valley (OV), a major wine region in British Columbia, Canada. Pinot Noir grape samples were collected from 13 vineyards among 3 sub-regions of the OV, namely Kelowna (KE), Naramata-Penticton (NP) and Oliver-Osoyoos (OO), within a week prior to the winery harvesting date in 2016 and 2017. A total of 156 spontaneous Pinot Noir fermentations were conducted and vineyard-associated Saccharomyces strains were isolated from fermentations that reached two-thirds sugar depletion. Using microsatellite genotyping, we identified 103 Saccharomyces cerevisiae strains and 9 Saccharomyces uvarum strains. We also identified Saccharomyces paradoxus in one vineyard using ITS sequencing. We developed a microsatellite database of 160 commercial S. cerevisiae strains to determine the identity of the isolated strains and we include the database herein. Commercial strains were widely distributed across the three sub-regions. Forty-two of our 103 S. cerevisiae strains were equivalent or highly similar to commercial strains whereas the remaining 61 were considered as ‘unknown’ strains. Two S. uvarum strains were previously isolated in other OV studies and none matched the S. uvarum commercial strain BMV58. S. cerevisiae population structure was driven by sub-region, although S. cerevisiae populations did not differ significantly across vintages. S. uvarum and S. paradoxus were only identified in the 2017 vintage, demonstrating dynamic wine yeast populations between vintages. We found that the flavonoid profile of Pinot Noir grapes from the same 13 vineyards was also affected by sub-regional terroir. The anthocyanin content was lower and the proportion of methoxylated anthocyanins and flavonols was higher in Pinot Noir grapes from OO, the warmer sub-region as compared to KE, the cooler sub-region. Our study demonstrates that both yeast populations and metabolites associated with the Pinot Noir variety have sub-regional variation within a viticultural area.

Isolation and Identification of Indigenous Wine Yeasts and Their Use in Alcoholic Fermentation

Research background

In our study, spontaneous alcoholic fermentations were carried out to isolate non-Saccharomyces and Saccharomyces yeasts from grape must from different vine-growing regions in Slovenia. Additionally, the diversity of native Saccharomyces cerevisiae strains was evaluated during the process.

Experimental approach

During spontaneous alcoholic fermentations the yeast population of non-Saccharomyces and Saccharomyces yeasts was sampled. We used eleven microsatellite markers to determine the genetic diversity of S. cerevisiae strains. In addition, different ratios of the indigenous strains of S. cerevisiae, Hanseniaspora uvarum and Starmerella bacillaris were tested for their possible use in alcoholic fermentation with inoculated yeasts by monitoring its course and measuring the concentration of aroma compounds in wine.

Results and conclusions

Sequencing of the internal transcribed spacer (ITS) regions of ribosomal DNA showed that of 64 isolates, 46 strains represent S. cerevisiae and 18 strains belong to non-Saccharomyces yeasts. The identified non-Saccharomyces yeast species were H. uvarum, Pichia kudriavzevii, Saturnispora diversa and S. bacillaris. The dendrogram grouped S. cerevisiae strains into 14 groups. The number of S. cervisiae strains isolated from the musts was 10 (Posavje), 11 (Podravje) and 25 (Primorska vine-growing region). On the other hand, the alcoholic fermentation with inoculated yeasts, in which the native S. cerevisiae strain predominated over H. uvarum and S. bacillaris, gave the most promising result due to the highest alcoholvolume fraction, the lowest acetic acid concentration and significantly higher concentrations of volatile thiols 3-mercaptohexyl acetate (3MHA) and 3-mercaptohexan-1-ol (3MH), 2-methylpropanol, 2-methylbutanol, 3-methylbutanol and 2-phenylethanol) in the produced wine.

Novelty and scientific contribution

We confirmed the potential use of indigenous S. cerevisiae and non-Saccharomyces yeasts in alcoholic fermentation with inoculated yeasts, which allows the positive properties of the yeast strains to be expressed and good quality wines to be produced. Thus, the results are encouraging for winemakers to create different wine styles associated with a particular terroir using indigenous yeasts.

Biodiversity of yeasts isolated during spontaneous fermentation of cool climate grape musts

Biodiversity of native yeasts, especially in winemaking, has hidden potential. In order to use the value of non-Saccharomyces strains in wine production and to minimise the possibility of its deterioration, it is necessary to thoroughly study the yeast cultures present on grape fruits and in grape must, as well as their metabolic properties. The aim of the study was to characterise the yeast microbiota found during spontaneous fermentation of grape musts obtained from grape varieties ‘Rondo’, ‘Regent’ and ‘Johanniter’. Grapes from two vineyards (Srebrna Góra and Zadora) located in southern Poland were used for the research. Succession of subsequent groups of yeasts was observed during the process. Metschnikowia pulcherrima yeasts were identified both at the beginning and the end of the process. Hanseniaspora uvarum, Wickerhamomyces onychis and Torulaspora delbrueckii strains were also identified during the fermentation. Torulaspora delbrueckii and Wickerhamomyces onychis strains were identified only in grape musts obtained from grapes of the Zadora vineyard. These strains may be characteristic of this vineyard and shape the identity of wines formed in it. Our research has provided specific knowledge on the biodiversity of yeast cultures on grapes and during their spontaneous fermentation. The research results presented indicate the possibility of using native strains for fermentation of grape musts, allowing to obtain a product with favourable chemical composition and sensory profile.

Comparison of the Glycolytic and Alcoholic Fermentation Pathways of Hanseniaspora vineae with Saccharomyces cerevisiae Wine Yeasts

Hanseniaspora species can be isolated from grapes and grape musts, but after the initiation of spontaneous fermentation, they are displaced by Saccharomyces cerevisiae. Hanseniaspora vineae is particularly valuable since this species improves the flavour of wines and has an increased capacity to ferment relative to other apiculate yeasts. Genomic, transcriptomic, and metabolomic studies in H. vineae have enhanced our understanding of its potential utility within the wine industry. Here, we compared gene sequences of 12 glycolytic and fermentation pathway enzymes from five sequenced Hanseniaspora species and S. cerevisiae with the corresponding enzymes encoded within the two sequenced H. vineae genomes. Increased levels of protein similarity were observed for enzymes of H. vineae and S. cerevisiae, relative to the remaining Hanseniaspora species. Key differences between H. vineae and H. uvarum pyruvate kinase enzymes might explain observed differences in fermentative capacity. Further, the presence of eight putative alcohol dehydrogenases, invertase activity, and sulfite tolerance are distinctive characteristics of H. vineae, compared to other Hanseniaspora species. The definition of two clear technological groups within the Hanseniaspora genus is discussed within the slow and fast evolution concept framework previously discovered in these apiculate yeasts.

The Effect of Non-Saccharomyces and Saccharomyces Non-Cerevisiae Yeasts on Ethanol and Glycerol Levels in Wine

Non-Saccharomyces and Saccharomyces non-cerevisiae studies have increased in recent years due to an interest in uninoculated fermentations, consumer preferences, wine technology, and the effect of climate change on the chemical composition of grapes, juice, and wine. The use of these yeasts to reduce alcohol levels in wines has garnered the attention of researchers and winemakers alike. This review critically analyses recent studies concerning the impact of non-Saccharomyces and Saccharomyces non-cerevisiae on two important parameters in wine: ethanol and glycerol. The influence they have in sequential, co-fermentations, and solo fermentations on ethanol and glycerol content is examined. This review highlights the need for further studies concerning inoculum rates, aeration techniques (amount and flow rate), and the length of time before Saccharomyces cerevisiae sequential inoculation occurs. Challenges include the application of such sequential inoculations in commercial wineries during harvest time.

Saccharomyces cerevisiae and Hanseniaspora uvarum mixed starter cultures: Influence of microbial/physical interactions on wine characteristics

The growing trend in the wine industry is the revaluation of the role of non-Saccharomyces yeasts, promoting the use of these yeasts in association with Saccharomyces cerevisiae. Non-Saccharomyces yeasts contribute to improve wine complexity and organoleptic composition. However, the use of mixed starters needs to better understand the effect of the interaction between these species during alcoholic fermentation. The aim of this study is to evaluate the influence of mixed starter cultures, composed by combination of different S. cerevisiae and Hanseniaspora uvarum strains, on wine characteristics and to investigate the role of cell-to-cell contact on the metabolites produced during alcoholic fermentation. In the first step, three H. uvarum and two S. cerevisiae strains, previously selected, were tested during mixed fermentations in natural red grape must in order to evaluate yeast population dynamics during inoculated fermentation and influence of mixed starter cultures on wine quality. One selected mixed starter was tested in a double-compartment fermentor in order to compare mixed inoculations of S. cerevisiae/H. uvarum with and without physical separation. Our results revealed that physical contact between S. cerevisiae and H. uvarum affected the viability of H. uvarum strain, influencing also the metabolic behaviour of the strains. Although different researches are available on the role of cell-to-cell contact-mediated interactions on cell viability of the strains included in the mixed starter, to our knowledge, very few studies have evaluated the influence of cell-to-cell contact on the chemical characteristics of wine.

The Genus Metschnikowia in Enology

Over the last decade, several non-Saccharomyces species have been used as an alternative yeast for producing wines with sensorial properties that are distinctive in comparison to those produced using only Saccharomycescerevisiae as the classical inoculum. Among the non-Saccharomyces wine yeasts, Metschnikowia is one of the most investigated genera due to its widespread occurrence and its impact in winemaking, and it has been found in grapevine phyllospheres, fruit flies, grapes, and wine fermentations as being part of the resident microbiota of wineries and wine-making equipment. The versatility that allows some Metschnikowia species to be used for winemaking relies on an ability to grow in combination with other yeast species, such as S. cerevisiae, during the first stages of wine fermentation, thereby modulating the synthesis of secondary metabolites during fermentation in order to improve the sensory profile of the wine. Metschnikowia exerts a moderate fermentation power, some interesting enzymatic activities involving aromatic and color precursors, and potential antimicrobial activity against spoilage yeasts and fungi, resulting in this yeast being considered an interesting tool for use in the improvement of wine quality. The abovementioned properties have mostly been determined from studies on Metschnikowia pulcherrima wine strains. However, M. fructicola and M. viticola have also recently been studied for winemaking purposes.

Native yeast from distinct organs of grapevines established in Queretaro, Mexico, and their potential oenological utilization

The aim of this study was to isolate, identify and determine the oenological potential of yeasts present in Vitis vinifera organs of grapevines established in Queretaro State, Mexico. The yeast distribution was influenced by the organ and the sampling season, and the yeast populations ranged from 0.8 and 5.5 Log CFU/g. A total of 93 yeasts were isolated, identified by RFLP and confirmed by sequencing of the ITS region, prevailing Aureobasidium cf. melanogenum and Basidiomycota yeast. The identified species with previously reported oenological potential were: Pichia cf. kluyveri and Clavispora cf.opuntiae. Remarkably, P. cf. kluyveri 3.1HM showed killer phenotype and was the most tolerant to sulfur dioxide, and survived 72 h after its inoculation in ‘Tempranillo’ must. C. cf. opuntiae 5.7HM showed β-glucosidase activity, the highest tolerance to 5 % ethanol and 25 °Brix (sugar levels). On the contrary, Rhodotorula isolates were not tolerant to stress conditions, and R. mucilaginosa 8HM did not grow under must conditions. Mixed fermentation using H. uvarum NB108/S. cerevisiae N05 resulted in the highest volatile acidity (0.45 g/L acetic acid), while no differences for total acidity, alcohol strength, residual sugars and total SO2 were found between the mixed fermentations treatments. This study provides an insight into the yeast diversity present in grapevines established in Queretaro, Mexico, and the oenological potential of. P. cf. kluyveri 3.1HM.

Fungal Diversity Analysis of Grape Musts from Central Valley-Chile and Characterization of Potential New Starter Cultures

Autochthonous microorganisms are an important source of the distinctive metabolites that influence the chemical profile of wine. However, little is known about the diversity of fungal communities associated with grape musts, even though they are the source of local yeast strains with potential capacities to become starters during fermentation. By using internal transcribed spacer (ITS) amplicon sequencing, we identified the taxonomic structure of the yeast community in unfermented and fermented musts of a typical Vitis vinifera L. var. Sauvignon blanc from the Central Valley of Chile throughout two consecutive seasons of production. Unsurprisingly, Saccharomyces represented the most abundant fungal genus in unfermented and fermented musts, mainly due to the contribution of S. uvarum (42.7%) and S. cerevisiae (80%). Unfermented musts were highly variable between seasons and showed higher values of fungal diversity than fermented musts. Since microbial physiological characterization is primarily achieved in culture, we isolated nine species belonging to six genera of fungi from the unfermented must samples. All isolates were characterized for their potential capacities to be used as new starters in wine. Remarkably, only Metschnikowia pulcherrima could co-exist with a commercial Saccharomyces cerevisiae strain under fermentative conditions, representing a feasible candidate strain for wine production.

New insights into the variability of lactic acid production in Lachancea thermotolerans at the phenotypic and genomic level

Non-conventional yeasts are increasingly applied in fermented beverage industry to obtain distinctive products with improved quality. Among these yeasts, Lachancea thermotolerans has multiple features of industrial relevance, especially the production of l(+)-lactic acid (LA), useful for the biological acidification of wine and beer. Since few information is available on this peculiar activity, the current study aimed to explore the physiological and genetic variability among L. thermotolerans strains. From a strain collection, mostly isolated from wine, a huge phenotypic diversity was acknowledged and allowed the selection of a high (SOL13) and a low (COLC27) LA producer. Comparative whole-genome sequencing of these two selected strains and the type strain CBS 6340^T showed a high similarity in terms of gene content and functional annotation. Notwithstanding, target gene-based analysis revealed variations between high and low producers in the key gene sequences related to LA accumulation. More in-depth investigation of the core promoters and expression analysis of the genes ldh, encoding lactate dehydrogenase, indicated the transcriptional regulation may be the principal cause behind phenotypic differences. These findings highlighted the usefulness of whole-genome sequencing coupled with expression analysis. They provided crucial genetic insights for a deeper investigation of the intraspecific variability in LA production pathway.

Oenological potential of non-Saccharomyces yeasts to mitigate effects of climate change in winemaking: impact on aroma and sensory profiles of Treixadura wines

The effects of climate change on wine include high-alcohol content, low acidity and aroma imbalance. The potential of several non-Saccharomyces wine yeasts to mitigate these effects was evaluated by sequential fermentation of Treixadura grape must. Fermentations with only Saccharomyces cerevisiae ScXG3 and a spontaneous process were used as control assays. All yeast strains were obtained from the yeast collection of Estación de Viticultura e Enoloxía de Galicia (EVEGA), Galicia, Spain. Fermentation kinetics as well as yeast dynamics and implantation ability varied depending on inoculated yeasts. In addition, the results showed significant differences in the chemical composition of wine. Starmerella bacillaris 474 reduced the alcohol content (1.1% vol) and increased the total acidity (1.2 g L-1) and glycerol of wines. Fermentation with Lachancea thermotolerans Lt93 and Torulaspora delbrueckii Td315 also decreased the alcohol content, although to a lesser extent (0.3% and 0.7% vol, respectively); however, their effect on wine acidity was less significant. The wines also differed in their concentration of volatile compounds and sensory characteristics. Thus, wines made with Metschnikowia fructicola Mf278 and S. cerevisiae ScXG3 had higher content of esters, acetates and some acids than other wines, and were most appreciated by tasters due to their fruity character and overall impression.

The microbial challenge of winemaking: yeast-bacteria compatibility

The diversity and complexity of wine environments present challenges for predicting success of fermentation. In particular, compatibility between yeast and lactic acid bacteria is affected by chemical and physical parameters that are strain and cultivar specific. This review focuses on the impact of compound production by microbes and physical interactions between microbes that ultimately influence how yeast and bacteria may work together during fermentation. This review also highlights the importance of understanding microbial interactions for yeast-bacteria compatibility in the wine context.

Dynamic of Lachancea thermotolerans Population in Monoculture and Mixed Fermentations: Impact on Wine Characteristics

Lachancea thermotolerans is a non-Saccharomyces yeast appreciated for its potential of acidification due to the production of lactic acid; however, this species also synthetizes other metabolites that modulate organoleptic wine properties. The aim of this study was to evaluate the strain L. thermotolerans Lt93 to ferment ‘Treixadura’ and ‘Mencía’ musts and its impact on yeast population dynamics and wine characteristics. Fermentations using monocultures of L. thermotolerans Lt93 and S. cerevisiae strains, sequential inoculation and spontaneous process were performed. The dynamic of yeast population and wine composition were analyzed following standard methodology. L. thermotolerans Lt93 was unable to overgrow wild yeast population in ‘Treixadura’ white must; however, with ‘Mencía’ red must, Lt93 was the predominant yeast at the beginning of fermentation and remained at high frequency until the end. Lt93 Treixadura wines had slightly higher acidity and higher content of esters and acids than ScXG3 wines. Lt93 Mencía wines presented higher acidity (10.1 g/L) and 0.8% (v/v) lower ethanol content than Sc71B wines. The content of esters and fatty acids was 3.3 and 4.0 times lower, respectively, in Lt93 than in Sc71B Mencía wines. It was possible to increase wine acidity and modulate the chemical wine profile by using Lt93.

Industrial Performance of Several Lachancea thermotolerans Strains for pH Control in White Wines from Warm Areas

In the current scenario of climatic warming, the over-ripening of grapes increases the sugar content, producing flat and alcoholic wines with low acidity, high pH and low freshness. Additionally, a high pH makes wines more chemically and microbiologically unstable, requiring a higher sulphite content for preservation. Some strains of Lachancea thermotolerans can naturally lower the pH of wine by producing lactic acid from sugars; this pH reduction can reach 0.5 units. The industrial performance of four selected strains has been compared with that of two commercial strains and with that of Saccharomyces cerevisiae. The yeasts were assessed under variable oenological conditions, measuring lactic acid production and fermentative performance at two fermentation temperatures (17 and 27 °C), and in the presence or absence of sulphites (25 and 75 mg/L). Lactic acid production depends on yeast populations, with higher concentrations being reached when the microbial population is close to or above 7-log CFU/mL. A temperature effect on acidification can also be observed, being more intense at higher fermentation temperatures for most strains. Ethanol yield ranged from 7-11% vol., depending on the fermentation conditions (temperature and SO₂) at day 12 of fermentation, compared with 12% for the S. cerevisiae control in micro-fermentations. The production of fermentative esters was higher at 27 °C compared with 17 °C, which favoured the production of higher alcohols. Volatile acidity was moderate under all fermentation conditions with values below 0.4 g/L.

Effect of Saccharomyces cerevisiae, Torulaspora delbrueckii and malolactic fermentation on fermentation kinetics and sensory property of black raspberry wines

Alcoholic fermentation (AF) and malolactic fermentation (MLF) both have significant influence on the production of black raspberry wine. In this study, three microbes associated with AF and MLF including S. cerevisiae, T. delbrueckii and O. oeni were used to investigate their combined effect on basic compositional, volatile and sensory property of black raspberry wine, and four fermentation trials including single S. cerevisiae inoculation plus spontaneous MLF (BSU) and controlled MLF with O. oeni (BSO), sequential culture of T. delbrueckii and S. cerevisiae plus spontaneous MLF (BTSU) and controlled MLF (BTSO) were tested and compared. Fermentation results showed MLF in BSU, BSO and BTSO were successful, with respective period of 40, 25 and 23 days, whereas a stuck MLF occurred in BTSU. Volatile compounds were determined by HS-GC-IMS method, with a total of 45 aromas identified. BTSO was distinguished by a significant higher signal intensity of many fruity esters and a lower production of several alcohols and terpenes, which was in agreement with its perception result of strong 'fruity' and slight note of 'solvent' and 'herbaceous' during quantitative descriptive analysis. On the contrary, BSU was found to reinforce the synthesis of most detected volatiles, resulting in the enhancement of both beneficial and off-flavour compounds, therefore scoring lower in the 'global aroma' descriptor. Principal component analysis showed BSU and BSO were similar in the volatile composition, whereas BTSO was quite different. Overall, BTSO had greater potential to be used in the production of black raspberry wine.

Investigations of the mechanisms of interactions between four non-conventional species with Saccharomyces cerevisiae in oenological conditions

Fermentation by microorganisms is a key step in the production of traditional food products such as bread, cheese, beer and wine. In these fermentative ecosystems, microorganisms interact in various ways, namely competition, predation, commensalism and mutualism. Traditional wine fermentation is a complex microbial process performed by Saccharomyces and non-Saccharomyces (NS) yeast species. To better understand the different interactions occurring within wine fermentation, isolated yeast cultures were compared with mixed co-cultures of one reference strain of S. cerevisiae with one strain of four NS yeast species (Metschnikowia pulcherrima, M. fructicola, Hanseniaspora opuntiae and H. uvarum). In each case, we studied population dynamics, resource consumed and metabolites produced from central carbon metabolism. This phenotyping of competition kinetics allowed us to confirm the main mechanisms of interaction between strains of four NS species. S. cerevisiae competed with H. uvarum and H. opuntiae for resources although both Hanseniaspora species were characterized by a strong mortality either in mono or mixed fermentations. M. pulcherrima and M. fructicola displayed a negative interaction with the S. cerevisiae strain tested, with a decrease in viability in co-culture. Overall, this work highlights the importance of measuring specific cell populations in mixed cultures and their metabolite kinetics to understand yeast-yeast interactions. These results are a first step towards ecological engineering and the rational design of optimal multi-species starter consortia using modeling tools. In particular the originality of this paper is for the first times to highlight the joint-effect of different species population dynamics on glycerol production and also to discuss on the putative role of lipid uptake on the limitation of some non-conventional species growth although interaction processes.

PTR-ToF-MS for the Online Monitoring of Alcoholic Fermentation in Wine: Assessment of VOCs Variability Associated with Different Combinations of Saccharomyces/Non-Saccharomyces as a Case-Study

The management of the alcoholic fermentation (AF) in wine is crucial to shaping product quality. Numerous variables (e.g., grape varieties, yeast species/strains, technological parameters) can affect the performances of this fermentative bioprocess. The fact that these variables are often interdependent, with a high degree of interaction, leads to a huge ‘oenological space’ associated with AF that scientists and professionals have explored to obtain the desired quality standards in wine and to promote innovation. This challenge explains the high interest in approaches tested to monitor this bioprocess including those using volatile organic compounds (VOCs) as target molecules. Among direct injection mass spectrometry approaches, no study has proposed an untargeted online investigation of the diversity of volatiles associated with the wine headspace. This communication proposed the first application of proton-transfer reaction-mass spectrometry coupled to a time-of-flight mass analyzer (PTR-ToF-MS) to follow the progress of AF and evaluate the impact of the different variables of wine quality. As a case study, the assessment of VOC variability associated with different combinations of Saccharomyces/non-Saccharomyces was selected. The different combinations of microbial resources in wine are among the main factors susceptible to influencing the content of VOCs associated with the wine headspaces. In particular, this investigation explored the effect of multiple combinations of two Saccharomyces strains and two non-Saccharomyces strains (belonging to the species Metschnikowia pulcherrima and Torulaspora delbrueckii) on the content of VOCs in wine, inoculated both in commercial grape juice and fresh grape must. The results demonstrated the possible exploitation of non-invasive PTR-ToF-MS monitoring to explore, using VOCs as biomarkers, (i) the huge number of variables influencing AF in wine, and (ii) applications of single/mixed starter cultures in wine. Reported preliminary findings underlined the presence of different behaviors on grape juice and on must, respectively, and confirmed differences among the single yeast strains ‘volatomes’. It was one of the first studies to include the simultaneous inoculation on two non-Saccharomyces species together with a S. cerevisiae strain in terms of VOC contribution. Among the other outcomes, evidence suggests that the addition of M. pulcherrima to the coupled S. cerevisiae/T. delbrueckii can modify the global release of volatiles as a function of the characteristics of the fermented matrix.

Wine Yeast Terroir: Separating the Wheat from the Chaff-for an Open Debate

Wine terroir is characterized by a specific taste and style influenced by the cultivar of the fermented grapes, geographical factors such as the vineyard, mesoclimate, topoclimate, and microclimate, soil geology and pedology, and the agronomic approach used. These characteristics together define the concept of "terroir". Thus, regional distinctive flavors in wine have been the subject of many studies aimed at better understanding the link between the wine and the vineyard. Indeed, the identification of key environmental elements involved in the regional variation of grape and wine quality characteristics is a critical feature for improving wine production in terms of consumer preference and economic appreciation. Many studies have demonstrated the role of abiotic factors in grape composition and consequently in wine style. Biotic factors are also involved such as grape microbial communities. However, the occurrence and effects of region-specific microbiota in defining wine characteristics are more controversial issues. Indeed, several studies using high throughput sequencing technologies have made it possible to describe microbial communities and revealed a link between grape must and soil microbial communities, and the geography of the territory. Based on these observations, the concept of "microbial terroir" emerged. However, this concept has been subject to contradictory studies. The aim of this opinion article is to take a step back and examine in perspective the concept of microbial terroir, by comparing numerous data from different studies and providing arguments in favor of or against this concept to stimulate discussion and point out that experimental research is still needed to study the contribution of this assembly of microorganisms to the final product and to support or refute the concept.

Non-Saccharomyces Yeasts and Organic Wines Fermentation: Implications on Human Health

A relevant trend in winemaking is to reduce the use of chemical compounds in both the vineyard and winery. In organic productions, synthetic chemical fertilizers, pesticides, and genetically modified organisms must be avoided, aiming to achieve the production of a “safer wine”. Safety represents a big threat all over the world, being one of the most important goals to be achieved in both Western society and developing countries. An occurrence in wine safety results in the recovery of a broad variety of harmful compounds for human health such as amines, carbamate, and mycotoxins. The perceived increase in sensory complexity and superiority of successful uninoculated wine fermentations, as well as a thrust from consumers looking for a more “natural” or “organic” wine, produced with fewer additives, and perceived health attributes has led to more investigations into the use of non-Saccharomyces yeasts in winemaking, namely in organic wines. However, the use of copper and sulfur-based molecules as an alternative to chemical pesticides, in organic vineyards, seems to affect the composition of grape microbiota; high copper residues can be present in grape must and wine. This review aims to provide an overview of organic wine safety, when using indigenous and/or non-Saccharomyces yeasts to perform fermentation, with a special focus on some metabolites of microbial origin, namely, ochratoxin A (OTA) and other mycotoxins, biogenic amines (BAs), and ethyl carbamate (EC). These health hazards present an increased awareness of the effects on health and well-being by wine consumers, who also enjoy wines where terroir is perceived and is a characteristic of a given geographical area. In this regard, vineyard yeast biota, namely non-Saccharomyces wine-yeasts, can strongly contribute to the uniqueness of the wines derived from each specific region.

Lower-alcohol wines produced by Metschnikowia pulcherrima and Saccharomyces cerevisiae co-fermentations: The effect of sequential inoculation timing

In Latin, 'pulcherrima' is a superlative form of an adjective that translates as beautiful. Apart from being 'the most beautiful' yeast, Metschnikowia pulcherrima has a remarkable potential in production of wines with lower ethanol content. The oenological performance of six M. pulcherrima strains was hereby tested in sequential cultures with Saccharomyces cerevisiae. The best-performing strain MP2 was further characterised in fermentations with different S. cerevisiae inoculation delays in both white grape juice and Chemically Defined Grape Juice Medium (CDGJM). The analysis of main metabolites, undertaken prior to sequential inoculations and upon fermentation completion, highlighted metabolic interactions and carbon sinks other than ethanol in MP2 treatments. Depending on the inoculation delay, MP2 white wines contained between 0.6% and 1.2% (v/v) less ethanol than the S. cerevisiae monoculture, with even larger decreases detected in the CDGJM. The MP2 treatments also contained higher concentrations of TCA cycle by-products (i.e. fumarate and succinate) and glycerol, and lower concentrations of acetic acid. The analysis of volatile compounds showed increased production of acetate esters and higher alcohols in all MP2 wines, alongside other compositional alterations arising from the S. cerevisiae inoculation delay.