Genus Saccharomyces Research Articles

Влияние геотермальной воды в составе твердых сред культивирования на морфологические свойства дрожжей рода Saccharomyces

The influence of geothermal waters located on the territory of the city of Makhachkala (Republic of Dagestan), in the composition of solid cultivation media, on the cultural and morphological features of genus Saccharomyces yeast was studied. Changes in cell properties and the formation of specific parameters of giant yeast colonies S. cerevisiae Y-503, S. cerevisiae DAW-3a, S. oviformis M-12x have been established. For YPD and PD media, as a result of a series of experiments, optimal options were selected containing geothermal and distilled water in a ratio of 1:1 (well No. 36) and 2:1 (well No. 26). It was shown that the YPD medium was optimal for yeast growth, while in the population of the tetraploid Y-503 strain, the average cell size was slightly larger than cell strain M-12x and significantly exceeded the DAW-3a values. Installed that the use of diluted water from well No. 36 in the cultivation medium is most effective and leads to accelerated growth of yeast colonies. In the variant geothermal / distilled water, this indicator exceeded the control by 1.3 (Y-503, M-12x) times; in the variant with geothermal water without dilution - by 1.6 (Y-503) and 1.4 (M-12x) times. The cells of the S. cerevisiae Y-503 strain, regardless of the medium used, are characterized by the presence of various forms, including elongated ones; DAW-3a - exceptionally rounded; S. oviformis M-12x - rounded and oval shapes. A comparative analysis of the parameters of the colonies showed that all variants are characterized by a rounded shape, a radially striated surface; flat, with a convex center profile; light beige color and pasty, spreadable texture. As a result of our research, a modified nutrient medium PD has been developed - an agar for growing yeast, containing geothermal water from well No. 36 of the Makhachkala field as an additional source of mineral and organic compounds. The proposed composition of the medium is of interest for its further use in microbiological studies.

Effects of Saccharomyces cerevisiae on microbial community and flavor metabolites in solid-state fermentation of strong-flavor Baijiu

Targeted biofortification is an effective way to regulate the microbial community succession and the production of flavor metabolites in the Baijiu fermentation. However, the high organic acid present in the Baijiu brewing process causes the gradual succession of exogenous functional microorganisms to be less dominant, ultimately resulting in defective flavor substances. In this study, a strain of Saccharomyces cerevisiae YS219 with high production of ethyl hexanoate and excellent organic acid tolerance was excavated, and the effects of this strain on the microbial composition and flavor metabolites during the fermentation of strong-flavor Baijiu were investigated. The microbial community was analyzed using the Illumina Miseq Pe300 Sequencing Platform, and at the genus level, Saccharomyces, Lactobacillus, and Pediococcus became the dominant genera after biofortification. A total of 77 flavor substances were detected in the biofortified fermented grains, and the contents of total esters and alcohols increased significantly. Among them, ethanol and ethyl hexanoate were significantly increased. Mantel test showed significant positive correlation between lactic acid and Pediococcus. Moreover, lactic acid, acetic acid, and ethanol were negatively correlated with most of the fermenting microorganisms. Following inoculation with S. cerevisiae YS219, Saccharomyces and Pediococcus exhibited a positively significant link with ethyl hexanoate, according to Spearman's correlation analysis. Taken together, the results demonstrate that the addition of S. cerevisiae with excellent organic acid tolerance and high ethyl hexanoate production helps to promote the change of microbial community and the elevation of ethanol and ethyl hexanoate.

Auxotrophy-Independent Plasmid Shuttle Vectors for Applications in Diverse Yeasts

Plasmid shuttle vectors are a common tool used to study yeast physiology. The majority of yeast plasmids have been optimized for Saccharomyces cerevisiae lab strain compatibility, relying on auxotrophic complementation as their selective property. We sought to construct a series of plasmid shuttle vectors to extend functionality beyond strains with auxotrophic requirements, and test compatibility across a diverse panel of yeasts. We constructed 18 plasmids which were successfully maintained by yeasts from several genera. From a panel of 24 yeast strains, these plasmids were maintained by 18 yeasts, spanning 11 species within the genera Lachancea, Metschnikowia, Pichia, Saccharomyces, and Torulaspora. Additionally, an integrated gene expression reporter was assayed for functional compatibility with the 18 strains. Plasmid-derived gene expression was observed for 13 strains, spanning five species within the Saccharomyces genus, in addition to Torulaspora delbrueckii. These results indicate that this plasmid series is broadly useful for advancements and applications within academia, biotechnology, and the food and fermentation industries for research utilizing diverse Saccharomyces and non-Saccharomyces yeasts.

Fungal signature differentiates alcohol-associated liver disease from nonalcoholic fatty liver disease

ABSTRACT The fungal microbiota plays an important role in the pathogenesis of alcohol-associated liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD). In this study, we aimed to compare changes of the fecal fungal microbiota between patients with ALD and NAFLD and to elucidate patterns in different disease stages between the two conditions. We analyzed fungal internal transcribed spacer 2 (ITS2) sequencing using fecal samples from a cohort of 48 patients with ALD, 78 patients with NAFLD, and 34 controls. The fungal microbiota differed significantly between ALD and NAFLD. The genera Saccharomyces, Kluyveromyces, Scopulariopsis, and the species Candida albicans (C. albicans), Malassezia restricta (M. restricta), Scopulariopsis cordiae (S. cordiae) were significantly increased in patients with ALD, whereas the genera Kazachstania and Mucor were significantly increased in the NAFLD cohort. We identified the fungal signature consisting of Scopulariopsis, Kluyveromyces, M. restricta, and Mucor to have the highest discriminative ability to detect ALD vs NAFLD with an area under the curve (AUC) of 0.93. When stratifying the ALD and NAFLD cohorts by fibrosis severity, the fungal signature with the highest AUC of 0.92 to distinguish ALD F0-F1 vs NAFLD F0-F1 comprised Scopulariopsis, Kluyveromyces, Mucor, M. restricta, and Kazachstania. For more advanced fibrosis stages (F2-F4), the fungal signature composed of Scopulariopsis, Kluyveromyces, Mucor, and M. restricta achieved the highest AUC of 0.99 to differentiate ALD from NAFLD. This is the first study to identify a fungal signature to differentiate two metabolic fatty liver diseases from each other, specifically ALD from NAFLD. This might have clinical utility in unclear cases and might hence help shape treatment approaches. However, larger studies are required to validate this fungal signature in other populations of ALD and NAFLD.

Assess different fermentation characteristics of 54 lager yeasts based on group classification

Saccharomyces pastorianus, hybrids of Saccharomyces cerevisiae and Saccharomyces eubayanus, were generally regarded as authentic lager beer yeasts. In recent years, with more new findings of other Saccharomyces genus hybrids, yeasts used in lager beer brewing have been proved much more complicated than previous cognition. In this study, we analyzed the different fermentation characteristics of 54 yeast strains used for lager brewing in normal and very high gravity brewing based on group classification. The difference between Group Ⅰ and Group Ⅱ lager yeasts were more striking in very high gravity brewing. However, during our research progress, we realized that some yeasts used in this study were actually hybrids of S. cerevisiae and Saccharomyces kudriavzevii. Features of these hybrids could be beneficial to very high gravity brewing. We further discussed about the mechanism behind their outstanding characteristics and the reason why group classification methods of lager beer yeasts had limitations. Hybridization in yeasts is constantly getting richer. Lager yeasts could have more possibilities based on better understandings of their genetic background and roles of other Saccharomyces genus hybrids. Their heterosis shed light on innovation in brewing and other diverse fermentation industries.

Tracking alternative versions of the galactose gene network in the genus Saccharomyces and their expansion after domestication

Tracking alternative versions of the galactose gene network in the genus Saccharomyces and their expansion after domestication

Targeted 1−H-NMR wine analyses revealed specific metabolomic signatures of yeast populations belonging to the Saccharomyces genus

This study aimed to explore the non-volatile metabolomic variability of a large panel of strains (44) belonging to the Saccharomyces cerevisiae and Saccharomyces uvarum species in the context of the wine alcoholic fermentation. For the S. cerevisiae strains flor, fruit and wine strains isolated from different anthropic niches were compared. This phenotypic survey was achieved with a special focus on acidity management by using natural grape juices showing opposite level of acidity. A 1H NMR based metabolomics approach was developed for quantifying fifteen wine metabolites that showed important quantitative variability within the strains. Thanks to the robustness of the assay and the low amount of sample required, this tool is relevant for the analysis of the metabolomic profile of numerous wines. The S. cerevisiae and S. uvarum species displayed significant differences for malic, succinic, and pyruvic acids, as well as for glycerol and 2,3-butanediol production. As expected, S. uvarum showed weaker fermentation fitness but interesting acidifying properties. The three groups of S. cerevisiae strains showed different metabolic profiles mostly related to their production and consumption of organic acids. More specifically, flor yeast consumed more malic acid and produced more acetic acid than the other S. cerevisiae strains which was never reported before. These features might be linked to the ability of flor yeasts to shift their metabolism during wine oxidation.

Characterization of wild yeasts isolated from cereal sourdoughs and their potential for leavening wheat dough

Fermentation of cereal-made dough was the primary Ethiopian food for many years. Sourdough is believed to have many beneficial fermenting micro-floras depending on the source of dough and environmental conditions. The study aimed to isolate and characterize yeasts from fermenting cereal dough and evaluate their leavening potential for wheat dough. Morphological and biochemical characterizations such as sugar fermentation, glucose tolerance test, growth at different pH and temperatures, and agitation effect were employed to select potent yeasts. Accordingly, 16 potential yeast isolates were selected and subjected to further analysis. Finally, the yeasts were tested and compared for their leavening activity on the wheat dough at 37 °C and room temperature. Results revealed marvelous CO2 producer mesophile yeasts that degrade various sugars and tolerate up to 60% glucose concentration. The overall characterization assigned all the yeast isolates to the genus Saccharomyces and the Candida humilis. ANOVA showed that leavening activity by the yeast isolates was statistically higher at 37 °C compared to room temperature. The highest dough volume (6.2 mL) was recorded from Wh17, Wh5, and Ba12 isolates. Sor9 isolates were among the yeast that raised a minimum dough volume (0.7 mL). In contrast to commercial yeasts, the present study detected exceptional yeasts that matured within 24 h. Therefore, the discovered potential yeasts can be used for leavening dough in a short fermentation time and add aroma to baked products, making them a candidate in the baking industry. It could also be cost-effective as it could reduce media consumption and electricity utilization.

ISOLATION PROCESS OF ACID-PRODUCING BACTERIA WITH MODIFIED MEDIA TO OBTAIN ACETOBACTER ACETI IN CASSAVA (MANIHOT UTILISSIMA) FERMENTATION

Cassava (Manihot utilissima) is a type of high-carbohydrate plant that grows a lot in Indonesia. One of the most common and simple cassava processing is made into tape. One of the microorganisms in yeast is the genus Saccharomyces. Some species of this genus are considered very important in food production materials. One example is Saccharomyces cerevisiae, which is used in winemaking, bread, and beer. This study aims to: study the cassava fermentation process to obtain alcohol compounds as decomposition materials for acid-forming bacteria, knowing the characteristics of acid-forming bacteria in cassava tape fermentation, and getting isolates of Acetobacter aceti bacteria producing acetic acid in the cassava tape fermentation process. This research uses a qualitative descriptive method, with macroscopic, microscopic observations and gram painting on isolates of acid-forming bacteria that have been selected and successfully isolated from cassava fermentation. The results obtained by the colonies showed clear zones and did not show clear zones. Colonies that show clear zones are colonies that produce acid and react with carbonate ions; in the gram test obtained, a genus of bacteria obtained based on the results of isolation on cassava tape, namely some belonging to the genus Acetobacter with gram-negative (colored red) and some genus Lactobacillus with gram-positive (colored purple). The presence of a sour taste on the tape is caused by acid-forming bacteria after the presence of alcohol by the purples Saccharomyces cerevisiae.

Theromyzon maculosum (Rathke, 1862) as a vector of potentially pathogenic fungi in aquatic ecosystems

The aim of the study was to check the integument and alimentary tract of Theromyzon for the occurrence of fungi. Moreover, the mycological purity of water sources from which leeches were collected was analyzed. The potential role of the duck leech Theromyzon maculosum in transmitting pathogenic fungi has not been studied until now. Mycological analyses were performed according to the procedure approved in mycological diagnostic laboratories, using classical diagnostic methods (macro- and microcultures, microscopic observations). In total, 22 species of yeasts were detected. The specimens belong to eight genera: Candida, Citeromyces, Debaryomyces, Kluyveromyces, Lodderomyces, Pichia, Saccharomyces and Saccharomycodes. Overall, 18 species of fungi were isolated from leeches Theromyzon maculosum, including seven species from the integument and 11 species from the gastrointestinal system. Among fungi isolated from body integument, fungi of the genus Candida were dominant, whereas in the gastrointestinal system, the genus Saccharomyces dominated. From the river waters, nine fungi species were isolated, and yeasts of the genera Candida and Kluyveromyces dominated. Isolation of the same species of microfungi from the integument of leeches and the river water suggests that Theromyzon maculosum may be a potential vector of pathogenic yeasts for vertebrates living in the same ecosystems and for humans.

Presence of Saccharomyces eubayanus in fermentative environments reveals a new adaptive scenario in Patagonia.

Patagonia (Argentina and Chile) harbors the highest Saccharomyces eubayanus genomic diversity and its widest predominance in natural environments. In this work, S. eubayanus was isolated for the first time from a fermentative environment. This species was found dominating both a traditional apple chicha fermentation as well as feral apple trees in the Andean region of Aluminé (Argentina). S. eubayanus was the only Saccharomyces species found in the isolation substrates, although it coexisted with other non-Saccharomyces species. The absence of strong fermentative competitors of the Saccharomyces genus (like Saccharomyces uvarum or Saccharomyces cerevisiae) in the feral apples could promote the development and implantation of S. eubayanus in a spontaneous apple must fermentation. Phylogeographic analyses revealed a high intraspecific diversity in S. eubayanus, enabling the characterization of strains belonging to the genomic subpopulations PA1, PA2, and PB1 according to the sequences obtained for the intFR gene region. This result evidence that the studied sampling area represents a natural habitat for the species. Being a novel finding, studying the causes that allowed this species to prosper in a fermentative environment becomes essential. Hence, the physiological profile of the new isolates, including their ability to grow at different temperature, nitrogen, and ethanol concentrations was evaluated in comparison with a set of S. eubayanus strains previously isolated from natural environment and representing different genomic subpopulations. Greater physiological diversity was evidenced when strains isolated from both natural and fermentative environments were analyzed overall. Furthermore, no direct relationship between genomic population and physiological behavior was observed; on the opposite, strains appeared to exhibit similar behavior, primarily grouped by isolation origin.

Production of bioethanol from sweet sorghum [Sorghum bicolor L.] juice using yeast isolated from fermented sweet sorghum juice.

As a sugar-rich plant with no impact on global warming and food security, sweet sorghum can be exploited as an alternative source of renewable bioenergy. This study aimed to examine the potential of sweet sorghum juice for the generation of bioethanol using yeast isolated from the juice. The °Brix of sweet sorghum juice was measured using a digital refractometer. Additionally, 18 wild yeasts isolated from fermented sweet sorghum juice were subjected to various biochemical tests to describe them to identify potential yeast for ethanol production. The morphological and biochemical analyses of the yeasts revealed that all of the yeast isolates were most likely members of the genus Saccharomyces. The most ethanol-tolerant yeast isolate SJU14 was employed for sweet sorghum juice fermentation. A completely randomized factorial design was used with various fermentation parameters, primarily pH, temperature, and incubation period. Then ethanol content was determined using a potassium dichromate solution. According to the ANOVA, the highest ethanol content (18.765%) was produced at 30/26 °C, pH 4.5, and incubated for 96 h. Sweet sorghum juice was found to be an excellent source of potent yeasts, which have important industrial properties like the capacity to grow at high ethanol and glucose concentrations. Moreover, it can be utilized as a substitute substrate for the manufacturing of bioethanol production to lessen the environmental threat posed by fossil fuels. Further research is, therefore, recommended to develop strategically valuable applications of sweet sorghum for enhancing the food system and mitigating climate change.

Screening Ethanol-Producing Yeast Origin from Pineapple Honey Ananas comosus (L.) Merr var Quenn

The availability of fossil-based fuels will gradually decrease while the amount required increases. This has prompted research to find alternative energy sources, including bioethanol. Bioethanol, as an alternative energy source, can be used as a transportation fuel better than fossil-based fuels because ethanol has a high octane number, laminar velocity and heat of vaporisation. Meanwhile, the level of carbon and hydrocarbon emissions is low so it can increase combustion efficiency in vehicles. In addition, the use of bioethanol as fuel is environmentally friendly and renewable. Ethanol can be produced through a fermentation process using ethanol-producing yeast.  Pineapple honey is known for its high sugar and other nutrient content, so it is supposed that many types of yeast can grow well in it. This study aims to isolation and screening of bioethanol-producing yeast from Pineapple Honey. This study was carried out by yeast isolation method, primary yeast screening, secondary yeast screening, and characterisation of selected yeast isolates. Data on ethanol production by yeast isolates were analysed by ANOVA with α=0.05 using the R studio program. This primary isolation and screening phase found eight yeast isolates capable of fermenting glucose and producing acid and gas in the test medium. Test ethanol production in DPE medium with 18% glucose content on all isolates showed that all isolates could produce ethanol with a range of 4.20-10.35%. Isolates of IK4 showed the highest ethanol production ability (10.35%) (p<0.5%) in significant contrast to the other seven isolates. Based on macroscopic and microscopic morphological characterisations, IKM 4 isolates show similarities to the genus Saccharomyces
 Keywords: ethanol, pineapple, yeasts 

Analysis on driving factors of microbial community succession in Jiuyao of Shaoxing Huangjiu (Chinese yellow rice wine)

The microbial ecosystem of fermented food is greatly disturbed by human activities.Jiuyao is important saccharification starter for brewing huangjiu. The interaction between environmental factors and microorganisms significantly affected the microbial community structure at different stages of Jiuyao manufacturing. This study combined environmental factor analysis and high-throughput sequencing technology to comprehensively analyze the specific changes of microbial community and environmental factors in each fermentation stage of Jiuyao production and their correlation. The results showed that the activities of liquefaction enzyme, glycosylation enzyme and acid protease reached the highest value on the 8 th day (192 h) after the beginning of fermentation, and the cellulase activity reached the highest value at the end of fermentation. Pediococcus（37.5 %-58.2 %）, Weissella（9.2 %-27.0 %） and Pelomonas（0.1 %-12.1 %） were the main microbial genera in the genus bacteria, and Saccharomycopsis（37.1 %-52.0 %）, Rhizopus（12.5 %-31.0 %） and Saccharomyces（4.0 %-20.5 %） were the main microbial genera in the genus fungi. The results of correlation analysis showed that the microbial communities in Jiuyao were closely related to environmental factors. Most microbial communities were positively correlated with temperature, but negatively correlated with ambient humidity, CO2 concentration, acidity and water content of Jiuyao. In addition, the transcription levels of enzymes related to microbial glucose metabolism in Jiuyao were higher in the late stage of Jiuyao fermentation. Interestingly, these enzymes had high transcription levels in fungi such as Saccharomycopsis, Rhizopus and Saccharomyces, as well as in bacteria such as Pediococcus and Lactobacillus. This study provides a reference for revealing the succession rule of microbial community structure caused by environmental factors during the preparation of Jiuyao in Shaoxing Huangjiu.

Morphological characteristics of the duodenum of piglets fed with various feed additives

Early weaning of piglets from the sow and a sharp transition to granular feeding usually leads to the development of feed stress. As a consequence, changes occur in the small intestine epithelium, which are associated with desquamation of the epithelium of the villi, crypt hyperplasia and atrophy of the villi, colonization of pathogenic microflora, which leads to a decrease in digestion and absorption of nutrients. Hence the aim of this study was to evaluate the effect of various feed additives on the morphofunctional state of the duodenal mucosa of piglets in the pre-weaning period. Forty piglets of the same age were involved in the experiment, which were divided into four groups of 10 head each. The first group of piglets was a control one and received a standard diet and free access to water from the 7th day of life. Additionally to their standard diet, the piglets of group II were given a drug which included a combination of live yeast of the genus Saccharomyces and a complex of 6 enzymes (proteases, cellulases, xylanases, α-amylases, β-glucanases and phytases) in the amount of 0.5 kg/t of feed. Piglets of group III received 0.2 kg/t of a feed additive consisting of a mixture of essential oils from plant extracts. Piglets of group IV were given a supplement with dry yeast and egg powder enriched with immunoglobulins. Piglets had constant access to feed and water. On the 14th and 28th day of the experiment, three piglets from each group were euthanized in compliance with ethical standards for animals used in experiments. According to the results of histological studies, it was established that the duodenum mucous membrane in piglets of all experimental groups was characterized by insignificant variability. Mostly, the villi had a leaf-like or finger-like shape. The crypts were mostly closely adjacent to each other. The muscle layer was well developed, represented by smooth muscles that diverged in the places where the excretory ducts of Brunner's glands pass. The lamina of the mucous membrane was represented by a loose connective tissue made of collagen fibers and, to a lesser extent, elastic fibers and small capillaries between which lymphoid cellular elements were located. The enterocytes of the apical surface of the villi had a well-defined brush border and elongated nuclei that occupied a third of the cytoplasm. Morphometric studies showed that, compared to the control group of piglets, the addition of feed additives with a mixture of essential oils increased the taste and smell of the feed, contributing to its better consumption, thus having a positive effect on the condition of the mucous membrane. On the 14th and 28th day, a significant increase in the height and width of the villi was noted. In piglets that received feed supplements with a combination of live yeast, positive dynamics were also observed in terms of increasing the ratio of villi height to crypt depth. Summarizing the experiment results, we can note that various feed additives had a positive effect on the condition of the duodenum mucous membrane, but the feed additive containing a mixture of essential oils from plant extracts was more effective.

A novel aminotransferase gene and its regulator acquired in Saccharomyces by a horizontal gene transfer event

BackgroundHorizontal gene transfer (HGT) is an evolutionary mechanism of adaptive importance, which has been deeply studied in wine S. cerevisiae strains, where those acquired genes conferred improved traits related to both transport and metabolism of the nutrients present in the grape must. However, little is known about HGT events that occurred in wild Saccharomyces yeasts and how they determine their phenotypes.ResultsThrough a comparative genomic approach among Saccharomyces species, we detected a subtelomeric segment present in the S. uvarum, S. kudriavzevii, and S. eubayanus species, belonging to the first species to diverge in the Saccharomyces genus, but absent in the other Saccharomyces species. The segment contains three genes, two of which were characterized, named DGD1 and DGD2. DGD1 encodes dialkylglicine decarboxylase, whose specific substrate is the non-proteinogenic amino acid 2-aminoisobutyric acid (AIB), a rare amino acid present in some antimicrobial peptides of fungal origin. DGD2 encodes putative zinc finger transcription factor, which is essential to induce the AIB-dependent expression of DGD1. Phylogenetic analysis showed that DGD1 and DGD2 are closely related to two adjacent genes present in Zygosaccharomyces.ConclusionsThe presented results show evidence of an early HGT event conferring new traits to the ancestor of the Saccharomyces genus that could be lost in the evolutionary more recent Saccharomyces species, perhaps due to loss of function during the colonization of new habitats.

Revealing the influence of microbiota on the flavor of kombucha during natural fermentation process by metagenomic and GC-MS analysis

In this work, raw Pu-erh tea (RAPT) was employed for kombucha preparation, and the microbial composition and volatile flavor compounds of the fermented tea had been investigated during natural fermentation process. The head space-solid phase microextraction-gas chromatograph mass spectrometry (HS-SPME-GC-MS) was performed for volatiles analysis of unfermented tea and kombucha fermented for 3 days (KF-3) and 6 days (KF-6). Meanwhile, the microbial community of KF-3 and KF-6 were evaluated by metagenomic analysis. A total of 72 volatile compounds were identified and obvious changes in volatiles were observed during the fermentation process based on the results of GC-MS and principal component analysis (PCA). Metagenomic sequencing analysis demonstrated that bacterium Komagataeibacter saccharivorans and unclassified-g-komagataeibacter and yeast Saccharomyces cerevisiae and Brettanomyces bruxellensis were the most common microbes contained in the sampled kombucha communities. Furthermore, the relevance among microbial community and volatile compounds was evaluated through correlation heatmap analysis. The results suggested that the main flavor volatiles of kombucha (i.e., acids, esters and terpenes) were closely related to species of genus Komagataeibacter, Gluconacetobacter, Saccharomyces, Brettanomyces, Acetobacter, Novacetimonas and Pichia microorganisms. The obtained results would help to better understand microbial communities and volatile compounds of kombucha, which could provide useful information for enhancing the flavor quality of kombucha products.

Characterization of Aroma Active Compound Production during Kombucha Fermentation: Towards the Control of Sensory Profiles.

Since the sensorial profile is the cornerstone for the development of kombucha as a beverage with mass market appeal, advanced analytical tools are needed to gain a better understanding of the kinetics of aromatic compounds during the fermentation process to control the sensory profiles of the drink. The kinetics of volatile organic compounds (VOCs) was determined using stir bar sorptive extraction-gas chromatography-mass spectrometry, and odor-active compounds were considered to estimate consumer perception. A total of 87 VOCs were detected in kombucha during the fermentation stages. The synthesis of mainly phenethyl alcohol and isoamyl alcohol probably by Saccharomyces genus led to ester formation. Moreover, the terpene synthesis occurring at the beginning of fermentation (Δ-3-carene, α-phellandrene, γ-terpinene, m- and p-cymene) could be related to yeast activity as well. Principal component analysis identified classes that allowed the major variability explanation, which are carboxylic acids, alcohols, and terpenes. The aromatic analysis accounted for 17 aroma-active compounds. These changes in the evolution of VOCs led to flavor variations: from citrus-floral-sweet notes (geraniol and linalool domination), and fermentation brought intense citrus-herbal-lavender-bergamot notes (α-farnesene). Finally, sweet-floral-bready-honey notes dominated the kombucha flavor (2-phenylethanol). As this study allowed to estimate kombucha sensory profiles, an insight for the development of new drinks by controlling the fermentation process was suggested. Such a methodology should allow a better control and optimization of their sensory profile, which could in turn lead to greater consumer acceptance.

SO2-резистентность как критерий отбора штаммов Saccharomyces cerevisiae для органического виноделия

Sulfur dioxide is a popular conserving agent and antioxidant in winemaking. Unfortunately, it is bad for human health. Some yeast strains can reduce the dose of sulfur dioxide. Such yeasts should have good fermentation activity and dominate when inoculated into grape must. In addition, it should not synthesize sulfur dioxide and SO2-binding substances. The synthesis of sulfur dioxide and carbonyl compounds by yeast is related to the mechanisms of sulfur dioxide detoxification. The research objective was to study the relationship between the resistance of yeast to sulfur dioxide and its ability to synthesize sulfur dioxide and acetaldehyde during growth. 
 The study featured 17 yeast strains of the genus Saccharomyces. The yeasts were cultivated on grape must in a CGQ device until the stationary growth phase. The concentration of free and bound forms of sulfur dioxide was determined by titration, while that of aldehydes was determined by bisulfite method. The sulfite resistance of strains was measured ¬¬by the growth response of yeast cells to sulfur dioxide using CGQ technology. 
 Yeast strains differed in the degree of sulfur dioxide resistance. The samples were divided according to the increase in the lag phase time: by ≥ 8 h (sensitive), by 2–6 h, without changes (resistant). At Wilks L = 0.228 and α = 0.05, the sensitive cultures in a SO2-free medium had the highest value of minimal generation time in the exponential growth phase (5.3 ± 2.1 h). The resistant samples demonstrated the highest synthesis of acetaldehyde (54.7 ± 11.1 mg/L) and sulfur dioxide (21.0 ± 10.3 mg/L). The second group cultures had the lowest content of SO2-bound forms in the medium (10.9 ± 4.2 mg/L) and were in an interposition in terms of other indicators. 
 The time it takes a yeast strain to adapt to sulfur dioxide can be used as a parameter for the primary culture selection in eco-winemaking. According to the physiological and biochemical profile, the resistant strains can be recommended for the production of SO2-low wines, while the samples from the second test group proved optimal for organic wines. Further research will expand the range of yeast strains and their indicators.

Beyond S. cerevisiae for winemaking: Fermentation-related trait diversity in the genus Saccharomyces

Saccharomyces cerevisiae is the yeast of choice for most inoculated wine fermentations worldwide. However, many other yeast species and genera display phenotypes of interest that may help address the environmental and commercial challenges the wine industry has been facing in recent years. This work aimed to provide, for the first time, a systematic phenotyping of all Saccharomyces species under winemaking conditions. For this purpose, we characterized the fermentative and metabolic properties of 92 Saccharomyces strains in synthetic grape must at two different temperatures. The fermentative potential of alternative yeasts was higher than expected, as nearly all strains were able to complete fermentation, in some cases more efficiently than commercial S. cerevisiae strains. Various species showed interesting metabolic traits, such as high glycerol, succinate and odour-active compound production, or low acetic acid production, compared to S. cerevisiae. Altogether, these results reveal that non-cerevisiae Saccharomyces yeasts are especially interesting for wine fermentation, as they may offer advantages over both S. cerevisiae and non-Saccharomyces strains. This study highlights the potential of alternative Saccharomyces species for winemaking, paving the way for further research and, potentially, for their industrial exploitation.