Isolation of indigenous Saccharomyces cerevisiae strains isolated of fermented must from wine grapes in a tropical semiarid region of Brazil

The present study aimed to isolate, identify and characterize the yeasts of fermented must from grapes in the São Francisco Valley region, Brazil. The grapes were collected from four vineyards in the region and taken to the laboratory for must production and strain isolation. The yeasts were identified by sequencing the D1/D2 variable domains of the largest subunit of the rRNA gene. The Saccharomyces cerevisiae strains were differentiated using the mitochondrial DNA restriction technique (RFLP-mtDNA), and compared with the commercial strains used in the region for wine production. A total of 368 yeasts were isolated, 109 of which were non-Saccharomyces and 259 S. cerevisiae. Of these, 184 were indigenous and 75 commercial varieties. Among the indigenous strains, 22 RFLP-mtDNA and two commercial profiles were characterized. The must of the samples collected was appropriate substrate for identifying and isolating the non-Saccharomyces and S. cerevisiae strains and commercial yeasts. Given that the indigenous strains were more numerous than their commercial counterparts, which were selected in countries with a temperate climate, new studies should be conducted, testing the capacity of indigenous yeasts in producing quality wines, with typicality and regional identity, some of which may become commercially viable.

Genotyping and Phenotyping of Indigenous Saccharomyces cerevisiae from a New Zealand Organic Winery and Commercial Sources Using Inter-Delta and MALDI-TOF MS Typing

We used inter-delta typing (IDT) and MALDI-TOF profiling to characterize the genetic and phenotypic diversity of 45 commercially available winemaking Saccharomyces cerevisiae strains and 60 isolates from an organic winemaker from Waipara, New Zealand, as a stratified approach for predicting the commercial potential of indigenous isolates. A total of 35 IDTs were identified from the commercial strains, with another 17 novel types defined among the Waipara isolates. IDT 3 was a common type among strains associated with champagne production, and the only type in commercial strains also observed in indigenous isolates. MALDI-TOF MS also demonstrated its potential in S. cerevisiae typing, particularly when the high-mass region (m/z 2000-20,000) was used, with most indigenous strains from each of two fermentation systems distinguished. Furthermore, the comparison between commercial strains and indigenous isolates assigned to IDT 3 revealed a correlation between the low-mass data (m/z 500-4000) analysis and the recommended use of commercial winemaking strains. Both IDT and MALDI-TOF analyses offer useful insights into the genotypic and phenotypic diversity of S. cerevisiae, with MALDI-TOF offering potential advantages for the prediction of applications for novel, locally isolated strains that may be valuable for product development and diversification.

Biodiversity and brewing attitude of non-Saccharomyces strains isolated from Uruguayan vineyards and other ecosystems

In recent years, interest in non-Saccharomyces yeasts for the innovation and development of different and alternative beer styles has been increasing, especially for the microbrewing industry. This work studied the biodiversity of non-Saccharomyces yeasts based on isolates from grapes of different Uruguayan vineyards, craft breweries and raw materials, with the aim of selecting autochthonous non-Saccharomyces yeasts with a brewing attitude. Brewing tests were performed on synthetic wort developed for this purpose, and the evolution of alcoholic fermentation was monitored by measuring glucose, maltose, maltotriose consumption, ethanol and glycerol production and final sensory analysis. A total of two hundred seventy-one yeast strains belonging to different genera were evaluated according to these parameters. After evaluating alcoholic fermentation performance, a native yeast strain belonging to the species Starmerella meliponinorum was selected due to its high maltotriose consumption and glycerol production, making it a very promising brewing yeast, especially for production of low carbohydrate beers.

Indigenous Saccharomyces cerevisiae Could Better Adapt to the Physicochemical Conditions and Natural Microbial Ecology of Prince Grape Must Compared with Commercial Saccharomyces cerevisiae FX10

Indigenous Saccharomyces cerevisiae, as a new and useful tool, can be used in fermentation to enhance the aroma characteristic qualities of the wine-production region. In this study, we used indigenous S. cerevisiae L59 and commercial S. cerevisiae FX10 to ferment Prince (a new hybrid variety from Lion Winery) wine, detected the basic physicochemical parameters and the dynamic changes of fungal communities during fermentation, and analyzed the correlations between fungal communities and volatile compounds. The results showed that the indigenous S. cerevisiae L59 could quickly adapt to the specific physicochemical conditions and microbial ecology of the grape must, showing a strong potential for winemaking. Compared with commercial S. cerevisiae FX10, the wine fermented by indigenous S. cerevisiae L59 contained more glycerol and less organic acids, contributing to a rounder taste. The results of volatile compounds indicated that the indigenous S. cerevisiae L59 had a positive effect on adding rosy, honey, pineapple and other sweet aroma characteristics to the wine. Overall, the study we performed showed that selection of indigenous S. cerevisiae from the wine-producing region as a starter for wine fermentation is conducive to improving the aroma profile of wine and preserving the aroma of the grape variety.

Wine yeast selection in the Iberian Peninsula: Saccharomyces and non-Saccharomyces as drivers of innovation in Spanish and Portuguese wine industries

Yeast selection for the wine industry in Spain started in 1950 for the understanding of the microbial ecology, and for the selection of optimal strains to improve the performance of alcoholic fermentation and the overall wine quality. This process has been strongly developed over the last 30 years, firstly on Saccharomyces cerevisiae, and, lately, with intense activity on non-Saccharomyces. Several thousand yeast strains have been isolated, identified and tested to select those with better performance and/or specific technological properties. The present review proposes a global survey of this massive ex-situ preservation of eukaryotic microorganisms, a reservoir of biotechnological solutions for the wine sector, overviewing relevant screenings that led to the selection of strains from 12 genera and 22 species of oenological significance. In the first part, the attention goes to the selection programmes related to relevant wine-producing areas (i.e. Douro, Extremadura, Galicia, La Mancha and Uclés, Ribera del Duero, Rioja, Sherry area, and Valencia). In the second part, the focus shifted on specific non-Saccharomyces genera/species selected from different Spanish and Portuguese regions, exploited to enhance particular attributes of the wines. A fil rouge of the dissertation is the design of tailored biotechnological solutions for wines typical of given geographic areas.

Growth of Non-Saccharomyces Native Strains under Different Fermentative Stress Conditions

The selection of yeast strains adapted to fermentation stresses in their winegrowing area is a key factor to produce quality wines. Twelve non-Saccharomyces native strains from Denomination of Origin (D.O.) “Vinos de Madrid” (Spain), a warm climate winegrowing region, were tested under osmotic pressure, ethanol, and acidic pH stresses. In addition, mixed combinations between non-Saccharomyces and a native Saccharomyces cerevisiae strain were practised. Phenotypic microarray technology has been employed to study the metabolic output of yeasts under the different stress situations. The yeast strains, Lachancea fermentati, Lachancea thermotolerans, and Schizosaccharomyces pombe showed the best adaptation to three stress conditions examined. The use of mixed cultures improved the tolerance to osmotic pressure by Torulaspora delbrueckii, S. pombe, and Zygosaccharomyces bailii strains and to high ethanol content by Candida stellata, S. pombe, and Z. bailii strains regarding the control. In general, the good adaptation of the native non-Saccharomyces strains to fermentative stress conditions makes them great candidates for wine elaboration in warm climate areas.

Biodiversity and oenological attitude of Saccharomyces cerevisiae strains isolated in the Montalcino district: biodiversity of S. cerevisiae strains of Montalcino wines

The biodiversity of Saccharomyces cerevisiae was studied in the Montalcino area (Italy). Two wineries were involved in the study, which compared the genotypic and oenological characteristics of the S. cerevisiae strains isolated in spontaneous fermentations. After isolation yeasts were identified by 26S rRNA gene sequence analysis, and S. cerevisiae strains were characterized through interdelta sequence analysis (ISA). Oenological tests were performed in synthetic grape must by varying the magnitude of the main wine-imiting factors. The evolution of alcoholic fermentation was monitored by measuring sugar consumption and flow cytometry. The results revealed the prevalence of S. cerevisiae from the third day of fermentation and the presence of a wide range of S. cerevisiae strains having ISA profiles characteristic of each winery. From an oenological point of view, the features of such strains, in terms of resistance to wine-limiting factors, seemed to be linked to the main oenological variables applied in the production process of each winery. Extreme fermentation temperatures and copper residues are the variables that mostly depress the yeast population, in terms of fermentation rate and cell viability. Flow cytometry revealed the different impact of limiting factors on the viability of yeast by the quantification of the ratio between live/dead yeast cells of each strain, suggesting different mechanisms of inhibition, for instance stuck of cell growth or cell killing, in response to the different stress factors.

Selection of Indigenous Saccharomyces cerevisiae Strains and Exploitation of a Pilot-Plant to Produce Fresh Yeast Starter Cultures in a Winery

The inoculation of grape juice with Saccharomyces cerevisiae strains selected from indigenous yeast populations can be a suitable tool to control alcoholic fermentation, contributing to producing wines with typical flavor and aroma and, hence, the demand for native starter cultures is increasing. However, since low amounts of indigenous yeast biomasses are usually required for local winemaking, the industrial production of these yeasts can be expensive. Therefore, in this study, after selecting an indigenous S. cerevisiae strain based on relevant oenological and technological features, a pilot-plant for easy and rapid production of fresh yeast biomass directly in a winery located in Tuscany, was exploited. The selected yeast strain was used as a starter to carry out 25 and 100 hL fermentations and its enological performance was compared with that of the commercial starter normally used in the winery. Chemical and sensory analysis of the resulting wines showed that they differentiated according to the used yeast strain, with the wines produced by the indigenous S. cerevisiae strain being characterized by a distinctive aromatic and sensory profile. In conclusion, the pilot-plant effectively resulted in producing fresh yeast starter cultures in the winery to be successfully used to carry out alcoholic fermentations.

Marker Assisted Selection of Malic-Consuming Saccharomyces cerevisiae Strains for Winemaking. Efficiency and Limits of a QTL's Driven Breeding Program

Natural Saccharomyces cerevisiae yeast strains exhibit very large genotypic and phenotypic diversity. Breeding programs that take advantage of this characteristic are widely used for selecting starters for wine industry, especially in the recent years when winemakers need to adapt their production to climate change. The aim of this work was to evaluate a marker assisted selection (MAS) program to improve malic acid consumption capacity of Saccharomyces cerevisiae in grape juice. Optimal individuals of two unrelated F1-hybrids were crossed to get a new genetic background carrying many "malic consumer" loci. Then, eleven quantitative trait loci (QTLs) already identified were used for implementing the MAS breeding program. By this method, extreme individuals able to consume more than 70% of malic acid in grape juice were selected. These individuals were tested in different enological matrixes and compared to their original parental strains. They greatly reduced the malic acid content at the end of alcoholic fermentation, they appeared to be robust to the environment, and they accelerated the ongoing of malolactic fermentations by Oenococcus oeni. This study illustrates how MAS can be efficiently used for selecting industrial Saccharomyces cerevisiae strains with outlier properties for winemaking.

Non-Saccharomyces Commercial Starter Cultures: Scientific Trends, Recent Patents and Innovation in the Wine Sector

For 15 years, non-Saccharomyces starter cultures represent a new interesting segment in the dynamic field of multinationals and national companies that develop and sell microbial-based biotechnological solutions for the wine sector. Although the diversity and the properties of non- Saccharomyces species/strains have been recently fully reviewed, less attention has been deserved to the commercial starter cultures in term of scientific findings, patents, and their innovative applications. Considering the potential reservoir of biotechnological innovation, these issues represent an underestimated possible driver of coordination and harmonization of research and development activities in the field of wine microbiology. After a wide survey, we encompassed 26 different commercial yeasts starter cultures formulated in combination with at least one non-Saccharomyces strain. The most recent scientific advances have been explored delving into the oenological significance of these commercial starter cultures. Finally, we propose an examination of patent literature for the main yeasts species commercialised in non-Saccharomyces based products. We highlight the presence of asymmetries among scientific findings and the number of patents concerning non-Saccharomyces-based commercial products for oenological purposes. Further investigations on these microbial resources might open new perspectives and stimulate attractive innovations in the field of wine-making biotechnologies.

Dominance of S. cerevisiae Commercial Starter Strains during Greco di Tufo and Aglianico Wine Fermentations and Evaluation of Oenological Performances of Some Indigenous/Residential Strains

In order to evaluate dominance/implantation of starter cultures for wine fermentation, both commercial starters and wild strains were monitored during the fermentation of Greco di Tufo (GR) and Aglianico of Taurasi (AGL) musts. Preliminary characterization of commercial strains was carried out by several molecular markers. Five fermentations—four starter-inoculated and one spontaneous—were carried out in duplicates by using grapes from GR and AGL. Trials were monitored, and yeast cultures were isolated within the dominant microflora. Comparison of Interdelta patterns allowed to assess the real occurrence of both starters and indigenous strains. A high genetic diversity within S. cerevisiae strains was detected. In starter-led fermentations (except for few cases), in addition to the starter strains, indigenous S. cerevisiae biotypes were found, as well. Native strains isolated from replicates of the same fermentation showed different genetic profiles. Spontaneous fermentations were conducted, during the first 5 days, by non-Saccharomyces yeasts and, afterwards, by a high number (16 in the AGL and 20 in the GR) of S. cerevisiae biotypes. Indigenous biotypes isolated by GR revealed a high variability in oenological features and, in several cases, showed better performances than those recorded for commercial strains. The study further highlighted the low dominance of some commercial starter cultures. Moreover, autochthonous yeast strains proved to be sometimes more aggressive in terms of fermentation vigor in GR must, likely because better adapted to ecological and technological conditions occurring during winemaking. Finally, the use of such strains for production of autochthonous “pied de cuve” may be a useful strategy for lowering production cost of winemaking.

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 impact of active dry yeasts in commercial wineries from the Denomination of Origen "Vinos de Madrid", Spain

This paper has studied the success of implantation for 16 commercial active dry yeasts (ADYs) during industrial fermentation (30) and the impact of these yeasts during spontaneous fermentations (19) in 10 wineries from the Denomination of Origin "Vinos de Madrid" over two consecutive years. Yeasts strains were identified by molecular techniques, pulsed field electrophoresis and microsatellite analysis. According to these techniques, all the ADYs were different with the exceptions of two strains, L2056 and Rh, which showed the same karyotype and loci size. The results showed that inoculating fermentations with ADYs did not ensure their dominance throughout the fermentation; the implantation level of ADYs was above 80% in only 9 of the 30 commercial fermentations studied; while in 16 fermentations, the dominance of the inoculated ADYs was below 50%. The type of vinification with the best implantation results overall were those associated with red wine fermentations. ADYs affected spontaneous fermentations, although their impact was observed to decrease in the second year of the study. Therefore, specific adaptation studies are necessary before using commercial yeasts during the fermentation process. At the same time, a study was carried out on the frequency of commercial strains in IMIDRA's yeast collection, made up of strains isolated from spontaneous fermentations of the different areas and cellars since the beginning of the Denomination of Origin "Vinos de Madrid" in 1990. Six different ADYs were found with a frequency of less than 5%.

The Influence of Selected Autochthonous Saccharomyces cerevisiae Strains on the Physicochemical and Sensory Properties of Narince Wines

Vitis vinifera cv. Narince is a Turkish native white grape variety. In this study, volatile and sensory properties of Narince wines that are produced with autochthonous Saccharomyces cerevisiae (S. cerevisiae) strains and commercial strain were compared. Autochthonous yeast strains 1044 (MG017575), 1088 (MG017577), and 1281 (MG017581) were previously isolated from spontaneous fermentations of Narince grapes. Volatile compounds formed in wines were extracted using a liquid–liquid extraction method and determined by GC-MS-FID. All yeast strains fermented Narince grape juice to dryness. The differences between the volatile profiles of the yeast strains were determined. Wines fermented with autochthonous strains 1281 and 1044 produced a higher amount of acetates and ethyl esters. While the highest concentrations of ethyl hexanoate and hexyl acetate were found in wine fermented with 1044, the highest concentrations of ethyl octanoate, ethyl decanoate, isoamyl acetate, and 2-phenylethyl acetate were found in wine fermented with strain 1281. Also, the highest contents of 2-phenyl ethanol and linalool were found in wine fermented with strain 1281. According to sensory analysis, the wine fermented with 1281 achieved the best scores in floral and fruity attributes, as well as balance and global impression. The data obtained in the present study showed that autochthonous yeast strains affect the final physicochemical composition and sensory profile of Narince wines.

The Different Physical and Chemical Composition of Grape Juice and Marc Influence Saccharomyces cerevisiae Strains Distribution During Fermentation

During white-grape winemaking, grape marc is separated from juice immediately after crushing. Both mark and juice are obtained from the same grapes, but they differ strongly for their physical and chemical properties. Marc is mainly composed of solid residues. Its pH is usually higher than that of the juice and Saccharomyces cerevisiae strains are largely present. Therefore, it can be considered as a potential alternative environment for the selection of industrial yeasts. In order to evaluate the effect of different pH and physical state of the two matrices on grapes yeast population composition, the isolation of S. cerevisiae, from both grape juice and marc during simultaneous fermentations, was performed. After yeast identification and genotyping, strains present at high frequencies were tested in fermentation at different pH values. Biofilm production was also tested to evaluate strain ability to develop on a solid matrix. Genotype analysis showed that high-frequency strains were always more abundant in one of the two environments, suggesting the existence of a selective effect. Generally, fermentations at different pH revealed that the best fermentation performance of each strain, in terms of CO₂ production, was in the pH range of its original environment. Only one strain, mostly present in grape marc, produced a high biofilm level. Therefore, biofilm production does not seem to favor strain adaptation to grape marc condition.

PRACTICAL APPLICATION

These results demonstrate that grape juice and marc represent two different environments able to influence yeast strains distribution. The pH level can be included among the selection factors acting on yeast strains distribution. Grape marc can be considered a yeasts reservoir and its fermentation can be used for the development and isolation of new strains, genetically and physiologically different from those present in the grape juice.

Sequential Inoculation of Native Non-Saccharomyces and Saccharomyces cerevisiae Strains for Wine Making

The use of non-Saccharomyces yeast for wine making is becoming a common trend in many innovative wineries. The application is normally aimed at increasing aromas, glycerol, reducing acidity, and other improvements. This manuscript focuses on the reproduction of the native microbiota from the vineyard in the inoculum. Thus, native selected yeasts (Hanseniaspora uvarum, Metschnikowia pulcherrima, Torulaspora delbrueckii, Starmerella bacillaris species and three different strains of Saccharomyces cerevisiae) were inoculated sequentially, or only S. cerevisiae (three native strains together or one commercial) was used. Inoculations were performed both in laboratory conditions with synthetic must (400 mL) as well as in industrial conditions (2000 kg of grapes) in red winemaking in two different varieties, Grenache and Carignan. The results showed that all the inoculated S. cerevisiae strains were found at the end of the vinifications, and when non-Saccharomyces yeasts were inoculated, they were found in appreciable populations at mid-fermentation. The final wines produced could be clearly differentiated by sensory analysis and were of similar quality, in terms of sensory analysis panelists' appreciation.

Use of Torulaspora delbrueckii and Saccharomyces cerevisiae in semi-industrial sequential inoculation to improve quality of Palomino and Chardonnay wines in warm climates

AIMS

We have evaluated for the first time the impact of two commercial yeast strains (Torulaspora delbrueckii TD291 and Saccharomyces cerevisiae QA23) inoculated sequentially in musts of Chardonnay and Palomino Fino grape varieties grown under warm climate (South-west of Spain).

METHODS AND RESULTS

Semi-industrial scale alcoholic fermentations (AF) were performed during the 2011 and 2012 harvests. Implantation analyses demonstrated that T. delbrueckii is the predominant strain until the end of the AF phase. Wines with sequential inoculation (SI) resulted in the production of low levels of acetic acid (which gives wine an undesirable 'vinegary' character), low acetaldehyde in Chardonnay and high in Palomino wines. The most salient attributes that contribute to the quality of the Chardonnay and Palomino wines produced were aroma intensity, fresh and tropical fruit character.

CONCLUSIONS

This study demonstrated that SI of T. delbrueckii and S. cerevisiae contribute significantly to the improvement of Chardonnay wine aromas and the creation of new styles of wine for Palomino.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has generated new knowledge about the biotechnological potential of T. delbrueckii (TD219) and S. cerevisiae (QA23) for improving the organoleptic properties of Chardonnay and Palomino wines.

A Focus on Quality and Safety Traits of Saccharomyces cerevisiae Isolated from Uva di Troia Grape Variety

The aim of this work was to study Saccharomyces cerevisiae strains isolated from vineyards of the autochthonous grape variety "Uva di Troia" located in different geographical areas of Apulian region (Southern Italy). Four hundred isolates were studied in relation to H₂ S production, β-glucosidase activity, and pigments adsorption from grape skin. Thus, 81 isolates were selected, identified through the amplification of the interdelta region, and grouped in 19 biotypes (from I to XIX). The enological performances were assessed to determine the content of residual sugars, ethanol, glycerol, and volatile acidity, after a microfermentation in Uva di Troia must for each isolate. The ability to remove ochratoxin A (OTA) was studied as an additional tool to select promising strains. A geographical-dependent technological variability was found for glycerol and volatile acidity, suggesting that the different indigenous yeasts can have a peculiar impact on the final characteristics of the corresponding wine ("Nero di Troia"). Only 2 biotypes (VI and XVII) were able to remove OTA throughout fermentation, with the highest reduction achieved by the biotype XVII (ca. 30%).

Rapid and not culture-dependent assay based on multiplex PCR-SSR analysis for monitoring inoculated yeast strains in industrial wine fermentations

Wine industry needs a simple method for rapid diagnosis of the dominance of inoculated strains that could be performed routinely during the fermentation process. We present a suitable, high-throughput, and low-cost method to monitor rapidly the dominance of inoculated yeast strains in industrial fermentations of red and white wines using an activated carbon cleaning pretreatment, and a rapid DNA extraction method plus multiplex PCR-SSR analysis. We apply this technique directly to samples of fermenting wines without previously isolating yeast colonies. Results are obtained in a maximum time of 4.5 h.

Technological properties of indigenous wine yeast strains isolated from wine production regions of Turkey

The purpose of this study was to evaluate the important technological and fermentative properties of wine yeast strains previously isolated from different wine producing regions of Turkey. The determination of the following important properties was made: growth at high temperatures; fermentative capability in the presence of high sugar concentration; fermentation rate; hydrogen sulfide production; killer activity; resistance to high ethanol and sulfur dioxide; foam production; and enzymatic profiles. Ten local wine yeast strains belonging to Saccharomyces, and one commercial active dry yeast as a reference strain were evaluated. Fermentation characteristics were evaluated in terms of kinetic parameters, including ethanol yield (YP/S), biomass yield (YX/S), theoretical ethanol yield (%), specific ethanol production rate (qp; g/gh), specific glucose uptake rate (qs; g/gh), and the substrate conversion (%). All tested strains were able to grow at 37 °C and to start fermentation at 30° Brix, and were resistant to high concentrations of sulfur dioxide. 60 % of the strains were weak H2S producers, while the others produced high levels. Foam production was high, and no strains had killer activity. Six of the tested strains had the ability to grow and ferment at concentrations of 14 % ethanol. Except for one strain, all fermented most of the media sugars at a high rate, producing 11.0-12.4 % (v/v) ethanol. Although all but one strain had suitable characteristics for wine production, they possessed poor activities of glycosidase, esterase and proteinase enzymes of oenological interest. Nine of the ten local yeast strains were selected for their good oenological properties and their suitability as a wine starter culture.

Molecular and Technological Characterization of Saccharomyces cerevisiae Strains Isolated from Natural Fermentation of Susumaniello Grape Must in Apulia, Southern Italy

The characterization of autochthonous Saccharomyces cerevisiae strains is an important step towards the conservation and employment of microbial biodiversity. The utilization of selected autochthonous yeast strains would be a powerful tool to enhance the organoleptic and sensory properties of typical regional wines. In fact, indigenous yeasts are better tailored to a particular must and because of this they are able to praise the peculiarities of the derived wine. The present study described the biodiversity of indigenous S. cerevisiae strains isolated from natural must fermentations of an ancient and recently rediscovered Apulian grape cultivar, denoted as "Susumaniello." The yeast strains denoted by the best oenological and technological features were identified and their fermentative performances were tested by either laboratory assay. Five yeast strains showed that they could be excellent candidates for the production of industrial starter cultures, since they dominated the fermentation process and produced wines characterized by peculiar oenological and organoleptic features.

Biodiversity and safety aspects of yeast strains characterized from vineyards and spontaneous fermentations in the Apulia Region, Italy

This work is the first large-scale study on vineyard-associated yeast strains from Apulia (Southern Italy). Yeasts were identified by Internal Transcribed Spacer (ITS) ribotyping and bioinformatic analysis. The polymorphism of interdelta elements was used to differentiate Saccharomyces cerevisiae strains. Twenty different species belonging to 9 genera were identified. Predominant on the grape surface were Metschnikowia pulcherrima, Hanseniaspora uvarum and Aureobasidium pullulans, whereas M. pulcherrima and H. uvarum were dominant in the early fermentation stage. A total of 692 S. cerevisiae isolates were identified and a number of S. cerevisiae strains, ranging from 26 to 55, was detected in each of the eight fermentations. The strains were tested for biogenic amines (BAs) production, either in synthetic media or grape must. Two Pichia manshurica, an Issatchenkia terricola and a M. pulcherrima strains were able to produce histamine and cadaverine, during must fermentation. The production of BAs in wine must was different than that observed in the synthetic medium. This feature indicate the importance of an "in grape must" assessment of BAs producing yeast. Overall, our results suggest the importance of microbiological control during wine-making to reduce the potential health risk for consumer represented by these spoilage yeasts.

Genetic diversity and population structure of Saccharomyces cerevisiae strains isolated from different grape varieties and winemaking regions

We herein evaluate intraspecific genetic diversity of fermentative vineyard-associated S. cerevisiae strains and evaluate relationships between grape varieties and geographical location on populational structures. From the musts obtained from 288 grape samples, collected from two wine regions (16 vineyards, nine grape varieties), 94 spontaneous fermentations were concluded and 2820 yeast isolates were obtained that belonged mainly (92%) to the species S. cerevisiae. Isolates were classified in 321 strains by the use of ten microsatellite markers. A high strain diversity (8-43 strains per fermentation) was associated with high percentage (60-100%) of fermenting samples per vineyard, whereas a lower percentage of spontaneous fermentations (0-40%) corresponded to a rather low strain diversity (1-10 strains per fermentation).For the majority of the populations, observed heterozygosity (Ho) was about two to five times lower than the expected heterozygosity (He). The inferred ancestry showed a very high degree of admixture and divergence was observed between both grape variety and geographical region. Analysis of molecular variance showed that 81-93% of the total genetic variation existed within populations, while significant differentiation within the groups could be detected. Results from AMOVA analysis and clustering of allelic frequencies agree in the distinction of genetically more dispersed populations from the larger wine region compared to the less extended region. Our data show that grape variety is a driver of populational structures, because vineyards with distinct varieties harbor genetically more differentiated S. cerevisiae populations. Conversely, S. cerevisiae strains from vineyards in close proximity (5-10 km) that contain the same grape variety tend to be less divergent. Populational similarities did not correlate with the distance between vineyards of the two wine regions. Globally, our results show that populations of S. cerevisiae in vineyards may occur locally due to multi-factorial influences, one of them being the grape variety.

Computational approaches for the genetic and phenotypic characterization of a Saccharomyces cerevisiae wine yeast collection

Within this study, we have used a set of computational techniques to relate the genotypes and phenotypes of natural populations of Saccharomyces cerevisiae, using allelic information from 11 microsatellite loci and results from 24 phenotypic tests. A group of 103 strains was obtained from a larger S. cerevisiae winemaking strain collection by clustering with self-organizing maps. These strains were further characterized regarding their allelic combinations for 11 microsatellites and analysed in phenotypic screens that included taxonomic criteria (carbon and nitrogen assimilation tests, growth at different temperatures) and tests with biotechnological relevance (ethanol resistance, H(2)S or aromatic precursors formation). Phenotypic variability was rather high and each strain showed a unique phenotypic profile. The results, expressed as optical density (A(640)) after 22 h of growth, were in agreement with taxonomic data, although with some exceptions, since few strains were capable of consuming arabinose and ribose to a small extent. Based on microsatellite allelic information, naïve Bayesian classifier correctly assigned (AUC = 0.81, p < 10(-8)) most of the strains to the vineyard from where they were isolated, despite their close location (50-100 km). We also identified subgroups of strains with similar values of a phenotypic feature and microsatellite allelic pattern (AUC > 0.75). Subgroups were found for strains with low ethanol resistance, growth at 30 degrees C and growth in media containing galactose, raffinose or urea. The results demonstrate that computational approaches can be used to establish genotype-phenotype relations and to make predictions about a strain's biotechnological potential.

Genetic analysis of Saccharomyces cerevisiae strains isolated from palm wine in eastern Nigeria. Comparison with other African strains

AIMS

To study the yeast diversity of Nigerian palm wines by comparison with other African strains.

METHODS AND RESULTS

Twenty-three Saccharomyces cerevisiae strains were obtained from palm wine samples collected at four locations in eastern Nigeria, and characterized using different molecular techniques: internal transcribed spacer restriction fragment length polymorphism and sequence analysis, pulsed field gel electrophoresis, inter delta typing and microsatellite multilocus analysis. These techniques revealed that palm wine yeasts represent a group of closely related strains that includes other West African isolates (CBS400, NCYC110, DVPG6044). Population analysis revealed an excess of homozygote strains and an allelic richness similar to wine suggestive of local domestication. Several other African yeast strains were not connected to this group. Ghana sorghum beer strains and other African strains (DBVPG1853 and MUCL28071) displayed strikingly high relatedness with European bread, beer or wine strains, and the genome of strain MUCL30909 contained African and wine-type alleles, indicating its hybrid origin.

CONCLUSIONS

Nigerian palm wine yeast represents a local specific yeast flora, whereas a European origin or hybrid was suspected for several other Africa isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study presents the first genetic characterization of an autochthonous African palm wine yeast population and confirms the idea that human intervention has favoured yeast migration.

23S RNA-derived replicon as a 'molecular tag' for monitoring inoculated wine yeast strains

In this study we have developed a useful method to identify a particular yeast strain within a mixture of strains during must fermentation, based on the presence or absence of a stable genetic element derived from Saccharomyces cerevisiae 23S RNA autonomous replicon. 23S RNA is a natural virus-like RNA replicon present in some S. cerevisiae strains, which encodes only its own RNA-dependent RNA polymerase named p104. A modified version of 23S RNA (23S-tagged RNA) was generated after transformation of S. cerevisiae wine strains with a launching plasmid, where six nucleotides were changed in the 23S RNA cDNA sequence without modifying the amino acid sequence of p104 RNA polymerase. Once generated, the 23S-tagged RNA can replicate autonomously (without the plasmid), is very stable, is present in high copy number in stationary phase or nitrogen-starved cells and confers no phenotype to the host, like the endogenous 23S RNA replicon. However, it can be distinguished from endogenous 23S RNA by reverse transcription followed by polymerase chain reaction (RT-PCR) with specific oligonucleotide primers. 23S RNA-derived replicon can be used to tag wine yeast strains in order to monitor easily their prevalence over endogenous strains during wine fermentation.

[Selection and implantation of yeast strains of genus Saccharomyces at a winery regulated by Appellation Contrôlée "Chacolí de Vizcaya/Bizkaiko Txakolina"]

The white wine Chacolía de Vizcaya/Bizkaiko Txakolina is characteristic from The Basque Country region and regulated under Appellation Contrôlée standards (BOPV 14/6/94). The objective of this study was the identification and selection of autochthonous yeast strains, to improve the conditions used to maintain the typical characteristics of this region wines. Yeasts identified as Saccharomyces bayanus isolated around these fields from 1996 to 1998, were subjected to a selective procedure based on enological characteristics and fermentative behaviour. Three of the selected strains were used to inoculate, at winery scale, two grape juice varieties accepted by the Appellation Contrôlée (Hondarrabi Zuri and Folle Blanche). The inoculated strains on the respective vinifications was followed by restriction fragment length polymorphism of mitochondrial DNA (REAmt) method with AluI enzyme, due to their specificity, short outcome, and technological simplicity compared with other molecular typing methods such as: chromosomal karyotyping analyzed by pulsed field gel electrophoresis, Random Amplified Polymorphic DNA-PCR (RAPD-PCR) and restriction fragment length polymorphism using the infrequently cutting enzyme SfiI (REA infrequent). This study demonstrated that strains with different phenotypic traits could show indistinguishable restriction patterns with REAmt, but could be discriminated using other typing methods such as RAPD-PCR, which although showing low reproducibility could be used as complementary to REAmt. Our results demonstrate that in spite of using autochthonous selected strains, the inoculation of musts with a particular strain do not guarantee its predominance and driving fermentation features. Of all yeast strains studied, strain no. 2 showed the best results in sensory testing and at the implantation process. Therefore, it could be used with commercial purposes for the production of Chacolí de Vizcaya/Bizkaiko Txakolina, especially when using musts from Folle Blanche.

Influence of grape treatment on the wine yeast populations isolated from spontaneous fermentations

AIM

To study the influence of different methods of grape treatment in wineries on the diversity of the yeast species in spontaneous fermentations.

METHODS AND RESULTS

Grapes were crushed and pressed in three different ways followed by spontaneous fermentation. The same grape material picked and crushed aseptically directly in the vineyard served as control. Yeasts isolated at different stages of the fermentation were characterized by 5.8S-ITS-RFLP. Yeasts of the Saccharomyces sensu stricto complex were additionally analysed by microsatellite polymerase chain reaction fingerprinting. The diversity of yeast species isolated from winery fermentations was much greater than from the vineyard fermentation in respect to yeasts of the genus Saccharomyces as well as non-Saccharomyces.

CONCLUSIONS

Oenonogical methods alter significantly the yeast diversity in spontaneous fermentations of grape juice.

SIGNIFICANCE AND IMPACT OF THE STUDY

Managing spontaneous fermentations successfully depends not only on choosing the suitable grapes but also on the crushing and pressing techniques leading to different yeast populations.

Selection of indigenous Saccharomyces cerevisiae strains according to their oenological characteristics and vinification results

Xynomavro and Muscat Hamburg grapes were fermented spontaneously, producing red and white wine, respectively. The indigenous yeast flora, isolated at three phases of these fermentations, was studied. One hundred and ten strains were isolated, eighty-four of which were identified as Saccharomyces cerevisiae. Six of these strains were selected for their satisfactory oenological properties to be tested as starters in wine fermentations. The quality of the produced wines was evaluated after determination of their aromatic compounds and sensory analysis. S. cerevisiae strain BT4, as well as the AM4+BM3 combination, were considered the best as they produced wines characterized by fruity aromas and were highly accepted among panelists.

Evidence for viable but nonculturable yeasts in botrytis-affected wine

AIMS

In Botrytis-affected wine, high concentrations of SO2 are added to stop the alcoholic fermentation and to stabilize the wine. During maturing in barrels or bottle-ageing, an unwanted refermentation can sometimes occur. However, results of the usual plate count of wine samples at the beginning of maturing suggest wine microbial stability. The aim of this study was to investigate the mode of yeasts survival after the addition of SO2 and to identify surviving yeasts.

METHODS AND RESULTS

Using direct epifluorescence technique, we observed the behaviour of cells after SO2 addition and compared the cell number determined by this method with the result of plate counts. The persistent yeast species were identified using two methods: polymerase chain reaction (PCR)-restriction fragment length polymorphism and PCR-denaturing gradient gel electrophoresis. They were identified as Saccharomyces cerevisiae and Candida stellata, and after few months of maturing, other spoiling yeasts appeared, like Rhodotorula mucilaginosa or Zygosaccharomyces bailii.

CONCLUSIONS

All characteristics of the cells lead to the conclusion that yeast persisted in wine in a viable but nonculturable-like state (VBNC). Suppression of the effect of free-SO2 did not lead to the resuscitation of the cells; however, another method proved the capacity of the cells to exit from the VBNC-like state.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study permits the characterization of the presence of VBNC-like yeasts in wine. The 'refermentation' phenomenon is probably due to the exit of the VBNC state.