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Brazilian Journal of Microbiology

Print version ISSN 1517-8382On-line version ISSN 1678-4405

Braz. J. Microbiol. vol.47 no.1 São Paulo Jan./Mar. 2016

http://dx.doi.org/10.1016/j.bjm.2015.11.010 

Food Microbiology

Isolation, identification and characterization of regional indigenous Saccharomyces cerevisiae strains

Hana Šuranská*  1 

Dana Vránová1 

Jiřina Omelková1 

1Brno University of Technology, Faculty of Chemistry, Department of Food Science and Biotechnology, Purkyňova 464/118, 612 00 Brno, Czech Republic

Abstract

In the present work we isolated and identified various indigenous Saccharomyces cerevisiae strains and screened them for the selected oenological properties. These S. cerevisiae strains were isolated from berries and spontaneously fermented musts. The grape berries (Sauvignon blanc and Pinot noir) were grown under the integrated and organic mode of farming in the South Moravia (Czech Republic) wine region. Modern genotyping techniques such as PCR-fingerprinting and interdelta PCR typing were employed to differentiate among indigenous S. cerevisiae strains. This combination of the methods provides a rapid and relatively simple approach for identification of yeast of S. cerevisiae at strain level. In total, 120 isolates were identified and grouped by molecular approaches and 45 of the representative strains were tested for selected important oenological properties including ethanol, sulfur dioxide and osmotic stress tolerance, intensity of flocculation and desirable enzymatic activities. Their ability to produce and utilize acetic/malic acid was examined as well; in addition, H2S production as an undesirable property was screened. The oenological characteristics of indigenous isolates were compared to a commercially available S. cerevisiae BS6 strain, which is commonly used as the starter culture. Finally, some indigenous strains coming from organically treated grape berries were chosen for their promising oenological properties and these strains will be used as the starter culture, because application of a selected indigenous S. cerevisiae strain can enhance the regional character of the wines.

Keywords Saccharomyces genus; Oenological properties; ITS-PCR-RFLP; Interdelta PCR typing; Species-specific primers

Introduction

The quality of fermented foods and beverages is partially determined by the microorganisms used for their production. For instance, the secondary character of wine is determined by sensory characteristics that arise from the direct action of microorganisms on the substrate. The fermentation of grape must into wine is an ecologically complex process, in which bacteria and other microorganisms, especially yeasts, play a crucial role. The strains of Saccharomyces cerevisiae involved in fermentation play an important part in the characteristics of the final product and the diversity of S. cerevisiae strains present in spontaneous fermentation contribute to the chemical composition and sensory qualities of the resulting wine.1

Therefore, one of the most important technological advances in wine-making was the inoculation of grape juice with selected cultures of S. cerevisiae.2 This approach is based on the evidence that microbiological control of the fermentation process allows better management of this alcoholic fermentation. It is known that selected strains of S. cerevisiae suppress indigenous non-Saccharomyces species and dominate the fermentation process.35

Nowadays, novel biotechnological approaches in winemaking are used in several aspects of the fermentation industry. Apart from the monitoring of the microbial populations and the control of the spoilage yeasts, attention is focused also on the selection and utilization of the starter cultures coming from one's own vineyard, which can enhance the regional character of the wine.6,7 The metabolic peculiarities and the physiological properties of S. cerevisiae yeast may lead to the formation of metabolites and the transformation of grape substances that may enrich the wine flavor.7 Certain criteria need to be met in order to guarantee the desirable features of the yeast strains selected. The most important ones are: tolerance to ethanol; growth at high sugar concentrations; resistance to sulfur dioxide; low production of hydrogen sulfide; production of killer toxins or some enzymatic activities.8

Furthermore, only reliable and rapid identification of the yeast species during the process and the quality control enables enologists to assess the role of yeasts as a main protagonist of alcoholic fermentation or as a contaminant. The utilization of molecular methods enabled rapid and precise identification of the yeasts at the species or strain level.1 Mercado et al.9 reported that Saccharomyces populations are represented by multiple strains, even in inoculated fermentations. Therefore, it is important to have simple and appropriate methods that allow discrimination at the strain level.

This study is focused on indigenous S. cerevisiae strain (i) selection, (ii) identification and (iii) technological characterization. Yeasts were isolated from grapes and musts during the production of wines. We selected two types of wine varieties – Sauvignon blanc and Pinot noir coming from an organic and integrated treated vineyard situated in South Moravia, Czech Republic. Our objective was also focused on the selection of the identification approaches that will be simple and suitable for rapid and reliable strain identification. Therefore, isolates of S. cerevisiae were identified and grouped by several molecular approaches such as ITS-PCR-RFLP, PCR-fingerprinting, species-specific primers and interdelta PCR typing. The combination of these techniques enabled rapid detection, identification and typing of different S. cerevisiae strains. Finally, the isolated strains were screened for selected technological properties important in the winemaking process and for further application as the starter cultures. To sum up, this study has demonstrated the importance of selection of an appropriate and rapid identification technique and also determination of some important oenological properties.

Methods

Yeast species isolation and cultivation

Autochthonous (indigenous) strains belonging to Saccharomyces genus were isolated from grape berries and also from spontaneously fermented musts in different stages of the fermentation process.

Grapes were collected at the Ivaň vineyard situated in the South Moravia region and belong to the Mikulov wine region, Czech Republic. Red wine Pinot Noir (Pn) and white wine Sauvignon blanc (Sg) cultivars of Vitis vinifera were chosen. Both varieties, typical cultivars for white and, respectively, red Moravian wine production, were cultivated using the organic (O) and also integrated (I) farming procedure. Grape berries (healthy and undamaged) were collected before harvest (in September 2009, 2010, 2011) into sterile glasses. Immediately after transportation to the laboratory, 15–20 grape berries were placed into 150 mL of Malt extract medium MEM (Himedia; 2% malt extract, 0.1% peptone, 2% dextrose, 2% agar) and cultivated for 10 days at laboratory temperature (approx. 23 °C). After that, culture media (300 µL) inoculated onto MEM agar plates supplemented with 250 mg L−1 streptomycin sulfate (Himedia, India) were incubated at 26 °C for 3–5 days. The single colonies were obtained by Koch's dilution method.

The fermentation process was performed in the cellar in Ivaň (during the vintage 2009, 2010, 2011), which was separated from common fermentations of commercial wine production. The fermentation process following the standard procedure was conducted in a 1000 L barrel. The cellar temperature was approx. 10 °C and the temperature of the fermentation was approx. 18 °C. The must was spontaneously fermented and the samples were collected 3 times per week during the whole fermentation process.

Yeast populations from must were isolated as described previously10 and cultivated on malt extract medium (MEM) supplemented with 250 mg L−1 streptomycin sulfate (Himedia, India). The single colonies (pure culture) were obtained by Koch's dilution method.

In total, 120 Saccharomyces sp. strains were isolated and identified. Pure cultures were preserved on MEM agar under paraffin oil. The most promising strains will be deposited in the yeast culture collection CCY Bratislava (strain S. cerevisiae 1-09 has already been deposited there).

DNA isolation

Genomic DNA was isolated from single colonies using the commercial kit UltraClean ™ Microbial DNA Isolation Kit (MoBio, USA) according to the manufacturer's protocol.

ITS-PCR-RFLP

To distinguish Saccharomyces sp. from other isolates, ITS-PCR-RFLP was employed. The internal transcribed spacers (ITS) (ITS1 and ITS2) and 5.8S rDNA gene regions were amplified by using specific primers ITS1 (5'-TCCGTAGGTGAACCTGCGG-3') and ITS4 (5'-TCCTCCGCTTATTGATATGC-3').11 DNA amplification was carried out in the final volume of 50 µL containing 0.2 mM of dNTP, 0.5 µL of each primer 100 pmol µL−1, 1 × PCR reaction buffer and 1 U of Taq DNA polymerase (Kapa Biosystems, USA). PCR conditions were as follows: initial denaturation cycle at 94 °C for 4 min followed by 25 cycles of amplification, denaturation at 94 °C for 1 min, annealing at 48 °C for 30 s, and extension at 72 °C for 1 min; final extension at 72 °C for 10 min.

For RFLP, PCR products were purified by ethanol precipitation and digested by restriction endonucleases HaeIII (Fermentas, USA) following the manufacturer's instructions.

Species-specific primers

For S. cerevisiae species identification, a set of pairs of species-specific primers ScerF2 (5'-GCGCTTTACATTCAGATCCCGAG-3') and ScerR2 (5'-TAAGTTGGTTGTCAGCAAGATTG-3') were used.12 DNA amplification was carried out in a final volume of 25 µL containing 0.2 mM of dNTP (Invitek, Germany), 0.5 µL of each primer 100 pmol µL−1 (GeneriBiotech, Czech Republic), 1 × PCR reaction buffer, 1.5 mM MgCl2 and 1.25 U Taq DNA polymerase (BioRad, USA) and 0.5 µL of template DNA. PCR cycling conditions used were: initial denaturation cycle at 94 °C for 4 min followed by 30 cycles of amplification, denaturation at 94 °C for 1 min, annealing at 55 °C for 1 min, and extension at 72 °C for 1 min; final extension at 72 °C for 2 min.

PCR-fingerprinting and interdelta PCR typing

In order to distinguish different S. cerevisiae strains, PCR-fingerprinting by using M13 primer and interdelta primers were used. DNA amplification was carried out in a final volume of 25 µL containing 0.2 mM of dNTP (Invitek, Germany), 0.5 µL of each primer 100 pmol µL−1 (VBC Biotech, Germany), 1 × PCR reaction buffer and 1 U Taq DNA polymerase (Kapa, USA) and 0.5 µL of template DNA.

PCR-assays by using M13 primer (5'-GAGGGTGGCGGTTCT-3'):13 initial denaturation cycle at 95 °C for 5 min, followed by 40 cycles of amplification followed by denaturation at 93 °C for 0.75 s, annealing at 50 °C for 1 min, and extension at 72 °C for 1 min; final extension at 72 °C for 6 min. The second PCR-assay for M13 primer: initial denaturation cycle at 94 °C for 4 min, followed by 35 cycles of amplification followed by denaturation at 94 °C for 30 s, annealing at 36 °C for 45 s, and extension at 72 °C for 45 s; final extension at 72 °C for 7 min.

The conditions for interdelta PCR typing by δ1 (5'-CAAAATTCACCTATATTCTCA-3') and δ2 (5'-GTGGATTTTTATTCCAACA-3'); δ2 (5'-GTGGATTTTTATTCCAACA-3') and δ12 (5'-TCAACAATGGAATCCCAAC-3')14,15 were as follows: initial denaturation cycle at 94 °C for 4 min, followed by 30 cycles of amplification–denaturation at 94 °C for 30 s, annealing at 49 °C for 1 min and extension at 72 °C for 2 min. The final extension was at 72 °C for 10 min.

Detection of PCR products

PCR products and restriction fragments were separated and detected by electrophoresis on 2% (w/v) agarose gel in 1 × TBE buffer at 5 V cm−1 for 2 h. DNA amplified by single repetitive primers and by delta primers were separated on 1.5% agarose gel for 3–4 h. The gels were stained by ethidium bromide (10 mg L−1), visualized under UV light (Ultra Lum. Inc., USA) and documented by ScionImage software (Scion, India). Finally, electrophoreograms were processed by the BioNumerics 6.5 software employing UPGMA cluster analysis.

Screening of oenological properties

Flocculation properties of selected strains were tested according to Bony et al.16 with slight modification. Yeasts were cultured for 3 days at 26 °C in tubes containing 10 mL of YPD (2% peptone, 1% yeast extract and 2% glucose) medium under permanent shaking (150 rpm). Cells were collected by centrifugation and washed with deionized water. After that, cells were suspended into 10 mL of 50 mM acetate buffer (pH 4.5) enriched by 3 mM CaSO4. The tubes of suspended cells were mixed for 30 s and the turbidity of yeast suspension was evaluated by the naked eye. Flocculation degree was determined using a subjective scale which means that the sedimentation was observed depending on the time. The following evaluation was used: + the cells flocculate and sediment after 15 min (partially clear solution); ++ immediate flocculation; w – flocculation after 1 h.

Ethanol tolerance was tested in 5 mL of YPD medium supplemented by 12, 14, 15, 16 and 17% (v/v) ethanol and the tubes were inoculated by 100 µL of cell suspension (cell concentration approx. 5 log CFU mL−1). Inoculated tubes were cultivated at 26 °C for 10 days. The culture density was measured daily by DEN-1B densitometer (Biosan, Latvia). Specific growth rate µ (h−1) and the length of the lag phase t (h) were estimated.

Osmotolerance of selected strains was tested in 5 mL of YPD medium with 40% (w/v) and 50% (w/v) glucose. The cells density was measured as described above.

H2S production by selected strains was tested on Biggy agar (Himedia, India) which contains bismuth as an indicator. After incubation at 26 °C for 3–5 days, the zone surrounding the colony was evaluated as the follows: − no production; + white colonies; ++ light brown; +++ brown; ++++ dark brown/black.5

Malic and acetic acid utilization by selected strains was tested on 0.67% yeast nitrogen base (YNB, Himedia) agar plates containing 0.5% (w/v) malic acid, respectively, 0.25% (w/v) acetic acid. The growth of colonies was screened. Acetic acid production was screened on CaCO3 agar plates (Custer's chalk medium) containing 0.5% yeast extract, 5% glucose, 0.5% CaCO3 and 2% agar. The acetic acid production enabled solubility of CaCO3 which resulted as a clear zone surrounding the colonies.5

The isolated yeasts were also tested for some enzymatic activities such as β-glucosidase and glycosidase activities. The activities were determined by agar plating. The plates were incubated at 26 °C for 3–5 days.17

β-Glucosidase activity was screened onto selective medium containing 0.67% yeast nitrogen base (YNB, Himedia), 0.5% arbutin and 2% agar. The pH of the medium was adjusted to 5 before autoclaving. Two milliliters of a filter sterilized 1% ferric ammonium citrate solution was added to 100 mL media before plates pouring. Colonies showing activity were identified by a dark brown halo around the colonies.17

Glycosidase activity was determined using the plates with the selective medium containing 0.67% yeast nitrogen base (YNB, Himedia), 0.2% rutin and 2% agar. The glycosidase activity was detected as a clear zone around the colonies.5,17

Results and discussion

Selection and identification of S. cerevisiae strains

In total, we isolated 120 single colonies of autochthonous Saccharomyces sp. strains from 524 total yeasts. Yeasts were isolated from Sauvignon blanc (Sg) and Pinot noir (Pn) coming from organic (O) and integrated (I) farming. The yeast species were isolated from grape berries as well as from spontaneously fermented must during the vintage 2009 (09), 2010 (10) and 2011 (11). The list of the Saccharomyces isolates and the sources of their isolation are shown in Table 1.

Table 1 Number of Saccharomyces sp. isolates. 

Grape variety Vintage Number of Saccharomyces sp. isolates
Integrated (I) Organic (O)
Grapes (B)/must (M) Grapes (B)/must (M)
Sauvignon blanc (Sg) 2009 1/14 1/11
Pinot noir (Pn) 2010 0/14 0/17
Sauvignon blanc (Sg) 2011 0/20 0/17
Pinot noir (Pn) 2011 1/14 0/10
Total 120
Total of yeasts isolates 524

Yeasts of the genus Saccharomyces were distinguished from the other isolates (from non-Saccharomyces species) by ITS-PCR-RFLP (the length of PCR amplicon was 880 bp). Further, for S. cerevisiae species identification we employed species-specific primers ScerF2 and ScerR2.12 Species-specific primers enable us to identify and distinguish S. cerevisiae species from other species belonging to the Saccharomyces sensu stricto complex, which includes the species which can also be found in fermented must (for. ex. Saccharomyces bayanus, Saccharomyces pastorianus, Saccharomyces kudriavzevii). Based on our results, all the isolates belonging to the Saccharomyces genus were identified by species-specific primers as S. cerevisiae (the length of the PCR products was 150 bp) (data not shown).

Further, two different PCR-assays by using M13 primer were used. These assays differed in annealing temperature (50 °C vs. 36 °C). The isolates were divided into three groups by the first assay with annealing temperature 50 °C and into four groups by the second PCR-assay (36 °C). Data are presented as part of the dendrogram (Fig. 1). Two isolates (marked as U, T) exhibited a different fingerprinting profile than the rest of the isolates; these isolates may be hybrids of S. cerevisiae and another species belonging to the Saccharomyces genus. Hence, PCR-fingerprinting techniques using M13 primer are able to group the species members of Saccharomyces genus but they are not suitable for resolving.

Fig. 1 Dendrogram based on the similarity of PCR-fingerprinting patterns of S. cerevisiae isolates. S. cerevisiae BS6 – control strain. The description on the right side of the dendrogram is the label of the isolated S. cerevisiae strains. 

In order to distinguish various S. cerevisiae strains, we employed δ1– δ2 and δ12– δ2 primers amplifying inter-delta sequences. These delta elements are described as appropriate genetic markers for identification of polymorphisms because the number and location have a certain intraspecific variability.18 The primer pair δ1– δ2 generated from three to eight different fragments per strain with one common band of the size of approximately 1000 bp. On the other hand, primer pair δ12– δ2 provided significantly more fragments per sample and some of them were of low intensity. The low number of fragments per sample is ascribed to the weak homology exhibited by the primer δ1– δ2 towards the whole sequence of S. cerevisiae genom.19 However, by combination of these two sets of delta primers, we identified 45 different S. cerevisiae strains. The majority of the isolated and identified S. cerevisiae strains came from spontaneous fermented musts and belonged to group A (strain A). Despite the fact that some authors20,21 reported that it is almost impossible to isolate Saccharomyces sp. populations from berries and initial must by standard direct agar plating procedure due to their low counts (>10–100 CFU cm−2) we isolated three strains from grape berries (see Table 1). The electrophoretic patterns and final dendrogram showing the genetics similarity of various identified S. cerevisiae strains are shown in Fig. 1.

The novel combination of the modern molecular approaches used in this study for strain identification and typing seems to be suitable for rapid, reliable, simple and reproducible identification of S. cerevisiae strains. Schuller et al.,22 Maqueda et al.23 or Ortiz et al.24 reported application of mitochondrial DNA restriction analysis or karyotyping in order to distinguish various strains of S. cerevisiae. However, these methods are labor intensive and the results are influenced by complexity of data interpretation due to the high number of generated fragments after mtDNA RFLP. On the contrary, we employed different approaches to the group and distinguish Saccharomyces at strain level based on consequent employment of PCR-fingerprinting. For instance Schuller et al.22 reported that interdelta PCR typing had very similar resolving power at strain level as mtDNA and karyotyping, therefore, the unique combination of the methods utilized in this work can be considered as a simple and rapid alternative to mtDNA or karyotyping.

Screening of selected oenological properties of various S. cerevisiae strains

Because not all yeast strains are relevant for the specific conditions and characteristics of wine, a number of criteria have been proposed for the selection of new yeast strains for use in the winemaking process. One of the most important criterions for high-quality wine production is use of S. cerevisiae strain with suitable technological properties. Thus, in order to investigate phenotypic differences among 45 indigenous S. cerevisiae strains, which were identified by molecular method as different strains (see above), we screened them for the selected technological properties. The strain S. cerevisiae BS6, which is commercially available, was used as a control strain. The complete list of results, summarizing oenological properties that are important for strain selection and their application in the winemaking process, is provided in Table 2. The use of local, autochthonous, selected strains of S. cerevisiae as starters is rather preferable, since these yeasts are better acclimated to particular conditions characteristics for the specific region/area of wine production8 and, moreover, utilization of the local isolate of S. cerevisiae is likely to raise the regional character of the wine.

Table 2 Oenological properties of different indigenous Saccharomyces cerevisiae strains and one commercial S. cerevisiae strain BS6 as a control. Pn – Pinot Noir; O, I – organic, integrated; M, B – must, grape berries; 09–11 – mean year of isolation (2009–2011). The gray labelled fields – the strains which physiological properties were better than control strain BS6. 

Isolated strain Source of isolation Desirable technological properties Undesirable properties
Ethanol resistance (%) Osmotolerance H2S production
12% ethanol 14% ethanol Ethanol (%) 40% glucose 50% glucose SO2 tolerance MA utilization AA utilization AA production Glycosidase activity Flocculation
µ (h−1) b lag phase t (h) µ (h−1) b lag phase t (h) 15 16 17 µ (h−1) b lag phase t (h) µ (h−1) b lag phase t (h) 0.5% 0.25%
A PnIB-11 0.061 22 0.019 58 + 0.037 19 0.029 24 + + + w + ++
A1 SgOM-11 0.054 22 0.044 19 0.029 24 + + + w + ++
A2 PnOM-11 0.058 24 0.025 59 + 0.049 19 0.021 24 + + + + + +++
A3 PnIM-11 0.055 24 0.037 28 0.013 24 + + + + + ++
A4 SgIM-11 0.092 24 0.017 39 0.052 19 0.022 24 + + + + + ++
B PnOM-10 0.060 24 0.028 85 0.055 19 0.023 30 + w w w ++++
C SgOM-09 0.060 24 0.033 58 0.057 19 0.020 24 + w + + + +++
D PnOM-10 0.075 24 0.018 42 0.054 19 0.014 24 + + + w + +++
E PnIM-10 0.080 22 0.013 42 0.051 19 0.020 43 + + + w + ++++
E1 SgOM-11 0.057 24 0.033 80 0.051 19 0.020 24 + + + + + ++++
F SgOM-09 0.097 24 0.019 42 0.059 19 0.021 35 + + + + + +
F1 SgIM-11 0.073 16 0.017 43 0.051 19 0.020 24 + + + w + ++
G PnOM-10 0.058 24 0.018 45 0.065 19 0.021 28 + + + w + ++++
H SgIM-09 0.056 22 0.014 42 + 0.064 19 0.025 67 + + + + w ++++
I SgOM-09 0.090 22 0.063 24 0.052 19 0.019 51 + + + ++ + ++
J PnOM-10 0.055 24 0.046 24 0.058 19 0.024 52 + + + ++ + ++
K PnIM-10 0.061 14 0.034 68 0.060 19 0.016 43 + w + ++ + ++
K1 PnIM-11 0.065 24 0.032 68 0.060 24 0.022 45 + w + w + ++
L SgIB-09 0.071 22 0.018 40 0.071 19 0.019 43 + + + w + ++
M PnOM-10 0.061 14 0.017 40 + w 0.051 19 0.023 51 + + + ++ + +
N PnIM-10 0.068 20 0.023 58 0.055 19 0.022 45 + + + w + ++++
O PnIM-10 0.055 20 0.005 150 0.061 19 0.028 67 + + + w + ++++
P PnOM-10 0.080 24 0.028 50 0.068 24 0.020 51 + + + w + +
Q SgOM-09 0.078 24 0.014 42 0.061 19 0.012 43 + + + + +
R SgIM-09 0.060 24 0.013 24 0.062 19 0.018 43 + + + w + +
S SgIM-09 0.063 24 0.011 25 + 0.064 19 0.017 43 + + + + + +
T SgIM-09 0.070 24 0.010 24 + w 0.065 19 0.017 43 + + + + ++
U SgIM-09 0.062 22 0.013 42 0.057 24 0.020 35 + + + + ++
V SgOM-11 0.049 4 0.010 38 0.064 19 0.022 51 + + + + ++
W SgIM-11 0.060 20 0.013 24 + + 0.062 19 0.020 43 + + + + +
W1 PnIM-11 0.076 14 0.016 38 0.077 19 0.020 43 + + + + ++++
X SgIM-11 0.064 24 0.018 42 0.072 19 0.022 43 + + + + +
X1 PnOM-11 0.075 25 0.016 25 + + 0.064 19 0.018 51 + + + w + +
Y SgOM-11 0.073 22 0.006 24 0.065 19 0.022 67 + + + w + +
Z PnOM-11 0.064 16 0.007 24 0.058 19 0.018 43 + + + + + +
1-09 SgOB-09 0.067 22 0.009 24 + + 0.071 19 0.021 52 + + + w + +
2-09 SgIM-09 0.058 24 0.011 40 + + 0.064 19 0.016 55 + + + w + +
5-09 SgIM-09 0.062 22 0.010 42 0.065 19 0.024 46 + + + + ++++
13-09 SgOM-09 0.058 16 0.008 24 0.063 19 0.021 51 + + + w ++
15-09 SgOM-09 0.067 22 0.013 24 0.069 24 0.020 46 + + + + ++++
20-09 SgOM-09 0.059 22 0.006 26 + w 0.062 19 0.019 46 + + + + +
13-10 PnOM-10 0.062 20 0.009 40 0.060 19 0.020 60 + + + w +++
27-10 PnIM-10 0.065 24 0.003 80 0.065 19 0.021 44 + + + + ++
25-10 PnIM-10 0.063 20 0.014 42 0.060 19 0.020 26 + + + + ++
BS6 Control 0.064 20 0.012 24 0.070 24 0.018 26 + + + + ++
Positive (%) 100 96 24 9 100 100 91 98 29 91/2 9 a /20
Weak (%) 4 7 9 2 38 7 31/38
Negative (%) 76 84 100 0 33 100 2

aStrong positive; for H2S production: positive (+++ and ++++), weak (+ and ++).

bSpecific growth rate; the standard deviations were not higher than 20%.

Note : no glucosidase and glycosidase activities for all tested indigenous strains and also for commercial BS6 strain.

Barrajón et al.25 reported that high fermentation power is obviously related to the capacity of the strain to overcome the stress associated with wine fermentation. For this purpose, we tested osmotic and ethanol stress tolerance.

The major target of ethanol is the membrane, altering the membrane organization and permeability and consequently inhibiting glucose transport and fermentation rate under enological conditions.26 As expected, the physiological differences among the stress tolerant species S. cerevisiae depended on the strain. The growth parameters of all the tested strains including specific growth rate and length of the lag phase are listed in Table 2. Eighteen isolated strains revealed better growth characteristics than control strain BS6 in the presence of 12% ethanol and 29 showed higher growth rate when exposed to 14% ethanol. Further, four isolated strains (W, X1, 2-09, 1-09) were able to grow in 16% ethanol but none of the tested strains was able to grow in the presence of 17% ethanol.

Higher sugar content of the grape must can result in inhibition of the yeast metabolism and, therefore, in sluggish fermentation.24 Therefore, tolerance towards osmotic pressure is a desirable property of the yeast starter culture. All the isolated strains were capable of growing in the presence of 40% and 50% glucose. Four strains (W1, X, L and 1-09) exhibited higher growth rate than the control strain BS6 in the presence of 40% glucose. Interestingly, despite the fact that Tofalo et al.26 did not notice any growth of S. cerevisiae strains in the presence of 50% glucose, most of our isolates were capable of growing when cultivated in the presence of 50% glucose. Moreover, the majority of the screened strains revealed a higher growth rate on 50% glucose than the control strain.

Results of flocculation tests showed that, as also reported in other studies,24,27 most of the strains (91%) remained in suspension after 10 min at rest. This is an important feature when selecting active dried yeasts for vinification, where yeast should ideally remain in suspension during fermentation.24

Enzymes play a definitive role in the production of wine. The enzymatic activities do not only originate from the grapes itself, but also from yeasts and other microorganisms.17 Based on our results, tested strains lacked β-glucosidase activity. Unlike the other authors,5,28 we did not detect any glycosidase production by S. cerevisiae strains tested.

To produce a high-quality wine, it is important to obtain a fine balance between the various chemical constituents, especially between the sugar and acid content.29 As reported by Suárez-Lepe and Morata,7 yeasts might be selected for their ability to produce and degrade acetic and malic acid. Our results showed that 91% (98%) of our isolates were able to grow on the agar medium containing malic or acetic acid as sole carbon sources. The capability of degradation of malic as well as acetic acid may be considered as a desirable property of yeast strains because it leads to the deacidification of wine.30 On the contrary, acetic acid production was observed for 29% of tested strains. Several studies have linked the production of acetic acid to increased glycerol production which gives the wine a desirable property.31,32

Hydrogen sulfite has negative organoleptic impact on wine due to formation of off-flavors.7 Fifteen isolates (29%) synthesized H2S and remaining strains exhibited only low H2S production. Only one strain (B) did not produce H2S, however, this strain is not suitable for application as a starter culture due to strong flocculation properties.

Yeast selection offers the best way to obtain strains of S. cerevisiae or other oenological species with properties that might improve the sensorial profile, technological properties or regional character of the wine.7 The assays to determine yeast properties that could influence fermentative capacity and the ability to adapt to stressful conditions related to the wine-production process revealed differences for some strains. Some indigenous strains exhibited better adaption to stressful conditions than the control strain. On the contrary, some of them produced a high amount of hydrogen sulfite, causing off-flavor.

Thus, if we compare all the tested strains, only 15 (A, A4, F, F1, I, J, L, M, R, S, X1, Z, 1-09, 2-09, 27-10) of them are suitable for further testing as starter cultures. Based on our results, these strains showed proper technological properties that are very similar to the control commercial S. cerevisiae BS6 strain. These strains can be chosen for future large-scale fermentation processes instead of commercially available strains.

Conclusions

The present study demonstrated application of appropriate modern molecular techniques that are suitable for rapid S. cerevisiae strain identification and further testing of various strains for their technological potential. The combination of used modern molecular techniques including species-specific primers, and interdelta PCR typing enabled us to identify S. cerevisiae at strain level. Also important physiological characteristics of the yeasts used in this study are suitable for rapid selection of the different S. cerevisiae strains that can be applied in the winemaking process. Application of the selected strains with suitable technological properties in the wine fermentation process should increase the quality of the wine and enhance the regional character of traditional Moravian wines. Hence, some isolated indigenous strains will be tested in a large-scale fermentation process by a small Moravian winery.

Associate Editor: Maricê Nogueira de Oliveira

Acknowledgments

This work was supported by a project of MŠMT ČR (Grant No. MSM 0021630501) and by a Standard project of specific research No. FCH-S-13-1912.

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Received: July 29, 2014; Accepted: May 19, 2015

*Corresponding author. E-mail: suranska.h@gmail.com (H. Šuranská).

Conflicts of interest

The authors declare no conflicts of interest.

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