Abstract
In this investigation, we explored the oenological significance of Candida zemplinina (syn. Starmerella bacillaris) isolates from Apulian grape musts. Moreover, we provide the first evidence of the impact of different C. zemplinina strains on the wine aromatic properties tested as monocultures. We described the diversity of C. zemplinina strains isolated from grapes and the variability of ‘volatile’ phenotypes associated with this intraspecific variability. Thirty-three isolates were characterized at strain level by PCR-based approach and, among these, 16 strains were identified and then tested by microfermentation tests carried out in grape must. Analyzed strains were low producers of acetic acid and hydrogen sulphide, not able to decarboxylate a panel of representative amino acids, whereas they showed fructophilic character and significant glycerol production. Volatile profiles of produced wines were investigated by gas chromatography–mass spectrometry. The Odor Activity Values of all molecules were calculated and 12 compounds showed values above their odor thresholds. Two selected strains (35NC1 and 15PR1) could be considered as possible starter cultures since they were able to positively affect the sensory properties of obtained wine. This report firstly supplies evidence on the strain-specific impact of different C. zemplinina strains on the final aroma of produced wines.
Highlights
The transformation of grape juice into wine is a complex microbial reaction characterized by the sequential development of various species and strains of oenological yeasts
The analyzed population was composed of 33 C. zemplinina isolates (Table S1) selected from spontaneous feTrmheenatantaiolynzseodf Npeogpruolaamtioarno gwraaps ecmomusptoasneddfoorfme3r3lyCch. azreamctpelriinzienda aitstohleatsepsec(iTesablelveelS[12)0].seTloecatsesdessfrom spotnhteandeivoeurssifteyrwmietnhtinattihoinsspoofpNuleagtiroona,mthaerodigscrearpneinmg ucastpaacnidtyfoofrmthererelyPcChRa-rbaacsteedrizmeedthaot dths ewsepreeceiveasllueavteeld[20]
All the analyzed strains showed the same fermentation kinetics characterized by the start of the alcoholic fermentation process, 48 h after inoculation (Figure S6)
Summary
The transformation of grape juice into wine is a complex microbial reaction characterized by the sequential development of various species and strains of oenological yeasts. The spontaneous fermentation process is driven by indigenous microbes associated with grapes and the winery environment [1,2,3] Among these yeasts, the early stages of fermentation are characterized by progressive development of non-Saccharomyces yeasts, such as Candida spp., Hanseniaspora spp., Kluyveromyces spp., Pichia spp., and Rhodotorula spp., and subsequently, S. cerevisiae proliferates, dominating and completing the wine fermentation [4]. It was already shown that C. zemplinina strains may play relevant activities during winemaking, due to their remarkably fructophilic nature and low ethanol production rate [14,21] Strains belonging to this species, when inoculated at first, were able to alleviate the osmotic stress of S. cerevisiae cells by selectively consuming sugars [22]. The identified strains were tested as monocultures in microfermentation trials monitoring the chemical and volatile profiles during the fermentative process, allowing an investigation of the strain-specific influence of the selected strains on produced volatile compounds
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