Screening and characterization of indigenous yeast strains from spontaneously fermented strawberry (Fragaria × ananassa Duchesne) juice for potential wine production.

This study aimed to identify and characterize indigenous yeast strains suitable for the fermentation of Fragaria × ananassa Duchesne (strawberry) wine. A total of 58 yeast isolates were obtained from spontaneously fermented strawberry juice. Preliminary screening based on colony morphology on Wallerstein Laboratory (WL) nutrient agar yielded 15 candidate strains. Subsequent evaluation of CO₂ production using Durham tube fermentation assays further narrowed the selection to 12 high-performing isolates. Lysine utilization testing indicated that strain Z-36 belonged to Saccharomyces cerevisiae, whereas the remaining 11 isolates were classified as non-Saccharomyces yeasts. Comprehensive physiological tolerance profiling revealed distinct functional characteristics among the selected strains: strain Z-36 exhibited robust tolerance to multiple stress conditions, including cold stress at 4 °C, ethanol concentrations up to 15% (v/v), sucrose levels of 400 g/L, SO₂ concentrations of 360 mg/L, and low pH, rendering it especially well-suited for demanding fermentation environments; strain Z-1 demonstrated superior thermotolerance at 40 °C; strain Z-50 displayed exceptional resistance to high glucose concentration (400 g/L), strong resistance to common microbial inhibitors, and notably high ester biosynthetic capacity; and both strains Z-25 and Z-36 achieved outstanding ethanol yields. Molecular identification, based on sequencing of the D1/D2 domain of the large subunit rRNA gene, classified the 12 strains as follows: five Pichia fermentans, four Pichia kudriavzevii, two Hanseniaspora spp., and one S. cerevisiae. Integrating morphological, biochemical, physiological, and molecular data, strains Z-36 (S. cerevisiae) and Z-50 (Hanseniaspora sp.) were selected as optimal candidates for strawberry wine fermentation. However, we emphasize that these conclusions are drawn from in vitro screening assays; validation through actual strawberry wine fermentations with chemical and sensory analyses is required to confirm their technological suitability. This work provides a scientifically grounded foundation for the targeted development of starter cultures and informs future studies on strain optimization and mixed-fermentation strategies.