Isolation, Screening and Characterization of Stress-tolerant Yeasts from Overripe Apple and Banana for Wine Production

Abstract

The search for robust, indigenous yeast strains is crucial for advancing local fermentation industries, particularly in tropical regions where high-temperature fermentations are common. This study aimed to isolate, screen, and characterize stress-tolerant yeasts from overripe apple and banana fruits for their potential application in wine production. Yeasts were isolated using enrichment culture technique on Yeast Extract Peptone Dextrose (YEPD) agar. Four distinct isolates (Y-01, Y-02, Y-03, Y-04) were selected and characterized based on their morphological and biochemical properties. Sugar fermentation profiles tentatively identified isolates Y-01 and Y-03 as Saccharomyces cerevisiae, while Y-02 and Y-04 were identified as Candida species. The isolates were evaluated for key oenological stress tolerances: thermotolerance (25 °C – 44 °C), ethanol tolerance (0% - 14% v/v), and acid tolerance (pH 2 - 10). The results revealed significant variation among the isolates. Isolate Y-03 demonstrated superior stress tolerance, exhibiting robust growth at 40 °C, sustaining growth in up to 12% (v/v) ethanol, and maintaining good growth across a wide pH range (2-8) with an optimum at pH 4-6. The study thus revealed that overripe fruits could serve as valuable reservoir for indigenous yeasts. Isolate Y-03, identified as a strain of Saccharomyces cerevisiae, emerged as a highly promising candidate for fruit wine production due to its exceptional multi-stress tolerance, which is essential for dominating fermentation and ensuring process efficiency under the variable conditions typical of local production settings.