Isolation and Biochemical Characterization of Yeast Strains from Fruits

Abstract

The present study focused on the isolation and biochemical characterization of yeast strains from  fruits to evaluate their metabolic and functional diversity. Yeasts were isolated from fresh fruit samples such as grape, orange, pineapple, lychee, sugarcane juice, using Yeast Glucose Agar supplemented with chloramphenicol. Five yeast isolates (YS1–YS5) were obtained and highest count of 2.56 log10 CFU/mL in sugarcane juice. Morphological characterization using lactophenol cotton blue staining revealed oval to round yeast cells with budding and occasional ascospores. Biochemical characterization demonstrated considerable variability among the isolates. Sugar fermentation tests showed positive fermentation for YS2, YS3 and YS4. Nitrogen utilization studies indicated that all isolates could utilize ethylamine and tryptophan, while only YS5 was able to utilize DL-lysine. Complementary tests revealed that most isolates tolerated 5–10% NaCl (YS1-YS5) and 1% acetic acid (except YS 1), with several strains showing delayed but measurable growth even at 16% NaCl, indicating strong stress tolerance. Urease activity was not detected in any isolates. Oxidation–fermentation tests showed predominantly oxidative metabolism, Overall, the results highlight significant physiological and metabolic diversity among yeast isolates from food sources, suggesting their potential applicability in fermentation processes and functional food development.