Yeasts and yeast-like fungal isolates were recovered from apple orchards and apple juice processing plants located in the Shaanxi province of China. The strains were evaluated for osmotolerance by growing them in 50% (w/v) glucose. Of the strains tested, 66 were positive for osmotolerance and were subsequently identified by 26S or 5.8S-ITS ribosomal RNA (rRNA) gene sequencing. Physiological tests and RAPD-PCR analysis were performed to reveal the polymorphism of isolates belonging to the same species. Further, the spoilage potential of the 66 isolates was determining by evaluating their growth in 50% to 70% (w/v) glucose and measuring gas generation in 50% (w/v) glucose. Thirteen osmotolerant isolates representing 9 species were obtained from 10 apple orchards and 53 target isolates representing 19 species were recovered from 2 apple juice processing plants. In total, members of 14 genera and 23 species of osmotolerant isolates including yeast-like molds were recovered from all sources. The commonly recovered osmotolerant isolates belonged to Kluyveromyces marxianus, Hanseniaspora uvarum, Saccharomyces cerevisiae, Zygosaccharomyces rouxii, Candida tropicalis, and Pichia kudriavzevii. The polymorphism of isolates belonging to the same species was limited to 1 to 3 biotypes. The majority of species were capable of growing within a range of glucose concentration, similar to sugar concentrations found in apple juice products with a lag phase from 96 to 192 h. Overall, Z. rouxii was particularly the most tolerant to high glucose concentration with the shortest lag phase of 48 h in 70% (w/v) glucose and the fastest gas generation rate in 50% (w/v) glucose.
Keywords: apple juice processing plants; apple orchards; food spoilage; osmotolerant yeasts; yeast-like molds.
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