Yeasts, associated with secondary flora of many cheese types, are important microorganisms for cheese ripening process. The aim of this study was to identify the yeasts isolated from traditional Mihalic cheese and to determine their enzymatic activities as a tool for their technological characteristics. Phenotypic identification was performed by using API ID 32C test system and some complementary morphological, physiological and biochemical tests. Enzyme profiles of the isolates were determined by using API-ZYM strips. In this study, 72 yeast isolates were obtained from 29 Mihalic cheese samples. Fifty-six (78%) of the isolates could be identified at species level, and one isolate at genus level. The identified yeast species belonged to three genera; Candida, Geotrichum and Trichosporon. It was determined that Candida famata var. famata was the dominant species in Mihalic cheese. The yeast isolates had variable enzyme activities including acid phosphatase, esterase, esterase lipase, lipase, β-galactosidase, leucine arylamidase, valine arylamidase and cysteine arylamidase, which could have important attributes during cheese ripening. C. famata var. famata M22, Candida guilliermondii var. membranefaciens M54 and Candida tropicalis M2 were selected to be superior strains on the basis of their enzyme profiles. Identification and enzymatic characterization of the yeasts originated from Mihalic cheese was performed for the first time in this study.

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Some lignocellulosic food byproducts such as potato peels, wheat bran, barley bran and chestnut shells were evaluated as potential sources of xylose for microbial xylitol production by yeasts. Potential yeast strains were selected after screening xylitol production of some indigenous yeasts in a defined fermentation medium. Candida tropicalis strains gave the highest results with 83.28 and 54.07 g/L xylitol production from 100 g/L xylose. Lignocellulosic materials were exposed to acid hydrolysis at different conditions. Chestnut shells gave the highest xylose yield and the hydrolysate of chestnut shells was used in further experiments in which xylitol productions of two potential C. tropicalis strains were investigated. Combined detoxification method including evaporation, overliming and activated charcoal with the use of threefold concentration and also yeast extract supplementation suggested to be efficient for both growth and product formation in chestnut shell hydrolysate in which 40 % xylitol yield was obtained. It was concluded that detoxified and fortified chestnut shell hydrolysate could be a potential medium for xylitol production.

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