Oxygen requirements of the food spoilage yeast Zygosaccharomyces bailii insynthetic and complex media

Most yeast species can ferment sugars to ethanol, but only a few can grow i n the complete absence of oxygen. Oxygen availability might, therefore, be a key parameter in spoilage of food caused by fermentative yeasts, In this study, the oxygen requirement and regulation of alcoholic fermentation were studied in batch cultures of the spoilage yeast Zygosaccharomyces bailii a t a constant pH, pH 3.0, In aerobic, glucose-grown cultures, Z. bailii exhi bited aerobic alcoholic fermentation similar to that of Saccharomyces cerev isiae and other Crabtree-positive yeasts, In anaerobic fermenter cultures g rown on a synthetic medium supplemented with glucose, Tween 80, and ergoste rol, S. cerevisiae exhibited rapid exponential growth, Growth of Z, bailii under these conditions was extremely slow and linear. These linear growth k inetics indicate that cell proliferation of Z. bailii in the anaerobic ferm enters was limited by a constant, low rate of oxygen leakage into the syste m. Similar results were obtained with the facultatively fermentative yeast Candida utilis. When the same experimental setup was used for anaerobic cul tivation, in complex YPD medium, Z. bailii exhibited exponential growth and vigorous fermentation, indicating that a nutritional requirement for anaer obic growth was met by complex-medium components. Our results demonstrate t hat restriction of oxygen entry into foods and beverages, which are rich in nutrients, is not a promising strategy for preventing growth and gas forma tion by Z. bailii. In contrast to the growth of Z, bailii, anaerobic growth of S. cerevisiae on complex YPD medium was much slower than grow-th is syn thetic medium, which probably reflected the superior tolerance of the forme r yeast to organic acids at low pH.