Food spoilage yeasts: effects of pH, NaCl and temperature on growth

The effects of temperature (8 and 22 degrees C), pH (2.5-6.0) and NaCl concentration (0.4-8% w/v) were evaluated on the time to growth for 13 strains of yeasts representing five genera: Debaryomyces, Pichia, Zygosaccharomyces, Candida and Saccharomyces. Laboratory media were made at various combinations of the three factors, inoculated with the individual yeasts, incubated for up to a maximum of 56 days and observed for signs of turbidity. At 22 degrees C, 12 of the 13 yeast species tested were able to grow at 8% NaCl, although the rate of growth varied considerably, taking between 1 day (Candida guilliermondii) and 32 days (Candida holmii) to reach turbidity. All 13 species were able to grow at pH 2.5, although the maximum NaCl concentration permitting growth at this pH ranged from 0.8% (Debaryomyces sp.) to 8% (eight species). When the temperature was reduced to 8 degrees C, the maximum salt level permitting growth was generally lower and only five species were able to grow at 8% NaCl. In addition, the minimum pH permitting growth was increased and only 10 of the 13 species grew at pH 2.5. It was evident that there was a synergistic effect between NaCl and pH at the lower temperature. For example, for Candida parapsilosis the maximum NaCl concentration permitting growth was 6.4, 4.8, 3.2 and 1.6% when the pH was 4.5, 4, 3.5 and 3 respectively. These data have an application to producers of low pH chilled products and could be used to assess the spoilage potential of new and existing product formulations. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.