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

Abstract

The effects of temperature (8 and 22 °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 °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 °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.