Related Experiment Videos
Plating medium pH as a factor in apparent survival of sublethally stressed yeasts
Abstract:
Sublethally stressed cells of 9 of 10 species of yeast were recovered at maximum levels when potato dextrose agar was adjusted to approximately pH 8. The optimum for candida utilis was at approximately pH 10. At pH 3.5, as commonly employed with media selective for yeasts and molds, recovery of heat-stressed organisms ranged from essentially the same as at optimum pH to levels of 1% or less of the maximum count. The extent to which this may be of practical significance in assessing the microbiological quality of food products remains to be determined.
Insights
Alkaline conditions (pH 8) significantly improve yeast recovery after sublethal stress. Standard acidic media (pH 3.5) drastically reduce viable yeast counts, impacting food quality assessments.
Area of Science:
- Microbiology
- Food Science
- Yeast Physiology
Background:
- Sublethal stress affects yeast viability.
- Standard microbiological media often use acidic pH (3.5) for selectivity.
- Yeast recovery rates can be influenced by environmental factors like pH.
Purpose of the Study:
- To determine the optimal pH for recovering sublethally stressed yeast cells.
- To compare yeast recovery at alkaline pH versus standard acidic conditions.
- To assess the implications for microbiological quality testing of food products.
Main Methods:
- Yeast cultures from 10 species were subjected to sublethal stress.
- Recovery of stressed yeast cells was assessed on potato dextrose agar adjusted to various pH levels.
- Specific focus on recovery at pH 8 and pH 10 for Candida utilis.
Main Results:
- Maximum recovery for 9 out of 10 yeast species occurred at approximately pH 8.
- Candida utilis showed optimal recovery at approximately pH 10.
- At pH 3.5, recovery of heat-stressed yeasts was drastically reduced, often to 1% or less of maximum counts.
Conclusions:
- Alkaline pH significantly enhances the recovery of sublethally stressed yeast cells.
- Current acidic media practices may underestimate yeast populations in food samples.
- Further research is needed to understand the practical impact on food microbiological quality assessment.