Rapid Quantitative Enumeration of Yeasts and Molds

Introduction: Yeast and Molds are ubiquitous food spoilage agents that can grow at a wide range of temperatures, pH values and more importantly at reduced water activities (A_w) thus having the potential for substantial economic losses to the food industry. These organisms have become important indicators for monitoring food quality but the 5-7 day incubation required by traditional enumeration methods poses a burden on food producers. A novel dehydrated film medium was developed to address the need for rapid (48-60 hours) detection of yeasts and molds and the detection technology was optimized to overcome the inherent limitations of yeast and mold appearance and interpretation on dehydrated media.

Purpose: This study was performed to demonstrate comparative enumeration of yeast and molds using a new dehydrated film medium and reference methodology as described in FDA/BAM and ISO21527:2008 (parts 1 and 2).

Methods: The method comparison was conducted using a variety of naturally contaminated food matrices (n = 75) with the new dehydrated film test method and a reference method (FDA/BAM and ISO21527:2008, parts A and B). Each food sample was serially diluted in 0.1% peptone water. The new dehydrated film medium was hydrated with 1ml of the sample and 100 micro-liters were spread plated on DRBC or DG-18 media in replicate.  

Results: Results were statistically comparable between the new dehydrated film method at 48-60 h to DRBC and DG-18 at 5 days with no significant differences as indicated by the P-values (> 0.05) and regression analysis.

Significance: Rapid quantitative detection of yeasts and molds using the new dehydrated film method was evaluated using a large number (n = 75) of naturally contaminated foods. The new method was found to be reliable and have improved interpretation thus providing end users with actionable results in a shorter time frame.