Evaluation of a Culture Film (Petrifilm YM) Method for Enumerating Yeasts and Molds in Selected Dairy and High-Acid Foods.

The Petrifilm Yeast and Mold (YM) plate was compared to acidified potato dextrose agar (APDA) and chloramphenicol-supplemented plate count agar (CPCA) using pour- and surface-plating techniques for its ability to recover yeasts and molds from hard and soft cheeses, cottage cheese, yogurt, sour cream, fruit juice, salad dressing, relishes, and tomato-based sauces. Correlation coefficients of Petrifilm YM plates versus pour-APDA, surface-APDA, pour-CPCA, and surface-CPCA for recovering total yeasts and molds from a composite of the eight test foods were, respectively, 0.993, 0.993, 0.994, and 0.995. Slope and intercept values for populations detected using Petrifilm YM plates versus traditional systems ranged, respectively, from 0.984 to 1.008 and -0.051 to 0.149. The coefficient of variation for total yeast and mold populations recovered on Petrifilm YM plates was 1.0% compared to 1.2 to 1.7% for traditional enumeration systems. Regardless of the enumeration system employed or the type of fungal cell, i.e., yeast or mold, being enumerated, significantly (P ≤ 0.05) higher populations were generally detected after 5 d compared to 3 d of incubation. After 5 d of incubation, in no case were yeast or total yeast and mold populations detected in the eight food products using Petrifilm YM plates significantly lower than respective populations detected using traditional pour- and surface-plating techniques and media. When Petrifilm YM plates were used, significantly higher total yeast and mold populations were detected in 3, 1, and 1 out of eight food products compared to using, respectively, pour-APDA, surface-APDA, and surface-CPCA enumeration systems. The Petrifilm YM plate offers an acceptable alternative to traditional methods for enumerating yeasts and molds in the dairy and high-acid products evaluated in this study.