Evaluation of the Petrifilm Dry Rehydratable Film for the Enumeration of Yeasts and Moulds in Naturally Contaminated Foods

Abstract

Two hundred thirty‐seven samples from six food groups (tree nuts, grains and grain products, dried fruits, fresh produce, fruit juice and dairy products) were tested for levels of fungal contamination using the Petrifilm dry rehydratable film for yeast and mould (PYM ) enumeration (3M Microbiology, St. Paul, MN) and the Food and Drug Administration (FDA) official method. Results indicated that PYM performed very well for all tested commodities giving YM counts similar to those of the FDA method. Statistical analysis of the data (t‐test) revealed no significant differences between the two methods for all foods tested. Linear regression analysis showed that the correlation coefficients between the two methods were over 0.90 for 91% of the commodities tested. Some difficulties were encountered during counting of the colonies on PYM as yeast colonies on this medium tend to be very small with rather faded colorations. PRACTICAL APPLICATIONS Assessment of the efficacy of Petrifilm and determining its equivalence to traditional, validated methods will give the testing laboratories and the industry an alternate option for the enumeration of fungi in foods. The use of Petrifilm would be especially useful when analyst time is limited as it requires no media preparation and minimal time for sample inoculation.