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3M™ Petrifilm™ Rapid Yeast Mold Count Plate
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AOAC Performance Tested Method
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Abstract
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The 3M™ Petrifilm™ Rapid Yeast Mold Count Plate (Petrifilm RYM) detects and enumerates yeast and
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mold from a variety of foods. Ten matrices – yogurt, sour cream, almonds, sliced apples, frozen bread
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dough, ready-made pie, sandwiches, dehydrated soup, fermented salami and frozen ground beef patties
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– were compared to the ISO 21527:2008 parts 1 and 2 and the FDA BAM Chapter 18 reference methods
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at 48 and 60 hours. Naturally contaminated samples that covered three levels of contamination (low
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level 10 -100 CFU/g, medium level 100-1,000 CFU/g, and a high level 1,000-10,000 CFU/g) were
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analyzed. Matrices that were not naturally contaminated were artificially contaminated with a yeast or
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mold, and five replicates were analyzed at four levels (uninoculated, low, medium, and high). The
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results demonstrated that the 3M Petrifilm RYM Plate method as shown to be equivalent to or better
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than the average log counts of the ISO 21527:2008 parts 1 and 2 and the FDA BAM Chapter 18 reference
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methods at 48 and 60 hours. In addition, the repeatability of the Petrifilm RYM method was equivalent
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to or better than the reference methods at both 48 and 60 hours. In the independent laboratory
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validation study, there was no significant difference in detection, enumeration, or repeatability between
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the Petrifilm RYM method and ISO 21527:2008 parts 1 and 2 and the FDA BAM Chapter 18 reference
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methods for yogurt at 48 and 60 hours. For frozen ground beef patties there was a significant difference
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between the Petrifilm RYM Plate method and the reference methods at 48 and 60 hours with the
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Petrifilm RYM method enumerating more organisms that the reference methods(p<0.05). In strain
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studies, of the 42 yeast and mold tested, all produced typical colonies on Petrifilm RYM Plate method.
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Of the 4 bacterial strains that should not have been detected by the Petrifilm RYM Plate method, all 4
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strains did not grow on the plate. Lot-to-lot study of Petrifilm RYM Plates was evaluated and showed no
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differences at time zero. In assay ruggedness studies, there was no difference in performance for three
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test parameters: incubation time, incubation temperature and type of diluents used to rehydrate the
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plate medium.
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AOAC Research Institute
Expert Review Panel Use Only
OMAMAN-16D/ PTM Report
ERP Use Only - December 2014