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Table 1) colonies by the Petrifilm RYM Plate method. There was no growth for any of the 4 non-target
1
(exclusivity) strains on the Petrifilm RYM Plate method
2
Method Comparison
3
A study was conducted to determine the ability of the Petrifilm RYM Plate method to recover and
4
enumerate yeasts and molds compared to the ISO 21527:2008 parts 1 and 2 and the FDA BAM Chapter
5
18.
6
Apparatus and Reagents
7
(a.)
3M Petrifilm Rapid Yeast and Mold Count Plate – Plates available from 3M Food Safety (St.
8
Paul, MN), contain chromogenic detection medium and a cold-water-soluble gelling agent.
9
(b.) Pipets – 1 mL serological pipette or calibrated 1.0 mL positive displacement pipettor, or 3M
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Electronic Pipettor and tips, or equivalent, may be used to deliver a 1.0 mL inoculum onto
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plates.
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(c.)
Plastic spreader – Flat spreader available from 3M Food Safety, catalog number 6425.
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(d.)
Incubator – Capable of maintaining 25° - 28° ± 1°C for 48 ± 1 hours.
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(e.) Colony Counter – Standard apparatus, Quebec Model, available from many suppliers, or one
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providing equivalent magnification and visibility.
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(f.) DRBC Agar
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(g.) Stomacher or equivalent
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(h.) Appropriate diluent as described in the 3M Petrifilm Yeast and Mold Count Plate Instructions
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for Use
20
21
For the method comparison analysis, ten matrices were tested from a single production lot: Yogurt,
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sour cream, almonds, sliced apples, frozen bread dough, ready-made pie, sandwiches, dehydrated soup,
23
fermented salami and frozen ground beef patties. For each matrix a minimum 3 lots were analyzed for
24
the presence of the target analytes. Matrices containing naturally occurring yeasts and molds were
25
temperature abused in order to get 3 distinctive lots. Naturally contaminated foods (frozen bread
26
dough, sliced apples, sandwiches) had a target contamination level of low (10-100 CFU/g), medium (100-
27
1,000 CFU/g), and high (1,000-10,000 CFU/g level). For the sliced apples naturally contaminated lots
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were held at 2-5°C for one week and diluted with uncontaminated product to reduce contamination
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levels. Frozen bread dough was diluted with uncontaminated product to reduce contamination levels.
30
The sandwiches were held at 2-5°C for 48 hours, for 1 to 2 weeks to achieve three separate lots of
31
contamination. A total of four lots each of artificially contaminated matrixes (yogurt, sour cream,
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almonds, ready-made pie, dehydrated soup, fermented salami and frozen ground beef patties), were
33
analyzed for the target analyte at the following target levels: uninoculated (0 CFU/g), low (10-100
34
CFU/g), medium (100-1,000 CFU/g) and high (1,000-10,000 CFU/g). Frozen beef patties, yogurt, and
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ready-made pie were inoculated with a broth culture. The broth culture was prepared by transferring a
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single colony to yeast mold (YM) broth for 48 hours at 30°C. The inoculated test portions were mixed
37
15
AOAC Research Institute
Expert Review Panel Use Only
OMAMAN-16D/ PTM Report
ERP Use Only - December 2014