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782 

B

ird

et al

.

:

J

ournal of

AOAC I

nternational

V

ol

. 98, N

o

. 3, 2015

solidify in the 3M Petrifilm RYM Count Plate medium. Several

laboratories also indicated that the colonies were very easy to

interpret due to their size and color. One laboratory indicated

that the “Space saving benefits of Petrifilm over the traditional

FDA BAM method are readily apparent.”

During the analysis of samples, several laboratories indicated

deviating from the approved protocol and therefore, their

data was subsequently removed from statistical analysis. No

laboratories were removed from statistical analysis as a result

of their data. For the raw ground beef, four laboratories were

removed from statistical analysis. Laboratory 12 was unable to

enumerate samples by both the 3M Petrifilm RYM Count Plate

method and reference methods on the same day. All samples

were plated onto DRBC, then stored at 2–8°C overnight and

plated onto the Petrifilm RYM plates the following day.

Laboratories 6 and 8 prepared the reference method samples

using duplicate plating and not the required triplicate plating.

Laboratory 4 (for both raw ground beef and raw almonds) failed

to enumerate the 3M Petrifilm RYM Count Plates at the 60 h

time point. Due to these deviations, these laboratories were

removed from statistical analysis.

There were no statistically significant differences at the

5% level in log transformed means between the 3M Petrifilm

RYM Count Plate method and FDA BAM/ISO 21257 methods

for either matrix evaluated in this study, at any of the three

contamination levels. No statistically significant differences

were observed between the 3M Petrifilm RYM Count Plate

results when enumerated at 48 h versus 60 h and compared to

the FDA BAM/ISO 21527 methods. No statistically significant

differences were also observed between 3M Petrifilm RYM

Count Plates that were incubated at 25°C and 28°C when

compared to the FDA BAM/ISO 21527 methods. Based on

the data presented, the s

r

values obtained at all incubation

conditions and for all three contamination levels were generally

similar between the two methods.

For raw frozen ground beef patties and raw almonds, the 3M

Petrifilm RYM Count Plate method was more repeatable than

the FDA BAM/ISO 21527 reference methods for one of the

six contamination levels analyzed at 25°C and four of the six

contamination levels analyzed at 28°C.

Recommendations

It is recommended that the 3M Petrifilm Rapid Yeast and

Mold Count (RYM) Plate method be adopted as Official First

Action status for the enumeration of yeast and molds in the

following high water activity matrixes: yogurt (1.5% fat),

frozen bread dough, fermented salami, sour cream, ready-made

pie, raw frozen ground beef patties (77%), ready-to-eat deli

sandwiches, sliced apples, and the following low water activity

matrixes: raw almonds and dehydrated soup.

Acknowledgments

We would like to extend a sincere thank you to the following

collaborators for their dedicated participation in this study:

Dave Metzger, Wendy Lee, and Thomas Hirsch, Accelerated

Analytical, Milwaukee, WI

Peyman Fatemi and Sharon Spencer, Aemtek, Inc., Fremont,

CA

Joel Blumfield, EDL Labs, Inc., Purvis, MS

Bryan Dieckleman, Eurofins Microbiology Laboratories,

Inc., Des Moines, IA

Karilyn Gonzales and Chelsea Fagundes, Food

Microbiological Laboratories, Inc., Cypress, CA

Jerry Reed and Jeraldine Medellin, Metrix 360 Laboratories,

San Antonio, TX

Adam Hankins, McCoy and McCoy Laboratories, Inc.,

Madisonville, KY

Figure 1: 3M Petrifilm RYM Count Plate vs. FDA BAM/ISO 21527 Results for Frozen Raw

Ground Beef Patties Incubated at 25

o

C and Enumerated at 48 and 60 Hours

2.00

2.50

3.00

3.50

4.00

4.50

5.00

2.00

2.50

3.00

3.50

4.00

4.50

5.00

Log1 3M RYM CFU/g Results

Log10 FDA BAM/ISO 21527 CFU/g Results

3M Petrifilm RYM Count Plate vs. FDA BAM/ISO

21527 for Raw Ground Beef Incubated at 25

o

C

Frozen Raw Ground Beef Patties

25C Enumerated at 48 Hours

Frozen Raw Ground Beef Patties

25C Enumerated at 60 Hours

Figure 1. 3M Petrifilm RYM Count Plate versus FDA BAM/ISO

21527 results for frozen raw ground beef patties incubated at 25°C

and enumerated at 48 and 60 h.

Figure 2: 3M Petrifilm RYM Count Plate vs. FDA BAM/ISO 21527 Results for Frozen Raw

Ground Beef Patties Incubated at 28

o

C and Enumerated at 48 and 60 Hours

2

3

4

5

2

2.5

3

3.5

4

4.5

5

g

10

3M RYM CFU/g Results

Log

10

FDA BAM/ISO 21527 CFU/g Results

3M Petrifilm RYM Count Plate vs.

FDA BAM/ISO 21527 for Raw Ground Beef

Incubated at 28

o

C

Frozen Raw Ground Beef Patties

28C Enumerated at 48 Hours

Frozen Raw Ground Beef Patties

28C Enumerated at 60 Hours

Figure 2. 3M Petrifilm RYM Count Plate versus FDA BAM/ISO

21527 Results for frozen raw ground beef patties Incubated at 28

°

C

and Enumerated at 48 and 60 h.

Figure 3: 3M Petrifilm RYM Count Plate vs. FDA BAM/ISO 21527 Results for Raw Almonds

Incubated at 25

o

C and Enumerated at 48 and 60 Hours

2.00

2.50

3.00

3.50

4.00

4.50

5.00

2.00

2.50

3.00

3.50

Log1 3M RYM CFU/g Results

Log10 FDA BAM/ISO 21527 CFU/g Results

3M Petrifilm RYM Count Plate vs. FDA BAM/ISO

21527 for Raw Almonds Incubated at 25

o

C

Frozen Raw Almonds 25C

Enumerated at 48 Hours

Frozen Raw Almonds 25C

Enumerated at 60 Hours

Figure 3. 3M Petrifilm RYM Count Plate versus FDA BAM/ISO

21527 results for raw almonds incubated at 25

°

C and enumerated at

48 and 60 h.

Figure 4: 3M Petrifilm RYM Count Plate vs. FDA BAM/ISO 21527 Results for Raw Almonds

Incubated at 28

o

C and Enumerated at 48 and 60 Hours

2.00

3.00

4.00

5.00

2.00

2.50

3.00

3.50

Log

10

3M RYM CFU/g

Results

Log

10

FDA BAM/ISO 21527 CFU/g Results

3M Petrifilm RYM Count Plate vs. FDA BAM/ISO 21527 for Raw

Almonds Incubated at 28

o

C

Raw Ground Beef 28C Enumerated

at 48 Hours

Raw Ground Beef 28C Enumerated

at 60 Hours

Figure 4. 3M Petrifilm RYM Count Plate versus FDA BAM/ISO

21527 results for raw almonds incubated at 28

°

C and enumerated at

48 and 60 h.