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7 days and the need for rapid enumeration is critical to the food industry. The 3M
™
Petrifilm
™
1
Rapid Yeast and Mold Count (RYM) Plate uses a cold-water-soluble gelling agent and an
2
indicator system to facilitate the enumeration of yeast and molds after 48 hours of incubation.
3
The 3M Petrifilm RYM Count Plate allows for the simple and rapid enumeration of yeasts
4
and molds in the food and beverage industries. Samples are diluted in 0.1% peptone water and
5
a sample aliquot is plated onto the 3M Petrifilm RYM Count Plate. The sample aliquot is
6
dispersed throughout the growth area and the plates can be incubated at 25
o
C - 28
o
C.
7
Enumeration of colonies occurs in as little as 48 hours of incubation. If colonies appear faint, the
8
plates can be incubated up to an additional 12 hours for enhanced interpretation. The 3M
9
Petrifilm RYM Count Plate provides gridlines to assist with the enumeration.
10
Prior to the collaborative study, the 3M Petrifilm RYM Count Plate was validated according
11
to AOAC Validation Guidelines [3] in a harmonized AOAC Performance Tested Method
SM
12
(PTM) study. The objective of the PTM study was to demonstrate that the 3M Petrifilm RYM
13
Count Plate accurately detected and enumerated yeasts and molds in selected foods as claimed
14
by the manufacturer and that no difference in repeatability was observed between the 3M
15
Petrifilm RYM Count Plate method and the reference methods. For the 3M Petrifilm RYM
16
Count Plate PTM evaluation, ten (10) matrices were evaluated: yogurt (1.5% fat), sour cream,
17
raw almonds, sliced apples, frozen bread dough, ready-made cherry pie, ready-to-eat deli
18
sandwiches, dehydrated chicken noodle soup, fermented salami and raw frozen ground beef
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patties (77% lean).
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All other PTM parameters (inclusivity, exclusivity, ruggedness, stability and lot-to-lot
21
variability) tested in the PTM studies satisfied the performance requirements for PTM approval.
22
The method was awarded PTM certification number 121301 on December 18, 2013.
23
The purpose of this collaborative study was to compare the 3M Petrifilm RYM Count Plate to
24
a harmonized version of the U.S. Food and Drug Administration (FDA) Bacterial Analytical
25
Manual (BAM) Chapter 18: Yeasts, Molds and Mycotoxins [1] and the ISO 21527:2008
26
Microbiology of food and animal feeding stuffs – Horizontal method for the enumeration for
27
yeast and molds
– Part 1:
Colony count technique in products with water activity greater than
28
0,95
[4] and Part 2:
Colony count technique in products with water activity less than or equal to
29
0,95
[5] methods using 0.1% Peptone water as the diluent for raw almonds and raw frozen
30
ground beef patties (77% lean).
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32
Collaborative Study
33
34
Study Design
35
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In this collaborative study, two matrices, raw frozen ground beef patties (77% lean) and raw
37
almonds, were evaluated. The matrices were obtained from local retailers and screened for the
38
presence of yeast and molds by the BAM and ISO reference methods. The raw frozen ground
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beef patties were artificially contaminated with a yeast,
Trichosporon mucoides
American Type
40
Culture Collection (ATCC) 201382, and the almonds with a mold,
Aspergillus aculeatus
ATCC
41
56925. Four separate levels of contamination, including an uninoculated control level and 3
42
levels of artificial contamination, were evaluated for each matrix. The target for the three levels
43
of artificial contamination was as follows: low, 10-100 colony forming unit (CFU)/g; medium,
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100-1,000 CFU/g; high 1,000-10,000 CFU/g. Two replicate samples from each of the four levels
45
were analyzed by both the candidate and reference methods. One set of paired samples (8 total)
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per matrix was sent to each laboratory for analysis by the 3M Petrifilm RYM Count Plate and the
47
BAM and ISO reference methods. For both matrices, collaborators were sent an additional 60 g
48
test portion and instructed to conduct a total aerobic plate count (APC) using 3M Petrifilm
49
Candidates for 2016 Method of the Year
76