339 / 350
sour cream at the low and medium inoculation levels at both time points, the Petrifilm RYM method had
1
better repeatability. The reference methods had better repeatability at the high inoculation level. For
2
sandwiches, the Petrifilm RYM method had better repeatability at the high inoculation level at both 48
3
and 60 hours, whereas the reference methods had better repeatability at the low and medium
4
inoculation levels at both time points.
5
There was no recovery of the inoculated organism (
Paecilomyces
spp) on the reference medium (DG-18)
6
from dehydrated soup. Five lots of dehydrated soup, with increasing inoculation levels, were tested in
7
an attempt to gain recovery of the target organism recovery on DG-18. In addition, prepoured DG-18
8
agar medium was utilized instead of the dehydrated, laboratory made medium as another attempt to
9
recover the target organism. The General Referee was contacted for advice. The decision was made
10
that since the
Paecilomyces
spp was not recovered with attempts to increase the inoculums titer that
11
the data would be accepted with no recovery from the DG-18 reference medium. There is no
12
explanation for why the DG-18 reference medium does not recover the organism from dehydrated soup.
13
The organism does grow on the medium when grown in pure culture.
14
15
In strain studies, of the 19 yeast and 23 mold strains that should have been detected by the 3M Petrifilm
16
RYM Plate method, all were detected and had appropriate colonial morphology, giving a sensitivity of
17
100%. Of the 4 non-target organisms that should not been detected the 3M Petrifilm RYM Plate method,
18
none of the 4 strains were detected, yielding a specificity of 100%. The 3M Petrifilm RYM Plate has a
19
shelf life of 18 months when stored at 2-8°C. A combined lot-to-lot and stability study has begun on
20
three unique lots of Petrifilm RYM Plates. At time 0, there was no difference in the performance of the
21
product with regard to lot or age of the product. The study is continuing and the results will be reported
22
as they become available.
23
Method ruggedness was demonstrated for three test parameters including incubation temperature,
24
incubation time, and water for rehydration.
25
26
Summary of Validated Performance Claims
27
The 3M Petrifilm RYM Plate method is used for the enumeration of yeast and mold in the food and
28
beverage industries and has been validated for yogurt, sour cream, almonds, sliced apples, frozen bread
29
dough, ready-made pie, sandwiches, dehydrated soup, fermented salami and frozen ground beef
30
patties. A t-test was performed using the appropriate assumption for equal or unequal variance to
31
43
AOAC Research Institute
Expert Review Panel Use Only
OMAMAN-16D/ PTM Report
ERP Use Only - December 2014