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© 2015 AOAC INTERNATIONAL
supplemented with antibiotics, a cold-water-soluble gelling agent,
and an indicator system that facilitates yeast and mold enumeration.
3M Petrifilm RYM Count Plates are used for the enumeration of
yeast and mold in as little as 48 h in the food and beverage industries.
3M Food Safety is certified to ISO (International Organization for
Standardization) 9001 for design and manufacturing.
B. Apparatus and Reagents
(
a
)
3M Petrifilm RYM Count Plate.
—25 plates/pouch; two
pouches/box (3M Food Safety, St. Paul, MN, USA).
(
b
)
Sterile diluents.—
0.1% peptone water.
(
c
)
Pipets.—
Capable of 1000 µL or a serological pipet.
(
d
)
Sterile pipet tips.—
Capable of 1000 µL.
(
e
)
Stomacher.—
Seward or equivalent.
(
f
)
Filter stomacher bags.
—Seward or equivalent.
(
g
)
3M Petrifilm Flat Spreader.
(
h
)
Incubators.—
Capable of maintaining 25 ± 1°C and 28 ± 1°C
and having a solid front to maintain a dark interior.
(
i
)
Refrigerator.—
Capable of maintaining 2–8°C, for storing the
3M Petrifilm RYM Plates.
(
j
)
L-shaped spreaders.
(
k
)
Standard colony counter or illuminated magnifier.
C. General Instructions
(
a
)
Store unopened 3M Petrifilm RYM Plate pouches
refrigerated or frozen (–20 to 8°C/–4 to 46°F). Just prior to use,
allow unopened pouches to come to room temperature before
opening (20–25°C/<60% RH). Return unused 3M Petrifilm RYM
Plates to the pouch. Seal by folding the end of the pouch over
and applying adhesive tape. To prevent exposure to moisture, do
not refrigerate opened pouches. Store resealed pouches in a cool
dry place (20–25°C/<60% RH) for no longer than 4 weeks. It is
recommended that resealed pouches of 3M Petrifilm RYM Plates
be stored in a freezer if the laboratory temperature exceeds 25ºC
(77ºF) and/or the laboratory is located in a region where the relative
humidity exceeds 60% (with the exception of air-conditioned
premises).
To store opened pouches in a freezer, place 3M Petrifilm RYM
Plates in a sealable container.
Post-incubation 3M Petrifilm RYM Plates can be stored at –10 to
–20°C for up to 7 days.
(
b
)
Follow all instructions carefully. Failure to do so may lead
to inaccurate results.
Table 2014.05B. Interlaboratory study results of 3M Petrifilm RYM versus FDA-BAM and ISO 21527 methods for raw almonds
3M Petrifilm RYM method
FDA-BAM/ISO 21527 methods
a
Matrix
Lot
N
b
Mean
c
s
r
s
R
N
Mean
s
r
s
R
P
-value
d
Difference
of means
Reverse
transformed
mean
difference
e
Raw almonds
25
°
C, 48 h
Control
12(0)
<1.00
— — 12(0)
<1.00
— — — —
—
Low 14(0)
1.45
0.17
f
0.26
14(0)
1.55
0.19
0.34 0.4165
0.10
–7.30
Medium 14(1)
2.12
0.26
0.39
14(0)
2.21
0.20
0.24 0.3322
0.09
–30.36
High
14(2)
3.00
0.18
0.49
14(1)
3.08
0.12
0.31 0.2833
0.08
–202.26
25
°
C, 60 h
Control
12(0)
<1.00
— — 12(0)
<1.00
— — — —
—
Low 14(0)
1.53
0.23
0.28
14(0)
1.55
0.19
0.34 0.8391
0.02
–1.60
Medium 14(0)
2.20
0.21
0.27
14(0)
2.21
0.20
0.24 0.7789
0.01
–3.69
High
14(2)
3.04
0.18
0.41
14(1)
3.08
0.12
0.31 0.5418
0.04
–105.79
28
°
C, 48 h
Control
12(0)
<1.00
— — 12(0)
<1.00
— — — —
—
Low 14(0)
1.58
0.16
f
0.21
14(0)
1.55
0.19
0.34 0.7381
0.03
2.54
Medium 14(0)
2.17
0.17
f
0.29
14(0)
2.21
0.20
0.24 0.6139
0.04
–11.73
High
14(2)
3.01
0.17
0.45
14(1)
3.08
0.12
0.31 0.3904
0.07
–178.97
28
°
C, 60 h
Control
12(0)
<1.00
— — 12(0)
<1.00
— — — —
—
Low 14(0)
1.60
0.17
f
0.20
14(0)
1.55
0.19
0.34 0.5474
0.05
4.33
Medium 14(0)
2.21
0.17
f
0.23
14(0)
2.21
0.20
0.24 0.9483
0.00
0.00
High
14(2)
3.03
0.18
0.42
14(1)
3.08
0.12
0.31 0.4687
0.05
–130.75
a
Samples were analyzed by harmonized FDA-BAM Chapter 18 and ISO 21527 methods using 0.1% peptone as the sample diluent.
b
N
= Number of laboratories that reported complete results. Outliers are in parentheses.
c
Log
10
yeast and mold CFU/g.
d
Significant difference (
P
<0.05).
e
Results presented as CFU/g.
f
Results indicate that the candidate method is more repeatable than the reference methods. s
r
= Repeatability standard deviation; s
R
= reproducibility standard
deviation.