249 / 350
B
ird
et al
.:
J
ournal of
AOAC I
nternational
V
ol
.
98, N
o
. 3, 2015
771
(
4
) Lift the top of the film. Dispense 1 mL of each dilution
onto the center of the bottom film of each plate.
(
5
) Roll the film down onto the sample.
(
6
) Place the 3M Petrifilm Flat Spreader (Cat. No. 6425) on
the center of the plate. Press gently on the center of the spreader
to distribute the sample evenly. Spread the inoculum over the
entire 3M Petrifilm RYM Count Plate growth area before the gel
is formed.
Do not slide the spreader across the film.
(
7
) Remove the spreader and leave the plate undisturbed for
at least 1 min to permit the gel to form.
(
8
) Incubate the 3M Petrifilm RYM Count Plates at 25 or
28°C in a horizontal position with the clear side up in stacks
of no more than 40. Enumerate plates after 48 h of incubation.
If colonies appear faint, allow up to an additional 12 h of
incubation time for enhanced interpretation. 3M Petrifilm RYM
Count Plates can be counted using a standard colony counter
with the use of a back light or an illuminated magnifier to assist
with the estimated enumeration.
(
9
) Yeast colonies appear raised and small with defined
edges. Colonies may appear pink/tan to blue/green in color.
(
10
) Mold colonies appear flat with a dark center and
diffused edges. Colonies may appear blue/green to variable
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.
Table 2014.05C. Results of aerobic plate count for
collaborating laboratories
Lab
Frozen raw ground beef, CFU/g
Raw almonds, CFU/g
1
3.8
×
10
2
6.0
×
10
1
2
1.1
×
10
3
6.0
×
10
2
3
<10
3.0
×
10
1
4
Not reported
Not reported
5
2.8
×
10
3
2.8
×
10
1
6
8.0
×
10
1
2.2
×
10
1
7
9.1
×
10
2
1.6
×
10
2
8
Not reported
Not reported
9
9.0
×
10
2
2.0
×
10
2
10
1.3 x 10
3
4.0
×
10
2
11
>2500
1.0
×
10
1
12
Not reported
7.0
×
10
1
13
9.5
×
10
1
1.0
×
10
1
14
7.3
×
10
2
2.3
×
10
2
15
3.7
×
10
2
8.0
×
10
1