IJCA - Volume 3 - Flipbook - Page 63
2024 | Volume 3, Issue 1
laboratory must collect a minimum of 10 different kinds
of samples of vanilla ice cream to ensure a variety
representative of what would typically be received by the
laboratory. These samples may include ice creams from
different batches (lots), manufacturers, production days,
etc. Collecting more than 10 samples is advisable to
ensure an adequate variety.
61
Figure 5. Lowest Inter-laboratory reproducibility
standard deviation (sR) mean value validation study.
Overnight, a culture of Enterobacteriaceae is grown,
followed by serial dilutions and plating to determine
inoculation levels. Each of the 10 (or more) test
portions of vanilla ice cream undergoes thorough
homogenization and is then divided into two test
portions: A and B. Each set of test portions is then
inoculated with a range of contamination levels
typically found in samples routinely analyzed in the
laboratory (between 30 cfu/g – 30,000 cfu/g). Since
this study is conducted within one laboratory, it is
crucial to ensure that the analysis of the test portions
A and B differs in as many ways as possible: using
different technicians, incubators, batches of culture
media (different preparations from the same batch of
media powder), etc.
Each test portion is then analyzed using the Neogen
Petri昀椀lm Enterobacteriaceae Count Plate method.
Results are recorded and used to calculate the intralaboratory reproducibility standard deviation (sIR)
using the formula provided in the standard or using
the Excel® -based program (workbook) available on
the ISO TC34/SC9 website.
Within the validation study report for the Neogen
Petri昀椀lm Enterobacteriaceae Count Plate method,
locate the lowest Inter-laboratory reproducibility
standard deviation (sIR) mean value of the (food)
items used in the validation study and compare this
to the calculated sIR obtained in the veri昀椀cation
study. In Figure 5, the lowest sIR mean value in the
validation study for this method was found to be
0.125 (0.126 [low] + 0.122 [medium]+ 0.126 [high]) =
0.374 [total]) / 3 = mean value = 0.125).
The sIR must be ≤ 2 x the lowest sIR to meet the
implementation veri昀椀cation Acceptability Limits
(again, per Table 16 in the standard). The result
obtained in the study for sIR was 0.17, which is ≤ 2 x
0.125 sR, successfully completing the implementation
veri昀椀cation of this method. Figure 6 illustrates the
results using the Excel® -based program (workbook)
from the ISO TC34/SC9 website, after inputting all the
evaluation data.
Figure 6. Quantitative implementation veri昀椀cation results: sIR using the Excel®-based program
on ISO TC34/SC9 website
