4. AOACRIMicroMethods-2018Awards

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20 (dairy products) or 40 for all other foods. Enumerate plates after 24 ± 2 h of incubation (or 48 ± 3 h in the case of dairy powders, including whey powder). 3MPetrifilmRAC 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. (i)  Enumerate all colonies regardless of size, color, or intensity. (j)  The circular growth area is approximately 30 cm 2 . Plates containing >300 colonies can be either estimated or recorded as TNTC. Estimation can only be done by counting the number of colonies in one or more representative squares and determining the average number per square. The average number can be multiplied by 30 to determine the estimated count per plate. If a more accurate count is required, the sample may need to be retested at higher dilutions. (k)  Average the counts between the replicate plates. Report final results as CFU per gram or milliliter (CFU/g or CFU/mL). Note : If there are two dilutions within the countable range, use the following calculation to determine the final count: N C 1.1 d ( ) = Σ × where, N is the number of colonies per milliliter or per gram of product, ΣC is the sum of all colonies on both plates, and d is the dilution from which first counts were obtained. (l)  Food samples may occasionally show interference on the 3M Petrifilm RAC Plates for example: ( 1 ) Uniform blue background color (often seen from the organisms used in cultured products). These should not be counted as TNTC. ( 2 ) Intense pinpoint blue specs (often seen with spices or granulated products). (m)  When necessary, colonies may be isolated for further identification test using standard procedures. Lift the top film and pick the colony from the gel.

shrimp) and SMEDP Chapter 6 (for instant NFDM). A total of 16 laboratories throughout the United States participated in the evaluation (all 16 laboratories participated in the evaluation of the raw easy-peel shrimp, with 15 laboratories participating in the evaluation of the pasteurized skim milk and instant NFDM) with 16 laboratories submitting data for raw easy-peel shrimp, 13 laboratories submitting data for the pasteurized skim milk, and 15 laboratories submitting data for the instant NFDM as presented in Table 2015.13C . For the raw easy-peel shrimp and dry milk power, all participating laboratories submitted data. For pasteurized skim milk, two laboratories reported deviations from the protocol and their data were not included in the statistical analysis. After receipt of samples, Laboratory 6 indicated that samples were stored at room temperature (24 ± 2°C) instead of refrigeration temperature (2–8°C) for 24 h prior to testing. Laboratory 7 reported that their samples were not received until after 48 h of shipment. The temperature control indicated the samples were at extremely elevated temperature (30°C). Both laboratories proceeded with sample analysis, however all samples analyzed produced results that were greater than the countable range (TNTC) for all dilutions and no data were submitted. The 3M Petrifilm RAC Plate results along with FDA BAM and SMEDP results reported by each laboratory were converted to logarithmic values for statistical analysis and plotted using a Youden plot. The Log 10 individual laboratory results are presented in Tables 2015.13D-G . Figures 1–4 present theYouden plots for each method for each matrix. Figures 5–8 present the mean Youden plots for 3M Petrifilm RAC and the reference methods. The transformed data were analyzed for outliers by Cochran and Grubbs’ tests. No evidence of physical cause or suspicion of cause was noted, so all identified outliers were included in the statistical  analysis. The difference of means and the reverse-transformed difference of means (including 95% CIs) were determined for each contamination level for each matrix to determine whether a statistically significant difference existed between the methods. s r and s R were determined for each contamination level for both the 3M Petrifilm RAC Plate and FDA BAM and SMEDP methods. The results of the

Results of the Collaborative Study

In this collaborative study, the 3M Petrifilm RAC Plate was compared with two reference methods for the enumeration of aerobic bacteria: FDA BAM Chapter 3 (for raw easy-peel

Figure 1. Youden plots for 3M Petrifilm RAC Plate and FDA BAM results for raw easy-peel shrimp evaluated at 32°C.

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