4. AOACRIMicroMethods-2018Awards

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772  B ird et al . : J ournal of AOAC I nternational V ol . 98, N o . 3, 2015

The 3M Petrifilm RYM Count Plate results along with FDA BAMand ISO results reported by each laboratorywere converted to logarithmic values for statistical analysis and were plotted using a Youden’s plot ( see Figures 1–4). The log 10 individual lab results are presented in Tables 2–9. Using the Youden’s plots, an initial review of the data to determine outliers was conducted by observing the mean replicate results for each laboratory at each contamination level for each matrix. The transformed data was than statistically analyzed for outliers by the Cochran and Grubb’s tests. No evidence of physical cause or suspicion of cause was noted, so all outliers identified were included in the statistical analysis. A paired t -test, the difference of means, and the reverse transformed mean difference were calculated on each contamination level for each matrix to determine if a statistically significant difference existed between the methods. Repeatability (s r ), s R , RSD r , and RSD R were determined for each contamination level for both the 3M Petrifilm RYM Count Plate and FDA BAM/ISO 21527 methods. The results of the interlaboratory data analyses are presented in Tables 2014.05A and 2014.05B . The result for each collaborating laboratory’s aerobic plate count analysis for each matrix is presented in Table 2014.05C . Frozen raw ground beef patties test portions were inoculated at a low, medium and high contamination level and were analyzed (Tables 2–5) for the enumeration of yeast and mold. Uninoculated controls were included in each analysis. Fifteen laboratories participated in the analysis of this matrix. 3M RYM Count Plate incubated at 25 ° C and enumerated at 48 h.— The mean log 10 counts of the 3M Petrifilm RYM Count Plate and FDA BAM/ISO 21527 results were compared Table 1. Participation of each collaborating laboratory a Laboratory Raw ground beef Almonds 1 Y Y 2 Y Y 3 Y Y 4 Y b Y b 5 Y Y 6 Y b Y 7 Y Y 8 Y b Y 9 Y Y 10 Y Y 11 Y Y 12 Y b Y 13 Y Y 14 Y Y 15 Y Y a  Y= Collaborator analyzed the food type; N= collaborator did not ana- lyze the food type. b  Results were not used in statistical analysis due to deviation of testing protocol or laboratory error. Frozen Raw Ground Beef Patties (77% Lean)

upon prolonged incubation. See Table 2014.05D for yeast and mold appearance. ( 11 ) The circular growth area is approximately 30 cm 2 . Plates containing greater than 150 colonies can be either estimated or recorded as TNTC (too numerous to count). 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 will need to be retested at higher dilutions. When the sample contains substantial amounts of mold, depending on the type of mold, the upper countable limit may be at user discretion. ( 12 ) Food samples may occasionally show interference on the 3M Petrifilm RYM Count Plates, for example: ( a ) Uniform blue background color (often seen from the organisms used in cultured products). These should not be counted as TNTC. ( b ) Intense pinpoint blue specks (often seen with spices or granulated products). ( c ) Report final results as colony-forming units/gram (CFU/g). ( 13 ) If required, colonies may be isolated for further identification by direct microscopy or biochemical analysis. Lift the top film and pick the colony from the gel. In this collaborative study, the 3M Petrifilm RYM Count Plate method was compared to two reference methods for enumerating total yeast and mold: FDA BAM Chapter 18 and ISO 21527 Part 1 or Part 2. A total of 15 laboratories throughout the United States participated, with 11 laboratories submitting valid data for the frozen raw ground beef patties and 14 laboratories submitting valid data for the raw almonds as presented in Table 1. For the frozen raw ground beef patties, laboratories 4 (failed to enumerate 3M Petrifilm RYM Count Plates at 60 h), 6 and 8 (plated the reference method samples in duplicate and not the required triplicate plating) and 12 [plated the 3M Petrifilm RYM Count Plates and reference method plates on two different days (enrichments were held at 2–8°C overnight and the 3M Petrifilm RYM Plates were plated 24 h after the reference method plates)] reported deviations from the protocol and were therefore excluded from statistical analysis. For the raw almonds, laboratory 4 reported a deviation from the protocol (failure to enumerate 3M Petrifilm RYM Count Plates at 60 h) and was therefore excluded from the statistical analysis. Table 2014.05D. Appearance of yeast and mold on 3M Petrifilm RYM Plates Yeast Mold Small colonies Large colonies Colonies have defined edges Colonies have diffused edges Pink/tan to blue/green in color Blue/green to variable upon pro- longed incubation Colonies appear raised (3-dimensional) Colonies appear flat Colonies have a uniform color Colonies have a dark center with diffused edges Results of the Collaborative Study

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