Use of Accuracy Profile for Validation of Petrifilm Rapid Yeast and Mold Count Plate for Enumeration of Yeast and Mold in Beverage

Abstract

       Validation of quantitative method in microbiology according to ISO 16140 - 2:2016 specifies use of accuracy profile to compare the result of reference and alternative methods. The accuracy profile was used to validate the Petrifilm^TM Rapid Yeast and Mold Count Plate (3M RYM) by comparing yeast and mold counts in liquid beverages with the US FDA BAM procedure recognized as reference method. The test samples were naturally and artificially contaminated at low level (1 - 100 CFU/ml), medium level (100 - 1,000 CFU/ml), and high level (>1,000 CFU/ml). When incubated at 25°C and 28°C for 48 h and 72 h, the results of the two methods showed relationship as linear and the Petrifilm 3M RYM gave Pearson’s correlation coefficient scores close to 1, i.e. 0.9986, 0.9988, 0.9995 and 0.9992, respectively. The accuracy profile for validation of Petrifilm 3M RYM was accomplished by setting the β-expectation tolerance intervals (β-ETI) at 80% (β%) and the acceptability limits, AL (λ) at ±0.3 and ±0.5 log₁₀ CFU/ml. For a λ of ±0.5 log₁₀, the 3M method incubated at 25°C and 28°C for 48 h and 72 h, the β-ETI limits were within the acceptability limits at all contamination levels. When λ was ±0.3 log₁₀, only at 25°C and 28°C, 72 h that the β-ETI limits fell inside the acceptability limits at all contamination levels. It can be concluded that the validity of Petrifilm 3M RYM depends on defined β% and acceptability limits (λ) specified by the users. Use of accuracy profile assists the users to choose an analytical method appropriately.