Purpose: Validate rehydratable dry-film microbiological test methods for determination of Aerobic Bacteria (AOAC 990.12) and Total Coliforms (AOAC 991.14) in margarine against conventional media to assess validity and enhance credibility and confidence in the results obtained with these alternative methods.
Methods: A margarine matrix was inoculated with Escherichia coli ATCC 25992 at levels of 34 or 44 CFU/g and ten samples per media type (n = 20) were plated in duplicate according to AOAC 990.12 and AOAC 991.14 methods, respectively. Plate count agar plates (n = 20) were inoculated in duplicates at the same levels. Sterility of the margarine matrix was assessed by plating ten uninoculated margarine samples on each media type. All samples were incubated at 35°C. The results were compared to internal validation criteria for accuracy, reproducibility and uncertainty.
Results: There was no significant difference in microbial recovery from the margarine matrix observed between traditional media and methods AOAC 990.12 (P = 0.702) or AOAC 991.14 (P = 0.565). Results fell within established internal parameters for accuracy, reproducibility and uncertainty.
Significance: Methods AOAC 990.12 and 991.14 were validated internally as accurate, precise and as carrying an acceptable level of uncertainty when analyzing a margarine sample matrix. Rehydratable dry-film media constitutes a reliable and convenient alternative with validity comparable to traditional media for determining the microbiological quality of margarine.