Purpose: The purpose of this evaluation was to inter-laboratory evaluate the new method in comparison to the standard plate count (SPC) and AOAC 986.33 reference methods in pasteurized dairy products, ground beef and using environmental sponge samples.
Methods: Dairy products were evaluated at 32°C for 48 h. Whole milk (3.3% fat), chocolate milk (2% fat), heavy cream (20% fat), and skim milk (1% fat) were inoculated with a variety of stressed bacterial strains at 5 contamination levels. Five laboratories received 5 replicates from each level. All samples were decimal diluted and tested in duplicate. Ground beef and stainless steel surfaces were inoculated to low, medium and high concentrations. Ground beef extract (50 g/450 ml) and 25 ml sponge-surface-extracts were tested (n = 5 pairs) at 35°C for 48 h by two laboratories.
Results: Colony counts (CFU/ml or g) were evaluated for repeatability (Sr) and by paired t-test for statistical difference, > 0.5 log. The Peel Plate AC was not significantly different from the reference methods in the whole milk, chocolate, cream, ground beef and surface evaluations. Both Peel Plate AC and AOAC 986.33 methods showed > 0.5 log statistically lower results in the skim milk study indicating a better resuscitation of stressed bacteria by the SPC method. Replicate pairs from Peel Plate AC had similar Sr as both reference methods.
Significance: Peel Plate AC aerobic bacteria determination (32°C for 48 h) was equivalent to reference methods in most dairy preparations tested. At 35°C for 48 h, the new method performed similarly with ground beef and environmental sponge samples. Peel Plate AC offers a new testing alternative for aerobic plate count determination in dairy and food production.