Purpose: Independently evaluate PP-YM in comparison to the FDA BAM Chapter 18 method using, dichloran rose bengal chloramphenicol (DRBC) agar, in milk, mixed fruit and environmental sponge samples.
Methods: Milk (2% fat), mixed fruit (100% fruit juice) and stainless steel surfaces were artificially contaminated with fungal strains in both the manufacturer and independent laboratory, Q laboratories Inc. Target contamination levels for spiked samples at low, medium and high levels were split into n=5 replicates. All samples were decimally diluted and tested in duplicate. Foods were homogenized (25 g/225 ml) in 0.1% peptone water (PW), and neutralizing broth sponge-surface-swabs were homogenized with PW. The candidate method tested 1 ml of sample dilution and the standard method tested 0.1 ml from dilutions. PP-YM plates were evaluated at 72 h and 120 h incubation at 25°C, and DRBC plates after 120 h at 25°C.
Results: Colony counts (CFU/ml or g) were evaluated for repeatability (Sr) and by paired-t-test for statistical difference, defined as 95% confidences outside 0.5 log the reference method. The PP-YM after 5 days incubation was not-significantly different at the 95% level from the FDA-BAM at most levels of the fruit, surface evaluations and milk. Milk at some of the spike levels was an exception in the manufacturer’s laboratory.
Significance: PP-YM detected fungal contamination similarly to the reference method (25°C for 3-5 days) in food and surfaces tested. PP-YM offers a new testing alternative for fungi detection in foods and food production surfaces.