Matrix extension study: validation of compact dry YM for enumeration of yeast and mold in selected foods: modification to AOAC Performance Tested Method[SM] 100401

Nissui Compact Dry YM was originally certified by the AOAC Research Institute Performance Tested Methods[SM] (PTM) program (PTM No. 100401) for enumeration of yeasts and molds in fruit products after 7 days of incubation. A matrix extension study, organized by Campden BRI (Chipping Campden, United Kingdom), was conducted to extend the method's claim to cooked deli turkey, fresh whole tomatoes, cheese (Wensleydale), sliced white bread, and mayonnaise. In addition, the method was evaluated at 3 and 7 days to validate the 3 day incubation period. Compact Dry YM is a ready-to-use dry media sheet, containing a cold-soluble gelling agent, selective agents, and chromogenic medium, which are rehydrated by adding 1 mL diluted sample. Yeasts and molds appear as blue colonies, while molds can also have a cottony appearance and the color may vary. Users can obtain total yeast and mold count following 3-7 days of incubation at 25 [+ or -] 1[degrees]C. Method comparison data for cooked deli turkey, fresh whole tomatoes, cheese (Wensleydale), sliced white bread, and mayonnaise were collected in a single-laboratory evaluation by Campden BRI. A multilaboratory study was conducted on orange juice with 10 laboratories participating including the organizing laboratory. Compact Dry YM was compared to ISO 21527-1:2008, Microbiology of food and animal feeding stuffs-Horizontal method for the enumeration of yeasts and molds--Part 1: Colony count technique in products with water activity greater than 0.95, the current standard at the time of this study. Each matrix was evaluated for total yeasts and molds at each contamination level (including an uncontaminated level). In the single-laboratory evaluation (cooked deli turkey, fresh whole tomatoes, cheese, sliced white bread, and mayonnaise), colony counts were logarithmically transformed, and then the data were analyzed at each level for repeatability ([s.sub.r]), RSD of repeatability ([RSD.sub.r]), and mean difference between methods with a 95% confidence interval (CI). A CI outside a range of (-0.5 to 0.5) on the [log.sub.10] mean difference between methods was used as the criterion to establish a significant statistical difference. In the multilaboratory study on orange juice, after logarithmic transformation the data were analyzed for [s.sub.r], [RSD.sub.r], and mean difference with 95% CIs and also for reproducibility (s.sub.R]) and RSD of reproducibility (RSDR). Regression analysis was performed on all matrixes and reported a