Evaluation of a Compact Dry Plate Method for Enumeration of Yeasts and Molds in Foods during a Microval EN ISO 16140 Validation

Introduction: Compact Dry (Nissui Pharmaceutical Co. Ltd supplied by Hyserve Gmbh & Co. KG ) are ready-to-use dry media sheets comprising culture medium, soluble gel and chromogenic compounds. The sheets are rehydrated by inoculating them with 1 ml of diluted food. This study presents the results from comparing Compact Dry YM for yeasts and molds against the standard ISO method in a range of foods.

Purpose: Comparison of Compact Dry YM against the reference method (ISO 21527-1:2008) for enumeration of yeasts and molds using validation protocol EN ISO 16140.

Methods: Compact Dry YM was used to enumerate numbers of yeasts and molds present in 1 ml samples of diluted foods. The inoculate YM plates were incubated at 25°C for 3-7 days. The standard ISO method used 0.1 ml spread plates on DRBCA incubated at 25°C for up to 5 days. For the expert laboratory study, five inoculation levels in five food types were analysed by both methods; foods tested were meat products, fruit and vegetable products, dairy products, bakery products and mayonnaise. The interlaboratory study involved 9 laboratories in 5 countries. The results were analysed using the principles of EN ISO 16140.

Results: The correlation coefficient (R²) for all foods was 0.98. The interlaboratory study revealed no evidence of any differences in reproducibility in all levels or repeatability at the medium and high levels between the two methods. The selectivity (inclusivity/exclusivity) of YM was equal to the reference method. Compact Dry YM was found to be equivalent to the standard ISO method for enumeration of yeasts and mold in all foods with a water activity > 0.95.

Significance: Compact Dry YM gave comparable results to the reference method in a convenient ready-to-use format.