Validation of the Soleris® Yeast and Mold Test for Semiquantitative Determination of Yeast and Mold in Selected Foods

Abstract

The Soleris yeast and mold method, a growth-based test system with an optical detection end point, was evaluated for its ability to detect yeast and mold contamination in a wide variety of foods. The Soleris test was used in a semiquantitative manner, in which the test result is positive or negative at a threshold level determined by the dilution and volume of sample homogenate added to the Soleris test vial. By testing at two or more threshold levels, the contamination level can be estimated. The LOD of the Soleris method is 10 CFU/g when 1 mL of a 1:10 sample homogenate is added to the test vial. In these studies, the Soleris results were compared to plate counts obtained using the U.S Food and Drug Administration/Bacteriological Analytical Manual direct plating method, and agreement between the methods was calculated. Considering results from both internal and independent laboratory trials, overall agreement between the methods was 90%. Chi-square analysis showed, with few exceptions, that results of the Soleris and direct plating methods were not statistically different. Ruggedness testing was performed, and the Soleris method was found to be robust when challenged with marginally suboptimal assay conditions. Results of inclusivity testing showed that the Soleris test vial medium supports the growth of a wide variety of yeasts and molds common to foods. Results of exclusivity testing showed that bacteria do not produce positive results, even when present in the vial in relatively high initial concentrations. The Soleris method produces results in 72 h or less and thus offers considerable time savings in comparison to other commonly used yeast and mold methods.