Purpose: The main goal of this work was to optimize recovery of low numbers of stressed Salmonella in low water activity foods and spices for application with real-time PCR detection method.
Methods: Whole black pepper (25 g), wheat flour (25 g), and dried whole egg (100 g) samples where artificially contaminated with different sublethally stressed Salmonella strains and stabilized for 14 days prior to testing. Actero™ Salmonella Enrichment Media was used, alone (75 mL, black pepper), or supplemented with 50 mg/L green malachite (175 mL, wheat flour), or 5% non-fat dried milk (600 mL, dried whole egg) to optimize recovery of stressed Salmonella in a single enrichment step followed by the detection with the DuPont™ BAX® System Real-Time PCR Assay for Salmonella. For each matrix, 20 low level and five high level inoculum replicates, as well as five control samples, were analyzed according to the alternative protocol to compare to the samples tested by the US FDA BAM 5 or USDA-FSIS MLG 4.08 methods.
Results: As short as 14-18 hours of enrichment were sufficient to detect as low as 0.2-7.1 Salmonella MPN/sample. According to the Probability of Detection, the candidate method showed equivalent performance to the reference methods. No false positive or false negative results were observed. Furthermore, the candidate method applied to 240 low water activity matrix samples, including 25 g portions of ground black pepper, paprika, rye flour, and soy flour, as well as 375 g composite samples of whole black pepper, demonstrated high accuracy and reliability.
Significance: The candidate method showed the sensitivity comparable to the traditional culture-based methods, with a significant reduction in time to result.