Optimization of Salmonella Detection in Garlic Granules Using Neutralizer-Aided Enrichment and PMAxx-qPCR

Spices with low water activity (a_w) often contain antibacterial substances that complicate the detection of Salmonella using traditional culture methods. These substances can drive Salmonella into a viable but nonculturable (VBNC) state, rendering it undetectable with culture-based methods. This study aimed to enhance the broth for enriching Salmonella in garlic granules by mitigating the inhibitory effects of antibacterial substances. This study optimized the enrichment broth by using 3× buffered peptone water to increase the buffering capacity of the medium, adding magnesium sulfate and sodium pyruvate to promote the self-repair and recovery of bacteria, and adding DL-dithiothreitol (DTT) and corn oil to neutralize the antimicrobial substances in garlic. Garlic granules were artificially contaminated with Salmonella and subjected to a 2-week desiccation process to simulate low a_w conditions during food storage. The results showed that adding DTT and corn oil as neutralizers in the modified buffered peptone water (mBPW) broth significantly enhanced the detection capability of Salmonella in garlic granules, enabling detection of Salmonella at initial contamination levels as low as 5 CFU/g. In contrast, Salmonella was undetectable without the addition of neutralizers during enrichment. In addition, the optimized mBPW broth was tested on spices other than garlic granules, demonstrating its effectiveness (without neutralizers) in detecting Salmonella in star anise and black pepper. Notably, this study demonstrated that the combination of neutralizer-aided enrichment and PMAxx-qPCR successfully enabled the detection of viable Salmonella in garlic granules. The entire process can be completed in approximately 26 h, demonstrating the method's swiftness and effectiveness in detecting viable cells. This approach provides a fast and sensitive method for the detection of Salmonella in garlic granules, with promising potential for application in similar inhibitory food matrices.