Growth Potential of Listeria monocytogenes in Vegan Salami

The increasing demand for plant-based products has raised concerns regarding the potential presence and growth of Listeria monocytogenes in ready-to-eat products such as plant-based deli slices. In this study, a challenge test was performed to evaluate the growth potential of L. monocytogenes in a vegan salami product. This particular product not only exhibited the highest pH value among the eight similar products available in the supermarket but also had a water activity of 0.96. Additionally, the vegan salami contained no chemical additives with antimicrobial activity, thus possibly representing a "worst case" product for enabling bacterial growth. The product samples were inoculated with two strains of L. monocytogenes and stored at 8 °C during their remaining shelf-life (approximately 30 days). The concentration of L. monocytogenes was measured at the beginning of the test, at three intermediate time points throughout, and at the end. Water activity and pH were also assessed during the challenge test, and noninoculated samples were analyzed for total bacterial counts (TBCs) and screened for the most prevalent bacterial species with MALDI-TOF-MS. A growth potential (δ) of 4.4 log₁₀ cfu/g was observed for the vegan salami, i.e. L. monocytogenes levels increasing from an initial inoculation level of approximately 2.4 log₁₀ to a maximum of 6.8 log₁₀ cfu/g during the challenge test. The screening investigation revealed that species of the genera Carnobacterium and Leuconostoc were the most prevalent. To summarize, the findings from this study demonstrate that there are currently plant-based deli slices on the market that possess the potential to support the growth of L. monocytogenes.