Purpose: It is believed that under stressful conditions, pathogens can enter into the VBNC state. Hence, there is a concern if antimicrobial exposure induces VBNC state in foodborne pathogens. The objective is to determine whether treatments with plant antimicrobials inactivate Salmonella or induce the state of VBNC.
Methods: In vitro, S. Newport culture was exposed to 0.1% of one of the three essential oils or their active components or phosphate buffered saline (PBS) for 0 and 3 h. In addition 10 grams of organic iceberg lettuce samples were inoculated with S. Newport and treated with 200 mL of 0.5% of one of the 3 essential oils or their active components in PBS for 2 min. The samples were stored at 4°C, and survivors enumerated on days 0, 1 and 3. Viability of the treated cells was determined using LIVE/DEAD® staining and viewing under a fluorescence microscope.
Results: In vitro, oregano oil and carvacrol demonstrated inactivation as the cells fluoresced red and no survivors were detected at both time points. Lemongrass oil and citral showed few green cells but exhibited a time-dependent reduction of 2.9-5.2 logs and 3.5-8.5 logs by 3 h, respectively. Cinnamon oil and cinnamaldehyde showed more green than red cells and had about 2.1-5 and 1.8-5 log reductions by 3 h, respectively. On iceberg lettuce, all treatments demonstrated a 2-3 log reduction in Salmonella population on Days 0 and 1 with no survivors detected by Day 3, in comparison to PBS that had survivors. The viability assay indicated corresponding inactivation/viability. The results showed inactivation of Salmonella (no induction of VBNC) by plant antimicrobials.
Significance: The results could provide the organic produce industry with natural sanitizers that are effective in killing Salmonella.