Inhibition of Listeria monocytogenes by exposure to a combination of nisin and cold-pressed terpeneless Valencia oil

Listeria monocytogenes is an important foodborne pathogen and its control in foods is a significant challenge. This study evaluated the effectiveness of nisin and cold-pressed terpeneless Valencia oil (CPTVO) on limiting L. monocytogenes growth. Disk diffusion assays were performed to determine the effects of CPTVO and nisin individually and in combination. Together, these antimicrobials produced a zone of inhibition that was significantly larger (P < 0.05) than zones correlating to CPTVO or nisin individually. Furthermore, L. monocytogenesΔsigB had an increased sensitivity to the combination treatment. Growth experiments performed in brain heart infusion (BHI) broth revealed the effects of nisin and CPTVO, individually and in combination on L. monocytogenes growth rate. When L. monocytogenes was grown in BHI containing 0.025% CPTVO and 26 IU/mL nisin, no growth inhibition was observed relative to the control. However, exposure to CPTVO at 0 h followed by the introduction of nisin at 15 h resulted in a statistically significant (P < 0.05) reduction in growth. This approach to inhibiting L. monocytogenes has potential as an all-natural, generally-recognized-as-safe multiple hurdle intervention that may be applicable for ready-to-eat products in which L. monocytogenes is likely to cause foodborne illness.