Antimicrobial effects of different combined non-thermal treatments against Listeria monocytogenes in broccoli florets

• Four nanoemulsion of essential oils (EO) were incorporated in chitosan based coatings.
• Modified chitosan based coating of mandarin EO showed highest antilisterial activity.
• Ozonated water, UV-C, γ-irradiation were used in combined treatments with coating.
• Coating plus γ-irradiation was the best combined treatment during broccoli storage.

The antilisterial effect of three non-thermal treatments in combination with a bioactive coating formulation on broccoli florets inoculated with Listeria monocytogenes was evaluated. The nanoemulsions of carvacrol, bergamot, lemon and mandarin essential oils (EO) were incorporated in native and modified chitosan coating formulations and the antilisterial effect in inoculated samples was evaluated. The modified chitosan based coating containing mandarin EO was the best treatment which caused a load reduction of 1.46 log CFU/g after 6 days of storage. The antilisterial effects of this coating formulation in combination with ozonated water, UV-C and γ-ray treatments on inoculated samples were evaluated during 13 days storage at 4 °C. The combined coating and ozonated water showed very high antilisterial effects at days 1 and 3; however, their antilisterial activity was reduced after day 5. The combined coating and UV-C did not show any additive effect against L. monocytogenes as compared to coating alone. The best antilisterial activity was obtained in the combined coating and γ-rays. This combined treatment caused an increase in relative radiation sensitivity of L. monocytogenes by 1.33-fold. Further, this combined treatment ensured microbial safety during storage with a reduction of L. monocytogenes by 2.5 log CFU/g after 13 days.