Effect of combination of essential oils and bacteriocins on the efficacy of gamma radiation against Salmonella Typhimurium and Listeria monocytogenes

Purpose : Using essential oils (EO) alone or combined EO with nisin to enhance the lethality of Salmonella Typhimurium and Listeria monocytogenes to gamma-irradiation treatment. Materials and methods : Cell suspension or inoculated carrots (10(6) colony forming unit (CFU)/ml) of L. monocytogenes or Salmonella Typhimurium were treated with carvacrol and mountain savory EO alone or treated by the combined EO plus nisin and were irradiated at different doses. The radiation dose required to reduce bacterial population by 90% (D-10 value) and the relative sensitivity (RS) of treated bacteria to irradiation were calculated. Results : The RS of L. monocytogenes cell suspension to irradiation was increased by 4.19 and 6.31 times when treated by carvacrol plus nisin and mountain savory plus nisin, respectively, as compared to the control. The RS of Salmonella Typhimurium cell suspension to irradiation was increased by 1.84-fold when treated with carvacrol plus nisin. Coated carrots by nisin plus carvacrol increased the RS of L. monocytogenes to irradiation by 2.74 times while coated carrots by nisin and nisin plus carvacrol increased the RS of Salmonella Typhimurium to irradiation by 2.46 and 2.52, respectively. Conclusions : The combined EO with nisin and irradiation could increase the RS of L. monocytogenes and Salmonella Typhimurium.