Efficacy of oregano oil in the inactivation of Salmonella typhimurium on lettuce

This study was conducted to determine the efficacy of oregano oil in the inactivation of Salmonella typhimurium inoculated onto iceberg lettuce. The effect of washing with oregano oil (Oreganum onites), typical of Turkey, at three different concentrations (25, 40 and 75 ppm) and four different treatment times (5, 10, 15 and 20 min) on survival of S. typhimurium inoculated to fresh cut iceberg lettuce were determined at 20 °C and compared with a 50 ppm chlorine wash at the same conditions. The spot and dip inoculation methods for applying inoculum to iceberg and romaine type lettuce were evaluated and the effects of selective and nonselective media on the recovery of S. typhimurium were also examined. Populations of S. typhimurium recovered from spot and dip inoculated lettuce were not significantly different (p > 0.05). No significant differences were found between two different media, and two different lettuce types (p > 0.05). Reductions of S. typhimurium by washing with oregano did not exceed 1.92 logarithmic units regardless of the washing times and concentrations. The effectiveness of washing lettuce with 75 ppm oregano oil on inactivation of S. typhimurium was comparable with that affected by 50 ppm chlorine. The results suggested that oregano oil might be a suitable decontamination alternative to chlorine for lettuce.