Combined washing effect of noni extract and oregano essential oil on the decontamination of Listeria monocytogenes on romaine lettuce

NE/OE combined washing treatment effectively reduced the number of Listeria monocytogenes inoculated on romaine lettuce, resulting in more than 1.44‐log reduction compared to sodium hypochlorite washing. The combined washing treatment can be a potential alternative to chlorine‐based sanitizer such as sodium hypochlorite. Summary Combined washing effect of noni extract (NE) and oregano essential oil (OE) on the decontamination of Listeria monocytogenes on romaine lettuce was examined. The fractional inhibitory concentration index (FICI) between NE and three different essential oils (cinnamon leaf, thyme and OE) was determined. Fractional inhibitory concentration index results indicated that OE only had an additive effect (FICI = 1). Noni extract/oregano essential oil combined washing resulted in the greatest reduction in viable cell numbers (3.42 log CFU g−1) relative to non‐washed samples. Furthermore, the combined washing was more effective than sodium hypochlorite washing in terms of reducing the microbial load (>1.44‐log reduction). Washing treatment did not change the surface colour or total phenolic content in lettuce samples. These results suggest that NE/OE combined washing is applicable as a novel decontamination treatment to ensure the microbial safety of romaine lettuce without changing the quality.