Some conventional and latent anti-listerial effects of essential oils, herbs, carrot and cabbage in fresh-cut vegetable systems

The anti-listerial effectiveness of selected essential oils (EOs) and shredded fresh herbs (thyme, oregano and rosemary) was examined on a range of modified atmosphere packaged fresh-cut vegetables (lettuce, carrot discs, cabbage and dry coleslaw mix). Anti-listerial effects were in the order: thyme EO > oregano EO > rosemary herb > rosemary EO. While thyme EO demonstrated the best anti-listerial effect, direct application of all the EOs damaged product appearance. Shredded fresh rosemary herb appeared to have a major anti-listerial effect, but shredded fresh thyme and oregano showed no anti-listerial effects. However, fresh rosemary herb was only effective in fresh-cut products when it was stomached with the product prior to microbial analysis. The effectiveness of these antimicrobials varied depending on the product type. Greater anti-listerial effects were recorded on carrot discs and shredded cabbage than on shredded lettuce. Adding shredded carrot to packages enhanced the apparent anti-listerial effects, suggesting a synergistic effect between carrot and rosemary.

► Thyme EO had the greatest anti-listerial effect followed by oregano EO; their fresh herbs had no effect.
► Rosemary EO showed weak anti-listerial effects whereas rosemary herb greatly reduced Listeria populations.
► Rosemary herb was only effective when it was stomached with the product prior to microbial analysis.
► Effectiveness of antimicrobials varied depending on product type, greater effects on carrot and cabbage.
► A synergistic effect was seen between carrot and rosemary.