Chemical basis of anti-listerial effects of rosemary herb during stomaching with fresh-cut vegetables

- A number of rosemary extracts were examined in vitro and found to be powerful anti-listerial agents.
- Chemical composition of extracts vary depending on extraction method used.
- PCA analysis show that kill level is most highly correlated with verbenone content.
- The effects correlate to increased levels of the herb's most powerful anti-listerial compounds.

Fresh rosemary herb has demonstrated much stronger anti-listerial effects when stomached with contaminated fresh-cut vegetables than those obtained by application of rosemary essential oils. Various types of rosemary extracts (hydrodistillates, CO2 extracts, hexane/acetone extracts) were analysed by GC-MS and tested for anti-listerial effects in vitro. Principal component analysis showed that verbenone levels were most correlated with anti-listerial effects, followed by levels of camphor. Stomaching rosemary herb greatly increased headspace levels of verbenone and camphor (by up to 20 times) compared to intact or chopped fresh rosemary. It is speculated that by crushing the herb under water, stomaching released enhanced levels of these components as lipophilic nanosomes which rapidly migrated to lipophilic surfaces, including the membranes of Listeria cells.