The results confirmed the antimicrobial activity of the aromatic herbs, and the anti-listerial effects resulted in the order: thyme EO > oregano EO > rosemary herb > rosemary EO (Table 1).
Table 1. - Summary of the overall maximum reduction in counts for all the antimicrobial treatments tested on lettuce, carrot discs, coleslaw mix and shredded cabbage at 8°C (TBCs=total bacterial counts, ND=not determined) Click here to enlarge.
Thyme EO resulted the most effective against Listeria, however the direct application of all tested essential oils damaged the appearance of fresh-cut product. In general, it is not possible the direct use of essential oils during minimally processing because of their phytotoxic effects on vegetable.
Shredded fresh rosemary showed an high potential anti-listerial effect, while shredded fresh thyme and oregano did not show anti-listerial effects. However, fresh rosemary herb resulted effective only when it was stomached with fresh-cut vegetable prior to microbial analysis.
The effectiveness of these antimicrobial treatments varied according to the fresh-cut product: the best antimicrobial effects were detected on carrot discs and shredded cabbage. The same scientists have hypothesized a sinergistic antimicrobial effect between carrot and rosemary and cabbage and rosemary.
Source: Scollard J., Francis G.A., O'Beirne D., "Some conventional and latent anti-listerial effects of essential oils, herbs, carrot and cabbage in fresh-cut vegetable systems", 2013, Postharvest Biology and Technology, Volume 77, pagg. 87-93. Further info: www.sciencedirect.com/science/article/pii/S0925521412002657