Fresh culinary herbs decontamination with essential oil vapours applied under vacuum conditions

Abstract

Application of essential oils (EOs) in vapour phase under vacuum conditions may increase the effectiveness of EOs to sanitize plant products. Different treatments with EOs vapor were studied in vitro and in vivo against saprophyte microflora and pathogens at laboratory, pilot plant and industrial scales. Vapor of carvacrol combinations with oregano and peppermint essential oils (80:20 v:v) showed the best microbial reductions up to 1.5 log units for mesophiles (in vitro at laboratory scale), 0.9–3.9 log units for several isolated molds (in vitro at pilot plant scale) and approximately 1 log unit for Listeria innocua (in vivo at pilot plant scale). Particularly, carvacrol:oregano and carvacrol:peppermint vapors showed the highest mold log reductions (>3.3) for Botrytis cinerea, Alternaria alternata and Aspergillus niger while Fusarium spp. and Penicillium spp. showed lower reductions. EOs vapors concentrations lower than 0.5 mg L−1 did not achieve mold reductions higher than 0.2 log units while EOs vapors concentrations ≥10 mg L−1 did not increase the antifungal activity. Fresh cilantro treated at industrial scale with vapor of carvacrol:peppermint (less off-flavors than carvacrol:oregano) (80:20 v:v) at 8 mg L−1 under vacuum (adapting a vacuum cooling system) showed 0.8, 1.8 and 1.2 lower mesophiles, psychrophiles and enterobacteria log units, respectively, than untreated samples after 12 d at 2 °C of storage. Yeast and mold growth in cilantro was low throughout the studied period at storage temperature of 2 °C. Yellowing and browning of cilantro treated at 8 mg L−1 was also minimal, compared to the rest of treatments, after 12 d at 2 °C. In conclusion, the application of carvacrol:peppermint (80:20 v:v) vapor at 8 mg L−1 under vacuum in an industrial installation may extend the shelf life of fresh cilantro further than 12 d at 2 °C ensuring its microbial and visual quality.