Volume 59, January 2016, Pages 468–477
Highlights
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- Oregano and rosemary essential oils were tested as sanitizers in fresh vegetables.
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- Oregano and rosemary essential oils were tested in mixtures of subinhibitory amounts.
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- Oregano and rosemary essential oils were found to have a synergistic interaction.
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- Combining these essential oils sharply reduced pathogenic bacteria in leafy vegetables.
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- Combining these essential oils sharply reduced native spoilage flora in leafy vegetables.
Abstract
This study assessed the effect of the combined application of essential oils (EOs) from Origanum vulgare L. – oregano (OVEO) and Rosmarinus officinalis
L. – rosemary (ROEO), alone or in combination at subinhibitory
concentrations, against three pathogenic bacteria that are associated
with fresh leafy vegetables: Listeria monocytogenes (L. monocytogenes), Escherichia coli (E. coli) and Salmonella enterica Serovar Enteritidis (S.
Enteritidis). The inhibitory effects were evaluated by determining the
minimum inhibitory concentration (MIC) and the fractional inhibitory
concentration index (FICI) and assessing the viable cell counts in
vegetable broth and artificially infected vegetables over time. Still,
the effects of the EOs on native spoilage native flora were assessed.
The MIC of OVEO was 0.6 μL/mL against the test strains either in single
and mixed inoculum. The MIC of ROEO was 5 μL/mL against L. monocytogenes and E. coli and 10 μL/mL against S.
Enteritidis in single inocula, whereas it was 10 μL/mL against the
mixed inoculum. The FICI of the combined EOs was 0.5 against the mixed
bacterial inoculum, which suggested a synergic interaction. The
incorporation of OVEO and ROEO alone (MIC) or combined at different
subinhibitory concentrations in vegetable broth resulted in a decrease
in the viable cell counts of all test strains over 24 h. Similarly, the
EOs alone or in the tested combinations reduced the viable cell counts
of all test strains in experimentally infected fresh vegetables, besides
to decrease the counts of spoiling native flora (mesophilic bacteria,
enterobacteria and fungi). These findings reinforce the rational for the
use of OVEO and ROEO in combination at subinhibitory concentrations to
guarantee the safety and extend the shelf life of fresh vegetables.
Keywords
- Ready-to-eat vegetables;
- Essential oils;
- Enhancing effect;
- Mixed bacterial population
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