Evaluation of the efficiency of allspice, thyme and rosemary essential oils on two foodborne pathogens in in-vitro and on alfalfa seeds, and their effect on sensory characteristics of the sprouts.

Seeds are usual source of contamination and their sprouts are commonly associated foodborne illness. Therefore, the aim of this study was to evaluate the antibacterial vapor phase efficiency of allspice, thyme and rosemary essential oils on two foodborne pathogens in in vitro and on alfalfa seeds, including the chemical profile of the tested EOs and their effect on the sensory characteristics of the sprouts. Antibacterial activity was determined through the minimal inhibitory concentration (MIC) of EOs in vapor phase to inhibit the growth of Listeria monocytogenes and Salmonella Typhimurium in culture media and on alfalfa seeds. Also, the germination and the effect on sensory characteristics of the sprouts were determined. Thyme EO was the most effective of the tested EOs on culture media and on alfalfa seeds, against both bacteria. When rosemary EO was tested against L. monocytogenes in alfalfa seeds, the MIC (4.0 mL/Lair) was higher, compared to the one obtained in culture media (2.7 mL/Lair). But when this EO was tested against S. Typhimurium, the MIC in alfalfa seeds was lower than in culture media (11.7 vs 13.3 mL/Lair). Allspice EO resulted more effective against both bacteria in alfalfa seeds (6.0 mL/Lair for L. monocytogenes and 6.7 mL/Lair for S. Typhimurium), compared to culture media (12.0 mL/Lair for L. monocytogenes and 13.3 mL/Lair for S. Typhimurium). Vapor phase EOs MICs resulted in significant (p ≤ 0.05) decreases of L. monocytogenes and S. Typhimurium counts compared to the control. There also was a significant (p ≤ 0.05) difference between systems (in vitro or on alfalfa seeds) despite the microorganism or the evaluated EO. Treatment alfalfa seed with vapor phase EOs, did not affect the seed germination. Sensory acceptability of the sprouts, obtained of treated seeds, did not were significant (p ≥ 0.05) different of the sprouts obtained from the non-treated seeds.

Lorenzo-Leal AC ，Palou E ，López-Malo A 《-》

Antimicrobial activities of gaseous essential oils against Listeria monocytogenes on a laboratory medium and radish sprouts.

The aim of this study was to evaluate the antimicrobial activities of gaseous essential oils (EO gases) against Listeria monocytogenes on the surfaces of a laboratory medium and radish sprouts. We determined the minimal inhibitory concentration (MIC) and minimal lethal concentration (MLC) values of EO gases from eight EOs extracted from basil leaves, carrot seed, cinnamon bark, cinnamon leaves, clove flower buds, oregano leaves, thyme flowers (linalool), and thyme leaves (thymol) against L. monocytogenes on a nutrient agar supplemented with 1% glucose and 0.025% bromocresol purple (NGBA). Oregano, thyme thymol, and cinnamon bark EO gases showed the strongest antilisterial activities (MIC and MLC, 78.1μL/L). We also investigated the inhibitory and lethal activities of these gases against L. monocytogenes on the surface of radish sprouts. The number of L. monocytogenes after exposure to EO gases at ≥156μL/L was significantly (P≤0.05) lower than that of untreated L. monocytogenes. For example, the initial number of L. monocytogenes on the surface of radish sprouts (ca. 6.3logCFU/g) decreased by 1.4logCFU/g within 24h at 30°C and 43% relative humidity (RH) without EO gas treatment, whereas the number of L. monocytogenes after exposure to oregano, thyme thymol, and cinnamon bark EO gases at 156μL/L decreased by 2.1, 2.1, and 1.8logCFU/g, respectively, after 24h. Although EO gases exerted greater lethal activities at higher concentrations (312 and 625μL/L), L. monocytogenes on the surface of radish sprouts was not completely inactivated. The number of L. monocytogenes on sprouts treated with oregano, thyme thymol, and cinnamon bark EO gases at 625μL/L decreased by 2.7-3.0logCFU/g after 24h at 30°C and 43% RH. Results indicate that EO gases that showed antilisterial activities on a laboratory medium also exhibited reduced lethal activity on the surface of radish sprouts. These findings will be useful when developing strategies to inactivate L. monocytogenes and possibly other foodborne pathogens on sprouts and perhaps other foods using EO gases.

Lee G ，Kim Y ，Kim H ，Beuchat LR ，Ryu JH ... -  《-》

Essential oils of thyme and Rosemary in the control of Listeria monocytogenes in raw beef.

de Oliveira MM ，Brugnera DF ，Piccoli RH 《-》

Synergistic activities of gaseous oregano and thyme thymol essential oils against Listeria monocytogenes on surfaces of a laboratory medium and radish sprouts.

We investigated combinations of gaseous essential oils (EO gases) for their synergistic inhibitory activities against Listeria monocytogenes on a laboratory medium and radish sprouts. The minimum inhibitory concentrations and minimum lethal concentrations of oregano, thyme thymol, and cinnamon bark EO gases against L. monocytogenes were 0.0781 μL/mL on nutrient agar supplemented with glucose and bromocresol purple (NGBA). A checkerboard assay showed that combinations of oregano and thyme thymol EO gases and of oregano and cinnamon bark EO gases exert the strongest synergistic antilisterial activity (fractional inhibitory concentration index [FICI] = 0.3750). A combination of thyme thymol and cinnamon bark EO gases also had a synergistic effect (FICI = 0.5000) on L. monocytogenes on NGBA. Combinations of oregano and thyme thymol EO gases were tested for synergistic antimicrobial activity against L. monocytogenes on radish sprouts. A combination of these gases, each at 0.313 μL/mL, caused a significant (P ≤ 0.05) reduction in the number of L. monocytogenes on radish sprouts compared with reductions caused by treatment with oregano or thyme thymol EO gas alone at the same concentration. Our findings provide information that will be useful when developing antimicrobial applications using EO gases to control L. monocytogenes in the food industry.

Cho Y ，Kim H ，Beuchat LR ，Ryu JH ... -  《-》

Antibacterial activity of Rosmarinus officinalis L. and Thymus vulgaris L. essential oils and their combination against food-borne pathogens and spoilage bacteria in ready-to-eat vegetables.

Iseppi R ，Sabia C ，de Niederhäusern S ，Pellati F ，Benvenuti S ，Tardugno R ，Bondi M ，Messi P ... -  《-》