Effects of several environmental factors on the anti-Listeria monocytogenes activity of an essential oil of Picea excelsa

The effects of several environmental factors on the anti-Listeria monocytogenes activity of an essential oil of Picea excelsa were explored by determination of active concentrations using two methods and with survival curves. In trial conditions, the serovars 1/2c and 4b behaved similarly. A dose of 0.2-0.3% (v/v) of essential oil was bactericidal for 10(5) - 10(7) cells contained in 1 ml of Tryptone Soy Broth Yeast Extract at pH 6 and 7 incubated at 13 and 37 degreesC and of medium supplemented with levan. Introduction of sodium caseinate, agar or fat into the test medium and use of a cheese medium decreased the bactericidal effects of the essential oil. Basic pH, addition of NaCl or use of Tryptone Soy Broth and saline solution increased its antilisterial activity. Serovar 1/2c survival curves exhibited an exponential death rate followed by a tailing effect in the presence of the minimal bactericidal concentration of the essential oil. A three log(10) reduction of cell viability was obtained within 100 min in Tryptone Soy Broth Yeast Extract, within longer exposure in media supplemented with NaCl or at basic pH. (C) 2003 Elsevier B.V. All rights reserved.