Antifungal Activity Of The Vapour Phases Of Boldus, Poleo and Clove Essential Oils On Aspergillus Section Flavi Isolated From Stored Peanut

PASSONE, M.A.; GIRARDI, N.S.; FERRAND, C.A.; ETCHEVERRY, M.G.

Mendoza

Congreso; ISM Conference 2011; 2011

The antifungal activity of the vapor phase generated by boldus [Pëumus boldus Mol.], poleo [Lippia turbinata var. integrifolia (Griseb.)] and clove [Syzygium aromaticum L.] essential oils against the growth and aflatoxin accumulation by two A. flavus Link (RCP08270 and RCP08108) and two A. parasiticus Speare (RCP08299 and RCP08300) were evaluated at three water activity (aW) levels. The basic medium used in this study was 2% peanut meal extract agar (PMEA) adjusted to 0.98, 0.95, 0.93 aW by addition of a non-ionic solute glycerol. Effects of EO vapor phases were determined by adding boldus and poleo EOs to sterilized filter paper disc (5 mm) at concentrations of 1000, 1500, 2000, 2500 and 3000 ppm. EO clove was used at concentrations of 1000, 2000, 3000, 4000 and 5000 ppm. Plates were inoculated and incubated for 11 days at 25 °C. Effects of these treatments on lag phase (h), growth rate (mm h-1) and aflatoxin B1 (AFB1) accumulation was evaluated. The behavior of the four isolates was similar; the antifungal effect of the three EO volatile fractions was enhanced by decreasing aW. Boldus EO at doses > 1500 ppm showed the greatest effect on Aspergillus section Flavi, totally inhibiting growth at all aW levels assayed. Poleo EO was able to extend the lag phases of all Aspergillus isolates by 14.8, 18.1 and 136.9 h at 0.98, 0.95 and 0.93 aW, respectively; while clove EO could only increase the lag phase in the order of 3 to 231.8 h at 0.93 aW. The antifungal effect of poleo and clove EOs was highly dependent on aW. The Aspergillus growth rate was reduced by 45.8% in presence of poleo EO at 0.95 aW, while between 60.6 and 100% reduction was observed when aW was further lowered to 0.93. The lowest antifungal effect was observed at 0.98 aW: growth reductions in the order of 16.1-30.4% were obtained with poleo EO treatments. Clove EO did not show homogeneous antifungal activity against Aspergillus section Flavi. At 0.98 aW the inhibitory effect was evident at 5000 ppm; the dose of 4000 ppm showed antifungal effect for only three isolates (RCP08108, RCP08299, RCP08300) and the doses of 1000-3000 ppm stimulated fungal growth. The presence of boldus EO volatile fraction in the surrounding atmosphere of peanut based medium had an important effect on AFB1 accumulation. Boldus EO totally inhibited AFB1 accumulation by A. flavus strains, while poleo EO was less effective (from stimulation to 100% inhibition). At the highest aW levels studied; all Aspergillus strains tended to show AFB1 stimulation in the presence of clove EO. The results obtained in this work clearly indicate that the volatile fraction of boldus EO have potential to be used in the control of aflatoxigenic fungi in stored peanut.