Investigations On The Essential Oils Of Boldus, Poleo, Clove, Anise And Thymus For Its Potential Use As Antifungal Agents Against Aspergillus Section Nigri

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

Mendoza

Congreso; ISM Conference 2011; 2011

This study was carried out to determine the efficacy of five plant-derived essential oils (EOs) (boldus [Pëumus boldus Mol.], poleo [Lippia turbinata var. integrifolia (Griseb.)], clove [Syzygium aromaticum L.], anise [Pimpinella anisum] and thymus [Thymus vulgaris]) under different water activity (aW) regimes on Aspergillus section Nigri strains isolated from stored peanut. Effects of EOs added to peanut meal extract agar (PMEA) at concentrations of 500, 1500 and 2500 ppm on three A. niger aggregate (RCP176, RCP42, RCP191) and three A. carbonarius (RCPG, RCP4, RCP203) were evaluated. Peanut meal extract agar (PMEA) was prepared at 2%. The aW of the medium was adjusted to 0.98, 0.95 and 0.93. Plates were inoculated and incubated for 14 days at 25 °C. Lag phase (h) and radial growth rate (mm h-1) were calculated. In control treatments, mean lag phase increased from 37.7 to 61.2 h and from 44.3 to 102.8 h when the water availability ranged from optimal to marginal conditions (0.98 to 0.93 aW) for both A. niger aggregate (RCP42, RCP176, RCP191) and A. carbonarius (RCPG, RCP4, RCP203). At 1500 and 2500 ppm of boldus, poleo and clove EOs the strains were not able to reach the exponential phase at all aW conditions. The lag phase of all species tested was significantly increased (p<0.001) for 500 ppm of boldus, poleo and clove, regardless of water conditions assayed. Aspergillus niger aggregate strains showed an increase in their lag phase between 13.9 and 175.6 h, 11.8 and 106.9 h and 65.8 and 144.7 h when grown with 500 ppm of boldus, poleo and clove respectively, regardless of the aW. Aspergillus carbonarius strains appear to be more sensible to these treatments (500 ppm of boldus, poleo and clove EOs) with increases in lag phases estimated between 24 and >300 h. In general reductions of Aspergillus section Nigri lag phases were observed with the addition of anise (500 and 1500 ppm) and thyme (500 ppm) to peanut medium modified at 0.98 aW. The profiles of growth rates showed, that poleo and clove EOs, at the lowest concentration used (500 ppm) significantly reduced (p < 0.001) the growth rate of the fungal isolates. The sensitivity of A. carbonarius isolates to 500 ppm of boldus EO was demonstrated; however this inhibitory effect was not reflected at the A. niger aggregate strains growth level. Results obtained in the present study indicate the possibility of exploiting boldus, poleo and clove EOs in the control against strains of Aspergillus section Nigri responsible for biodeterioration of stored food products.