Evaluation of the control ability of five essential oils against Aspergillus section Nigri growth and ochratoxin A accumulation in peanut meal extract agar conditioned al different water activity levels

PASSONE, M. A., GIRARDI, N. S., ETCHEVERRY, M

Congreso; WMF meets IUPAC 2012; 2012

Argentina is subject to climate conditions favorable for the production of a wide range of agricultural products. Peanut exportation increased 0.55 million tons consolidating Argentina as the first worldwide exporter. The contamination of different agricultural commodities with ochratoxin A (OTA) occurs predominantly postharvest. Aspergillus niger aggregate and A. carbonarius are among the major storage fungi found regularly in peanuts stored throughout the world. Therefore, there has been increased interest in the research in using natural antimicrobial or antifungal substances, which may replace synthetic pesticides or contribute to the development of new pest control agents. Essential oils (EOs) from boldo [Pëumus boldus Mol.], poleo [Lippia turbinata var. integrifolia (Griseb.)], clove [Syzygium aromaticum L.], anise [Pimpinella anisum] and thyme [Thymus vulgaris] obtained by hydrodistillation were evaluated for their effectiveness against the growth of A. niger aggregate and A. carbonarius and accumulation of OTA. The evaluation was performed by compound dissolution at the doses of 0, 500, 1500 and 2500 µL/L in peanut meal extract agar (PMEA) and exposure to volatiles of boldo, poleo (0, 1000, 2000 and 3000 µL/L) and clove oils (0, 1000, 3000 and 5000 µL/L), taking into account the levels of medium water activity (0.98, 0.95, 0.93 aW). Statistical analyses on growth of Aspergillus strains indicated that the major effect was produced by oil concentrations followed by substrate aW, and that reductions in antifungal efficiency of the oils tested were observed in vapor exposure assay. At all aW levels, complete fungal growth inhibition was achieved with boldo EO at doses of 1500 and 2000 µL/L by contact and volatile assays, respectively. Contact exposure by poleo and clove EOs showed total fungal inhibition at the middle level tested of 1500 µL/L, regardless of aW, while their antifungal effects in headspace volatile assay were closely dependent on medium aW. The fumigant activity of poleo (2000 µL/L) and clove oils (3000 µL/L) caused growth rate inhibitions by 66.0 % and 80.6 % at 0.98 and 0.93 aW, respectively. The antiochratoxigenic property of the volatile fractions of boldo, poleo and clove EOs (1000 µL/L) was more significant at low aW levels, inhibition percentages were estimated at 14.7, 41.7 and 78.5% at 0.98, 0.95 and 0.93 aW, respectively. Our results suggest that boldo, poleo and clove oils had metabolic effects on OTA biosynthesis pathway of both Aspergillus species. This finding leaves open the possibility to use them as effective non-toxic biopreservatives by vapor exposure in stored peanuts against OTA contamination.