In Vitro Evaluation Of Five Essential Oils As Botanical Fungitoxicants Against Aspergillus Section Flavi For The Stored Peanut Protection

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

Mendoza

Congreso; ISM Conference 2011; 2011

The antifungal potential 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]) was evaluated against aflatoxigenic Aspergillus strains on peanut based medium conditioned at different water activity (aW) levels. Effects of EOs added to peanut meal extract agar at concentrations of 500, 1500 and 2500 ppm on lag phase, growth rate and aflatoxin B1 (AFB1) accumulation by two A.flavus Link (RCP08270 and RCP08108) and two A. parasiticus Speare (RCP08299 and RCP08300) were evaluated at three aW levels (0.98, 0.95, 0.93). The five EOs analyzed have been shown to influence lag phase and growth rate. Statistical analyses showed that their efficacy depended mainly on the substrate aW levels, type of EO assayed and the EO concentrations. In untreated controls lag phases ranged from 28.7 to 50.7 h for all strains at 0.98 aW. However, mean lag phase increased (71.0 - 75.3 h) at 0.93 aW. The mean lag phase at 0.98 aW increased by 112.8, 234.9 and >300 h with 1500 ppm of boldus, poleo and clove, respectively. Changes in aW alone reduced growth rate by 9 ? 53 % between 0.98 and 0.93 aW. Anise and thyme (1500 ppm) reduced growth rate between 16 and 71, 19 and 86 and 100 % at 0.98, 0.95 and 0.93, respectively. Likewise, all EOs showed significant impact on AFB1 accumulation. This effect was closely dependent of the Aspergillus section Flavi isolates, EO concentrations and aW. The antiaflatoxigenic property of boldus and poleo EOs (500 ppm) was more marked with the medium aW reduction; inhibition percentages were estimated at 75, 83 and 100% at 0.98, 0.95 and 0.93 aW, respectively. Although the low dose (500 ppm) of boldus, poleo and clove showed no significant effects on lag phase (range of increase = 0 - 75 %), growth rate (range of reduction = 0 - 65 %) and AFB1 (range of reduction = 27 - 100%), the application of high concentrations of these EOs (2500 ppm for boldus and poleo and 1500 ppm for clove) completely inhibited growth and AFB1 accumulation by Aspergillus species, regardless of medium aqueous availability. These findings support the application of boldus, poleo and clove EOs for surface treatment and leaves open de possibility of using them as vapor exposure to prevent mold contamination in stored peanut.