Effect of essential oil from fresh leaves of Ocimum gratissimum L. on mycoflora during storage of peanuts in Benin

Abstract

The aim of this study was to evaluate the effect of essential oil from fresh leaves of Sweet Fennel (Ocimum gratissimum) on mycoflora and Aspergillus section Flavi populations in stored peanuts. Aspergillus, Fusarium and Mucor spp. were the most common genera identified from peanuts at post-harvest in Benin by using a taxonomic schemes primarily based on morphological characters of mycelium and conidia. The isolated fungi include Aspergillus niger, A. parasiticus, A. flavus, A. ochraceus, Fusarium graminearum, F. solani, F. oxysporum and Mucor spp. The most prevalent fungi recorded were A. niger (94.18%), A. flavus (83.72%), A. parasiticus (77.90%), A. ochraceus (72.09%), F. graminearum (59.30%) and F. oxysporum (51.16%). Antifungal assay, performed by the agar medium assay, indicated that essential oil exhibited high antifungal activity against the growth of A. flavus, A. parasiticus, A. ochraceus and F. oxysporium. The minimal inhibitory concentration (MIC) of the essential oil was found to be 7.5μl/ml for A. flavus and A. parasiticus and 5.5μl/ml for A. ochraceus and F. oxysporium. The minimal fungicidal concentration (MFC) was recorded to be 8.0μl/ml for A. flavus and A. parasiticus, 6,5μl/ml for A. ochraceus and 6.0μl/ml for F. oxysporium. The essential oil was found to be strongly fungicidal and inhibitory to aflatoxin production. Chemical analysis by GC/MS of the components of the oil led to the identification of 31 components characterized by myrcene (6.4%), α-thujene (8.2%), p-cymene (17.6%), γ-terpinene (20.0%), and thymol (26.9%) as major components. The essential oil of Sweet Fennel, with fungal growth and mycotoxin inhibitory properties, offers a novel approach to the management of storage, thus opening up the possibility to prevent mold contamination in stored peanuts.