ANTIFUNGAL PROPERTIES OF OLIVE LEAF EXTRACTS AND THEIR PHENOLIC COMPOUNDS

Olive (Olea europaea L.) leaf extracts were obtained using water or different organic solvents such as acetone, methanol and ethyl acetate. Antimicrobial activities of the extracts and some phenolic components were investigated to screen against 30 fungal strains (Alternaria alternata, Aspergillus chevalieri, A. chrysogenum, A. elegans, A. flavus [three strains], A. fumigatus, A. nidulans, A. niger [two strains], A. oryzae, A. parasiticus[four strains], A. tamari, P. verrucosum, A. versicolor, A. wentii, Fusarium oxysporum, F. semitectum, Mucor racemosus, Neurospora crassa, Penicillium citrinum, P. echinulatum, P. griseofulvum, P. italicum, P. roqueforti and Rhizopus oligosporus) using the disc diffusion method. In this study, in terms of inhibition activity, it was determined that aqueous extract was the best as it completely inhibited the growth of 10 molds, followed by acetone and methanol extracts, which were effective against eight molds, and diethyl ether extract, which was effective against 7 out of 30 test fungi. The inhibition zones ranged from 7 to 21 mm. Comparing the sensitivity of the fungi with all crude olive leaf extracts and pure phenolic compounds, we found that A. parasiticus(4) was the most resistant strain while A. wentii was the most sensitive. PRACTICAL APPLICATIONS Foodborne diseases are still a major problem in the world, even in well-developed countries. Fusarium spp., Aspergillus spp., Rhizopus spp. and Penicillium spp. have been reported as the causal agents of foodborne diseases and food spoilage. Raw and processed foods are open to contamination during the production, sale and distribution. Thus, at present, it is a necessity to the food industry to use chemical preservatives to prevent the growth of fungi in foods. Because of the economic impact of spoiled foods and consumer concerns over the safety of foods containing synthetic chemicals, considerable attention has been paid to naturally derived compounds or natural products. Recently, there has been considerable interest in using extracts from plants with antimicrobial activities to control pathogens or toxin-producing microorganisms in foods. Olive leaves have been shown to inhibit or delay the rate of growth of a range of fungi; thus, they might be useful as natural preservatives.