A range of fungal species are associated with postharvest spoilage of grapes. However, Aspergillus carbonarius is the primary fungus responsible for the contamination of grapes with ochratoxin A, a mycotoxin causing several confirmed negative health effects in humans and animals. Aiming to find a method, safe for consumers, to prevent postharvest decay and ochratoxin A contamination of grapes, the potential use of essential oils as preservatives was investigated. Essential oils of Origanum dictamnus (dittany), Origanum onites (oregano), Origanum microphyllum (marjoram), Thymbra capitata (thyme), Satureja thymbra (savory), Rosmarinus officinalis (rosemary), Laurus nobilis (laurel), and Salvia officinalis (sage) were tested. The essential oil components were identified by gas chromatography–mass spectrometry analysis. A first evaluation of the effectiveness of essential oils was performed in vitro at a range of concentrations up to 300 μL L−1. Based on the results of the in vitro tests, the four most effective essential oils (O. dictamnus, O. onites, T. capitata, and S. thymbra) were tested on Sultana grapes during postharvest storage. The four essential oils tested, which had carvacrol and/or thymol as a common component, at a high concentration significantly reduced or even inhibited growth of the fungus in all treatments. As revealed from the results, the essential oils of O. dictamnus, O. onites, and S. thymbra were the most effective, causing total inhibition of the growth of the fungus with a minimum concentration of 100 μL L−1, followed by the essential oil of T. capitata, which showed total effectiveness with a minimum concentration of 200 μL L−1. Although essential oils of O. microphyllum, L. nobilis, S. officinalis, and R. officinalis had a significant effect on the growth of A. carbonarius, they failed to inhibit its growth at any of the concentrations tested.

  • Dittany, oregano, thyme, and savory EOs were most effective against A. carbonarius.

  • The most effective EOs had carvacrol or thymol as their predominant component.

  • A phytotoxic effect was observed in the grapes near the source of the EOs.

  • EOs use can limit the growth of A. carbonarius on grapes during postharvest storage.

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