Exposure to volatiles of essential oils alone or under hypobaric treatment to control postharvest gray mold of table grapes

Abstract

After harvest, table grapes can easily undergo fungal spoilage, which is mainly caused by Botrytis cinerea, the causal agent of gray mold. To reduce such losses, table grapes are usually treated with conventional fungicides during the season, and cold stored in the presence of sulfur dioxide. However, these applications are not permitted in organic agriculture, and at the same time, there is a growing demand from consumers for fresh fruit free from pesticide residues. The application of essential oils and hypobaric treatments are promising alternatives to sulfur dioxide with minimal environmental impacts and limited concerns about human health risks. The aim of this study was to determine the effectiveness for control of postharvest gray mold of table grapes of 24-h exposure to volatiles of essential oils of Rosmarinus officinalis (rosemary), Mentha piperita (peppermint), and Thymus vulgaris (thyme) individually and in combinations with hypobaric treatment at 50kPa (0.5atm). Exposure to volatiles of rosemary essential oils under atmospheric pressure and hypobaric conditions reduced by around 65% the incidence and McKinney’s Index of gray mold for table grapes that were then stored at room temperature for 9 d and 5 d, respectively, or that were stored at 4°C for 7 d and followed by 3 d shelf life at 20°C. Peppermint essential oils similarly controlled gray mold for grapes stored at room temperature and under hypobaric conditions for 24h. Panel tasting revealed perception of the essential oils soon after the treatments and 24h later for grape berries exposed to vapors of rosemary, peppermint, and Lavandula×ibrida (lavender). Then 48h after treatment, the rosemary and peppermint essential oils were no longer perceived on grapes stored at 4°C and at 20°C. Exposure to volatiles of the rosemary and peppermint essential oils alone or in combination with hypobaric treatment might represent an innovative method to control postharvest gray mold of table grapes, although at least 48h were needed between exposure to volatiles of essential oils and presentation to consumers.