EVALUATION UNDER COMMERCIAL CONDITIONS OF THE APPLICATION OF CONTINUOUS, LOW CONCENTRATIONS OF OZONE DURING THE COLD STORAGE OF TABLE GRAPES

Abstract

Botrytis cinerea causes gray mold, a postharvest disease of table grapes. The ability of ozone (O3) in air to inhibit gray mold in stored grapes was reported in chamber studies, but O3 needed evaluation under commercial conditions. O3 merits attention because it is pesticide-residue free and allowed as organic by the USDA National Organic Program. Tests were conducted at three commercial facilities using pallets of 'Flame Seedless', ‘Thompson Seedless', and ‘Princess Seedless’ grapes in uncoated, corrugated fiberboard boxes containing grapes in ventilated cluster bags or hard plastic clamshell containers. Grape berries inoculated with B. cinerea were placed within grape clusters at the beginning of storage. After cold storage, the spread of infection, natural incidence of decay, and cluster appearance were evaluated. After initial pre-cooling in air, grapes were stored at -0.5 to 3°C with a day/night cycle of 100 ppb O3 (day) and 300 ppb O3 (night) for 5 to 8 weeks. At each exam, six 9-kg boxes with 9 cluster bags or 4 clamshell containers were examined. The mean number for all tested cultivars of berries adjacent to inoculated berries that became infected by the end of storage was 0.8 in the O3 atmosphere compared to 3.1 among those in air. The mean percentage for all tested cultivars of naturally decayed berries at this time in O3 was 2.4% compared to 5.8% among those in air. Cluster appearance was not harmed and storage life was extended by 2 to 3 weeks by O3. The uncoated, paper fiber corrugated boxes used in these tests reduced O3 diffusion into them more than coated corrugated fiberboard, expanded polystyrene, or corrugated plastic boxes. Selection of packaging that maximizes O3 concentrations within packages should improve control of gray mold.