Location: Commodity Protection and Quality
Title: Evaluation under commercial conditions of the application of continuous, low concentrations of ozone during the cold storage of table grapes Authors
Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2012
Publication Date: December 1, 2012
Citation: Smilanick, J.L., Mlikota Gabler, F., Margosan, D.A. 2012. Evaluation under commercial conditions of the application of continuous, low concentrations of ozone during the cold storage of table grapes. Acta Horticulturae. 945:357-361. Interpretive Summary: Table grapes will rot after harvest unless actions are taken to stop this from happening. Currently, grapes are treated commercially with sulfur dioxide gas to stop the rot, but this process can bleach the color from some of the berries and this treatment is banned from use on grapes produced in compliance with the USDA National Organic Program (NOP) rules. As an NOP acceptable alternative to sulfur dioxide, we applied constant low concentrations of ozone gas within cold rooms where grapes are stored and found it can significantly control rot.
Technical 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. Ozone 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’, ‘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. At 2-week intervals, 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 parts per billion (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 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 percentage of naturally decayed berries at the end of storage 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, corrugated fiberboard boxes used in these tests impeded O3 penetration more than coated corrugated fiberboard, expanded polystyrene, or corrugated plastic boxes. Selection of packaging that maximizes O3 penetration should improve control of gray mold. A color-change dosimeter, originally intended for safety purposes, can be used to estimate O3 penetration into boxes.