Impact of Ozonated Water on the Quality and Shelf-life of Fresh Citrus Fruit,Stone Fruit,and Table Grapes

Spores of fungi that cause postharvest decay of fresh fruit die rapidly in ozonated water. We determined the impact of sporocidal or higher O₃ doses on fruit shelf-life and quality. Green mold and sour rot on citrus fruit, caused by Penicillium digitatum and Geotrichum citri-aurantii, respectively, were not reduced by 20 min immersion in 10 ppm O₃. These fungi infect through wounds; their spores were placed in shallow wounds (l mm wide by 2 mm deep) 24 hr before treatment. On five peach varieties, the average natural incidence of brown rot, caused by Monilinia fructicola, was reduced from 10.9 to 5.4% by 1 min immersion in 1.5 ppm O₃. A treatment of 15 min with 5 ppm O₃ further reduced decay to 1.7%, but consistent control of brown rot was associated only with this severe treatment and it caused shallow pits on the fruit. Brown rot caused by spores placed in wounds before treatment was not controlled. Immersion for 1 or 5 min in 5 ppm O₃ reduced natural aerobic bacteria populations by 1.1 and 1.6 log₁₀ units, respectively, and yeast and filamentous fungal populations by 0.7 and 1.3 log₁₀ units, respectively. Spores of Botrytis cinerea, cause of gray mold, were sprayed on table grape clusters, the clusters were dried, and then immersed for 1 to 6 min in 10 ppm O₃. In two tests, immersion for 1 min in O₃ reduced gray mold from 35% among untreated grapes to about 10%, while in two other tests the incidence was only reduced from 35 to 26%. Minor injury to the rachis of grape clusters occurred at high O₃ rates. Immersion in ozonated water did not control postharvest decay of citrus fruit, injured peaches and nectarines at doses that reliably controlled decay, and on table grapes control was irregular and caused minor rachis injury at high rates.