Effect of a continuous low ozone exposure (50 nL L−1) on decay and quality of stored carrots

Fresh carrots were treated with or without a continuous atmosphere of 50 ± 10 nL L−1 ozone during storage for up to 6 months at 0.5 °C and >95% relative humidity to determine the effect on decay caused by Sclerotinia sclerotiorum and Botrytis cinerea and quality attributes. Lesions on carrots inoculated with S. sclerotiorum at the beginning of the storage period were reduced in length but the subsequent rate of lesion expansion over time was similar for both treatments. Lesion size and rate of expansion on carrots inoculated with B. cinerea were reduced by ozone. Aerial mycelium of both pathogens was markedly reduced in the ozone treatment, but sporulation of B. cinerea was stimulated, characterized by dense mats of short conidiophores on the lesions. Susceptibility to S. sclerotiorum increased with storage time while susceptibility to B. cinerea peaked at 4 months and then decreased possibly related to carrot moisture loss. The incidence of carrots harboring visible saprophytic mold on the crown was substantially reduced in the ozone treatment. Ozone-induced injury, appearing as blotches of brownish discolored periderm, was slight, but increased with time whereas carrots in the control treatment did not become discolored. Ozone treatment had no effect on fresh weight loss, sprouting of carrot crowns, nor on concentrations of glucose, fructose, sucrose or galactose. Levels of isocoumarin (3-methyl-6-methoxy-8-hydroxy-3,4-dihydroisocoumarin) were slightly elevated and averaged 17.8 mg kg−1 compared with 12.1 mg kg−1 in the controls and may have been associated with reduced lesion growth by B. cinerea. The ozone treatment may be useful for reducing nesting caused by S. sclerotiorum and B. cinerea in carrots destined for the processing market where any ozone-induced discoloration would be removed during peeling.