Department of Postharvest Science of Fresh Produce, Volcani Center ARO, Bet Dagan 50250, Israel
Modified atmosphere packaging (MAP) of persimmon fruit resulted in the accumulation of acetaldehyde to a level of 80 μg/ml; ethanol to a level of 900 μg/ml; and CO2 up to 30%. When fruits were stored at -1°C for 4 months in such atmospheres, the incidence of black spot disease, caused by Alternaria alternata, was reduced. The effects of each of these gases were examined to determine their individual involvement in the inhibition of Alternaria development during storage. When A. alternata, grown at 20°C on potato dextrose agar or inoculated in persimmon fruit, was exposed for 24 h to different levels of each volatile, acetaldehyde was the most fungistatic but only at concentrations higher than those that accumulated under MAP; CO2 was moderately inhibitory at concentrations from 10 to 60%, whereas ethanol had no effect. Similar inhibitory effects were obtained with acetaldehyde at 620 μg/ml or 30% CO2 when in vitro cultures of A. alternata and infected fruits were exposed for up to 2 weeks at 20°C, but 1,000 μg of ethanol per ml had only a transitory inhibitory effect under these conditions. Based on analysis of the effect of concentration versus time for each gas accumulating in MAP, we suggest that the increasing concentration of CO2 during storage is the principal factor in the inhibition of black spot disease development.