EVALUATION OF HEATED SOLUTIONS OF SULFUR-DIOXIDE, ETHANOL, AND HYDROGEN-PEROXIDE TO CONTROL POSTHARVEST GREEN MOLD OF LEMONS

Lemon fruit were inoculated with spores of Penicillium digitatum and immersed in solutions of ethanol, sulfur dioxide, or hydrogen peroxide to control postharvest green mold. Green mold incidence and fruit injury were assessed after treatments employing various combinations of concentration, duration of treatment, temperature, and post-treatment rinses. Heating of the solutions was needed to attain acceptable efficacy. Sulfur dioxide and ethanol controlled green mold without injury to fruit, whereas hydrogen peroxide did not effectively control green mold and caused unacceptable injury to fruit. Treatments selected for extensive evaluation were immersion in 10% ethanol at 45 degrees C for 150 s without rinsing, or in 2% sulfur dioxide at 45 degrees C for 150 s followed by two fresh water rinses. These treatments were compared with two existing decay control methods: immersion in 3% sodium carbonate at 45 degrees C for 150 s followed by two fresh water rinses, or in 1,000 mu g/ml imazalil at 25 degrees C for 60 s. Lemons were inoculated at 20 degrees C then incubated for 12, 24, 48, or 60 h before treatments were applied. Efficacy of sulfur dioxide and ethanol treatments was comparable to that of sodium carbonate and imazalil. Sulfur dioxide and ethanol did not injure the fruit and their residues were low. The sulfur dioxide content of lemons immediately after treatment was less than 1 mu g/ml. The ethanol content of lemons analyzed immediately after ethanol treatment was 58.6 (+/-9.6) mu g/ml and 24.4 (+/-11.7) mu g/ml after storage for 7 days at 20 C. The ethanol content of untreated fruit was 3.3 mu g/ml.