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The 2011 ASHS Annual Conference

5514:
Evidence for Oxidative, Free Radical-Mediated Metabolism of 1-Methylcyclopropene In Fresh-Cut Tissue and Cell-Free Homogenates of Apple Fruit

Sunday, September 25, 2011
Kona Ballroom
Jinsu Lee, Horticultural Sciences Department, Horticultural Sciences Department, IFAS, University of Florida, Gainesville, FL
Donald J. Huber, Horticultural Sciences Department, University of Florida, Gainesville, FL
Christopher B. Watkins, Department of Horticulture, Cornell University, Ithaca, NY
Previous studies have demonstrated significant and variable non-target sorption of 1-MCP by fruit and vegetables. In many cases, sorption is markedly enhanced upon tissue processing (slices). In this study, non-specific sorption of 1-MCP was examined in fresh-cut tissues and cell-free homogenates (CFH) of five apple cultivars. Fruit were processed into cubes of approximately 10 g, enclosed in sealed jars, and provided with 20 µL L-1 gaseous 1-MCP. There were significant differences in the sorption of 1-MCP by fresh-cut tissues from different apple cultivars. Fresh-cut ‘Jonagold’ and ‘McIntosh’ absorbed 1-MCP over 6 h with the highest capacity showing 97.5 ± 0.46 and 97.6 ± 0.40%, respectively, followed by ‘Cameo’ at 93.9 ± 0.08%. ‘Honeycrisp’ had the lowest capacity with 88.5 ± 0.63%. Sorption rates showed a similar trend among cultivars. 1-MCP sorption rates for fresh-cut ‘Honeycrisp’, ‘Cameo’, ‘Jonagold’ and ‘McIntosh’ were 100.8 ± 0.4, 111.9 ± 3.6, 127.9 ± 3.1, and 130.9 ± 2.6 ng kg-1 s-1, respectively. Sorption of 1-MCP by CFH from the different cultivars paralleled the sorption by fresh-cut tissues. The similar patterns of 1-MCP sorption of fresh-cut tissue and CFH of different apple cultivars indicated that 1-MCP sorption was influenced by 1-MCP metabolism. The capacity to sorb 1-MCP was markedly influenced by tissue aging, with tissue of ‘Delicious’ aged for 6 h showing a 60% reduction in 1-MCP sorption compared with freshly prepared tissue., Removal of cut-surface tissue following tissue aging resulted in nearly 80% recovery in 1-MCP sorption rate and capacity. Therefore, wounding and aging operate in opposing fashion in controlling 1-MCP sorption in fresh-cut apple. The similarity of changes in oxygen consumption rate and 1-MCP sorption rate in fresh-cut tissue provided further evidence that oxidation contributes to 1-MCP metabolism in fresh-cut tissue. 1-MCP sorption rates over initial 2 h for fresh-cut tissue and CFH under 0.02 kPaO2 was reduced by 74 and 68%, respectively, compared with 20 kPaO2. Ascorbate inhibited 1-MCP sorption 82 and 65% in fresh-cut tissue and CFH, respectively. Hypotaurine, a quencher of the hydroxyl radical, suppressed 1-MCP sorption by fresh-cut slices and CFH by 88 and 68%, respectively. The data suggest that the oxidative burst associated with fresh-cut processing enhances sorption of 1-MCP through oxidative destruction. The data are consistent with free radical-mediated stress models for the surface of fresh-cut tissues (Acta Hort. 682:1819) and provide information useful in understanding the responses of fresh-cut fruit and vegetables tissues to 1-MCP.
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