Ozone and 1-methylcyclopropene alter the postharvest quality of broccoli

Fresh broccoli (Brassica oleracea L. Italica group) florets untreated or treated with 1 muL/L-1 1-methylcyclo-propene (1-MCP) for 14 h, were stored at 12 degreesC with 0, 200, or 700 nL.L-1 ozone. Senescence parameters were evaluated after 0, 1, 2, 5, 8, or 12 days of storage. Treatment with 1-MCP delayed the yellowing of florets, and at day 5 the hue angle of 1-MCP treated florets was 116degrees (green) compared to 102degrees (yellow) for the control. Respiration rates of florets were reduced by 1-MCP for the first 5 days. The 1-MCP treatment maintained higher chlorophyll fluorescence expressed as F-v/F-m during 12 days of storage. Also, 1-MCP reduced dimethyl trisulfide production, which contributes to off-odor development in broccoli florets. Compared with the controls, florets stored in 200 nL.L-1 ozone had less mold growth and yellowed more slowly, but no differences were observed in respiration, ethylene production, or F-v/F-m. Florets stored in 700 nL.L-1 ozone were greener than florets held in air or 200 nL.L-1 ozone. Interestingly, chlorophyll fluorescence of the florets stored in 700 nL.L-1 ozone decreased significantly and at day 12, F-v/F-m was only 30% of its initial value. Ozone at 700 nL.L-1 stimulated respiration and ethylene production of florets after 1 day of storage, and caused visible damage in the form of increased weight loss and browning of the floret stem ends. Treatment of broccoli with 1-MCP alone or in combination with 200 nL.L-1 ozone maintained the quality and extended the shelf life of broccoli florets.