2019 ASHS Annual Conference

For bananas held at or above the chilling threshold temperature, usually considered to be 13°C, ripening is the major shelf life limiting factor. However, extending banana shelf life at or near its chilling threshold by delaying ripening could shift the shelf life limitation to another factor, possibly chilling injury. Therefore, we considered treating green bananas with the ethylene action inhibitor, 1-methylcyclopropene (1-MCP), to test the hypothesis that delaying ripening at the chilling threshold temperature, thus allowing longer exposure to that temperature, would result in development of chilling injury. However, prior to testing that hypothesis, it was necessary to determine an appropriate 1-MCP concentration to delay ripening while still allowing eventual ripening recovery. Rather than using the typical 12- to 24-h gaseous 1-MCP treatment procedure, we used a 1-minute immersion in aqueous 1-MCP solution, which has been shown to exhibit similar efficacy (Choi and Huber, 2008). Freshly delivered mature green bananas were obtained through a local retail store and the hands were cut into individual fingers and randomized. Half the fruit were treated with 100 μL/L ethylene for 24 h at 20°C (+ETH) and the other half held in air at 20°C (-ETH). Bananas were immersed in 0, 10, 25, or 50 μg/L 1-MCP (a. i.) solution at 23°C for 60 s followed by air drying. Ripening features were evaluated every 1 or 2 d at 20°C based on the rate of ripening. The ripening of ethylene pre-treated green bananas was little affected by 1-MCP, but the ripening of control (no ethylene pre-treatment) fruit was significantly delayed. Control fruit immersed in 0, 10, 25, or 50 μg/L 1-MCP reached ripeness stage 7 (yellow with brown flecks) after 27, 29, 37, and 39 days, respectively, while ethylene-treated fruit required 11-15 days. Peak climacteric respiration for ethylene-treated fruit occurred on days 5-6, while for the control it was 15, 21, 30, 31 d for 0, 10, 25, 50 μg/L 1-MCP, respectively. Bananas ripened without ethylene, especially those with 1-MCP treatment, had less bright appearance corresponding to lower L and b* values than ethylene-treated fruit without 1-MCP. It is possible the carotenoid biosynthesis pathway in the peel was affected by the inhibition of ethylene action via 1-MCP. To conclude, the minimum effective 1-MCP concentration for a 1-min aqueous application to delay banana
ripening at 20°C was 25 μg/L, which resulted in a 10-d extension over the 0 μg/L 1-MCP/-ETH treatment.