Softening response of banana fruit treated with 1-methylcyclopropene to high temperature exposure

Elevated temperatures experienced by harvested fruit can modulate their ripening. Moreover, heat treatments can be applied to reduce susceptibility to low temperature disorders and to help control pests and diseases. The ethylene-binding inhibitor 1-methylcyclopropene (1-MCP) was used to investigate the ethylene-mediated softening response of banana fruit exposed to elevated temperatures. A preliminary experiment was conducted to determine levels of high temperature (30-50 degreesC) imposed for a short period of time that did not cause skin scald. The softening response of Williams banana fruit treated with 1-MCP at various temperatures and durations was characterised in subsequent experiments. Exposure of fruit to hot air for 60 min at 45 degreesC or for 30 min at 50 degreesC caused 30-40% peel scald. The peel was not visibly damaged for fruit treated at 40 degreesC for up to 60 min. Softening of fruit treated with 1-MCP for 12 h at 25 degreesC and then held for 7 days at 30, 35 or 40 degreesC was inhibited in proportion to increasing concentration over the range 0.01-1 mul/l 1-MCP. However, softening was progressively enhanced with increasing holding temperatures from 30-40 degreesC and/or time from 1-7 days, although fruit treated with the higher 1-MCP concentrations of 1 and 10 mul/l were comparatively less responsive to heat. Although banana fruit held at 30-40 degreesC did not de-green, their increased softening at elevated temperatures and inhibition of this response by 1-MCP suggest that heat enhances synthesis of new ethylene sites which mediated banana fruit softening.