Ripening requirements and changes of "saba" bananas (Musa, BBB group) treated with ethylene from Gliricidia leaves (Gliricidia sepium Steud)

GL [Gliricidia leaves] at 5% of fruit weight was sufficient to uniformly ripen fruits 2 d after a 24-h treatment while untreated fruits ripened over a range of 5-16 d after harvest. This was due to ethylene which increased up to 3-6 ppm in 24 h. GL was as effective as rain tree leaves (Samanea saman Merr.) with or without calcium oxide as CO2 scrubber. In comparison to calcium carbide (CaC2) applied at 25 gram per 100 fruits for 24 h and 1000 ppm Ethephon as 5-min dip, GL delayed ripening by 1 d due to lower ethylene levels during the first 12 h of treatment. It only accumulated to about 0.3 and 1 ppm after 6 h and 12 h, respectively. For constant levels of ethylene at these concentrations to induce ripening, 24- and 12-h exposure periods were required, respectively. For 3.5 ppm ethylene which was approximately the ethylene content of Ethephon-dipped fruits immediately after dipping, 8 h was required. CaC2 released more than 10,000 ppm acetylene which is ten times higher than the inductive level for ripening. Low O2 resulting from GL treatment retarded ethylene response while high CO2 did not. Ripening was delayed by 1 d at 10% O2 during 24-h treatment with 0.4 ppm ethylene relative to that at 13% O2 or higher even in the presence of 8% CO2. Such delaying effect was negated when applied ethylene was increased to 1.2 ppm. Ripening of GL-treated fruits was initiated on the eighteenth hour of treatment as manifested by marked increases in the production and internal levels of ethylene and CO2 and decrease in internal O2. Ethylene rise was initially due to increased ethylene-forming enzyme (EFE) activity in the pulp. Subsequently, further increase in EFE was preceded by increased 1-aminocyclopropane-1-carboxylic acid (ACC) levels. These changes occurred earlier in the pulp than in the peel. Normal ripening-associated processes were induced as indicated by similar physico-chemical and sensory attributes of bioethylene-ripened fruits and normally ripened fruits. However, GL-treated fruits lost less weight, did not shrivel and had better appearance than untreated ones.