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Physiological Characterization of the Green Soft Disorder of Saba Banana
Thesis Abstract:
Saba bananas exhibited the green soft disorder (GSD) when subjected to modified atmosphere (MA) by sealing in 0.03 mm thick polyethylene bags (PEB) for longer than six days at 25°C. The oxygen (O2) levels in the bag were depleted to as low as 1-3 percent. Concomitant with the decline in O2 was the accumulation of carbon dioxide (CO2) to as high as 23 percent. Ethylene production in bananas under these conditions led to a build up of this volatile to a level of 28 ppm. Anaerobiosis was indicated by the presence of ethanol (EtOH) and acetaldehyde (AA) in the bags. GS fruits had fermented odor and flavor with pulp and peel discoloration. Anaerobiosis stimulated 1-aminocyclopropane-1-carboxylic acid (ACC) synthesis in GS fruits but the low O2 levels in the bags depressed the ethylene forming enzyme (EFE) activity. Despite the high levels of ACC, sustained ethylene production, which requires O2, was inhibited.
Low O2 was subsequently found to inhibit ethylene-induced peel color development but not pulp softening. Similarly, 20 percent EtOH and 10 percent CO2 inhibited peel color development without the concomitant inhibition of pulp softening. In contrast, AA could enhance pulp softening without significantly retarding peel color development. Under N2, which lead to very low O2 levels, both ethylene-induced pulp softening and peel color development were arrested.
The results of this series of studies were consistent with the hypothesis that the GSD arises from the combined effects of low O2, (5%) and threshold levels of ethylene which lead to anaerobiosis. Elevated CO2, EtOH, and AA in the fruits, which arise from anaerobic metabolism, inhibit peel color development but not softening.