Bananas (also other fruits and vegetables) emits gas called "ethylene." The presence of this gas inside the enclosed bags when transported for shipment coupled with high temperature hasten the fruit's ripening process. A food expert devised a new, low-cost treatment for prolonging the storage life of bananas and other fruits and vegetables during transport.
A charcoal-like material was placed inside a plastic bag which absorbs the ethylene gas given off by the bananas. It measures 15 x 15 x 2 cm. and soaked in a concentrated solution of potassium permanganate. Two slices were placed in each plastic bag containing a bunch of banana and tied at both ends with tape. They were cooled at a constant temperature of 20° C.
Those packed in plastic bag without the charcoal-like absorbent ripened in just two weeks. The treated ones remained hard green, as if newly harvested and when the plastic bag was taken off, the fruits ripened normally.
Source: Phil. Farmers' Journal July 1980