Pathways of postharvest water loss from banana fruit

Abstract

Transpiration affects the water balance of the skin of a banana. The objective was to monitor the skin permeance in ripening bananas and to identify the mechanism(s) and pathway(s) of water vapor movement from skin to atmosphere. Transpiration was quantified gravimetrically. Cumulative transpiration increased linearly with time. Inducing ripening using ethylene increased autocatalytic ethylene production, induced a change in skin color from green to yellow, but had no effect on the skin water vapor permeance. The permeance was highest at the calyx end of the fruit but there was no significant gradient of permeance along the remaining axis or among the three faces of the fruit. A banana fruit surface is stomatous. About 11% of the stomata were infiltrated by aqueous acridine orange; about 63% of stomata were infiltrated if a silicone surfactant was added. The skin permeance was closely related to the density of the stomata that were infiltrated with acridine orange without the surfactant. We calculate about 44% of total transpiration was stomatal, the remaining 56% was cuticular. The permeance of a hypothetical astomatous cuticle was estimated to be about 0.66 ( ± 0.06) × 10−4 m s−1. Along the cuticular pathway, the wax offered the largest resistance to transpiration, followed by the cutin matrix and, last, the cell wall. Transpiration rate was positively related to temperature, but negatively related to relative humidity. The results indicate transpiration is a physical process that occurs in ripening banana to about nearly equal extents via the stomata and via the cuticle.