Exploring the significance of photosynthetic activity and carbohydrate metabolism in peel tissues during banana fruit ripening

Abstract

Starch synthesis and degradation in banana pulp have been extensively characterized. However, no literature studies are currently available on these processes in the peel, except concerning the presence of starch granules. Thus, this work explored the potential connection between photosynthetic activity and starch accumulation in banana peel. Bananas, cultivar Nanicão, were analyzed at different development and ripening stages. The chlorophyll a fluorescence values for green banana peels indicated that the photosystems were active before fruit ripening, concomitant to starch accumulation. During banana ripening, accumulated starch is degraded concomitantly with an increase in soluble sugars, such as those occurring in the pulp. For comparison, the peel and pulp starch granules were characterized during the fruit ripening. The results showed that the peel starch granules presented higher amylose contents than the pulp, and SEM images exhibited similar patterns of granules, shapes, and sizes. As ripening advanced, starch granules from the peel appeared to undergo different degradation steps, and the appearance of starch fragments of different sizes indicated an apparent weakness, probably due to the low structural complexity of their components, amylose and amylopectin.