The study’s results suggested bananas can be bred with higher levels of carotenoids.
These compounds are found at various levels in different banana cultivars and are important vitamin precursors for eye health.
The findings are especially relevant to areas of Africa and Southeast Asia.
The World Health Organisation (WHO) estimates that more than 250 million children aged one to four years in 122 countries in Africa and South-East Asia are at the risk of vitamin A deficiency.
Researchers from the Queensland University of Technology began looking at two banana varieties to determine why they produced varying amounts of carotenoids.
They found the fruits of both the Cavendish and Asupina cultivars increased in size throughout development with immature fruits emerging with green peel and white pulp.
The peel and pulp of the Cavendish fruit gradually changed to yellow through fruit development, whereas Asupina changed to deep orange.
The colour changes in both cultivars were in keeping with increased carotenoid accumulation during fruit development.
Lutein, α-carotene and β-carotene were found in the pulp of both cultivars, but the percentage composition and quantity of total carotenoids varied between the two.
Lutein was the predominant carotenoid in early stages of development in both cultivars and remained so until fruits reached full-ripe (FR) stage in Cavendish.
However, as the fruits matured, the β-carotene content in the Asupina variety made up 70.6% of total carotenoids by the FR stage.
“The Asupina variety accumulated higher amounts of total carotenoids than the Cavendish variety throughout fruit development, but the difference was more pronounced between the two cultivars during the transition to mature full green (FG) and FR fruit stages,” the researchers wrote.
They said these key differences between varieties was the result of greater activity of the enzyme carotenoid cleavage dioxygenase 4 (CCD4) in the Cavendish variety, which broke down more of the carotenoids.
CCD4 was most likely responsible for the conversion of amyloplasts to chromoplasts during fruit ripening in the Asupina variety resulting in even higher levels of carotenoids in this variety.
Little banana research
Previous research has focused on methods to increase carotenoid content in bananas.
It is generally acknowledged that the compounds, which turn fruits and vegetables red, orange or yellow, are converted into vitamin A in the liver.
However, what has stumped researchers is exactly how bananas produce and store carotenoids.
Carotenoid levels in mature fruits from a number of different banana cultivars have been reported.
However, very little data is available on how carotenoid accumulation is regulated during fruit development.
The paper detailed the complexity of carotenoid biosynthesis, commenting that changes in composition that occurred throughout the plant’s life cycle added to the difficulty in determining the mechanisms involved.
Studies that have established a link in carotenoid gene expression during fruit ripening with changes in carotenoid content have been carried out although not in bananas.
“Taken together, our results suggest that CCD4 expression may contribute to the low carotenoid status of Cavendish fruit,” the paper concluded.
“However, the primary difference accounting for the variation between Asupina and the low-carotenoid-accumulating Cavendish bananas is likely due to enhanced storage sink strength in Asupina resulting from the formation of chromoplasts in mature fruit.
“These insights should prove important in the future for the development of banana biofortification strategies.”
Source: Journal of Agricultural and Food Chemistry,
Published online ahead of print, DOI: 10.1021/acs.jafc.5b05740
“The Quest for Golden Bananas: Investigating Carotenoid Regulation in a Fe’i Group Musa Cultivar.”
Authors: S. Buah, B. Mlalazi, H. Khanna, J. L. Dale and C. L. Mortimer