Bananas can be kept fresh by blocking their breathing, a study has found.
Covering the fruit with a special film made them ripen more slowly by reducing their ability to absorb oxygen.
It also killed the bacteria that cause over-ripe bananas to rot.
The coating used was made from chitosan, a material derived from shrimp and crab shells.
Study leader Dr Xihong Li, from Tianjin University of Science and Technology in China, said: "We found that by spraying green bananas with a chitosan aerogel we can keep bananas fresh for up to 12 days.
"Once bananas begin to mature, they quickly become yellow and soft, and then they rot. We have developed a way to keep bananas green for a longer time and inhibit the rapid ripening that occurs.
"Such a coating could be used a home by consumers, in supermarkets or during shipment of bananas."
The research was presented at the annual meeting of the American Chemical Society in Philadelphia.