When used to coat green bananas, the spray made from a substance derived from shrimp and crab shells slowed their ripening and so kept them fresh for two weeks by forming a hydrogel coating on the surface.
Supermarket-bought bananas often go brown and soggy within two or three days. It is believed that the spray could help save millions of mushy bananas thrown away every day.
"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," Dr Xihong Li, who made the spray from chitosan, said.
"We have developed ways to keep bananas green for a longer time and inhibit the rapid ripening that occurs. Such a coating could be used at home by consumers, in supermarkets or during shipment of bananas," Li said.
The spray, which is being developed at Tianjin University of Science and Technology in China, is clear and tasteless and said to be completely safe.
It works by killing bacteria and slowing down the rate at which the fruit breathes. Bananas breathe by taking in oxygen and giving off carbon dioxide but do it through their skin.
The faster they breathe, the quicker they ripen, until they start to become soggy.
Bacteria on the skin then thrive and the banana rots. But an American Chemical Society conference heard the recipe has to be refined to make it suitable for commercial use.
Bananas are usually transported while still green and ripened in warm humid conditions similar to those they have experienced naturally.
Ethylene gas is used to start the ripening process. Bananas also produce ethylene as they ripen, which is why they rot faster when kept in a bag, as the gas builds up.
