Many of us avoid eating bananas when they start forming small brown spots, causing costly food waste.
Now, scientists say the formation of these spots can be slowed by limiting the oxygen levels available to microscopic skin cells.
Scientists have come up with a new method to simulate stain patterns on bananas, which offers new insights into how the world’s most famous fruits brown over time.
Preventing banana peels from turning brown could be the key to reducing food waste, according to the study’s authors.
Banana peels are the key to reducing tons of food waste. A new study explains the browning of this staple food
WHY DO BANANAS TURN BROWN?
A banana starts out as a deep green before changing to a delicious yellow and (if not eaten beforehand) an unappetizing brown.
But what causes this color change and what makes a banana go from green to the dark side? Apparently, bananas are a little too carbonated for their own good.
Bananas, like most fruits, produce and react with an airborne hormone called ethylene which helps signal the ripening process.
An unripe fruit is hard, more acidic than sugary, and likely has a greenish hue due to the presence of chlorophyll, a molecule found in plants that is important in photosynthesis.
When a fruit comes into contact with ethylene gas, the fruit’s acids begin to decompose, it becomes softer, and the green pigments of the chlorophyll are crushed and replaced – in the case of bananas, with a yellow hue.
However, unlike most fruits, which only generate a small amount of ethylene as they ripen, bananas produce a large amount.
While a banana early in the ripening process may become sweeter and yellow, it will eventually overripe by producing too much of its own ethylene.
High amounts of ethylene cause the yellow pigments in bananas to decompose into those characteristic brown spots.
This natural browning process is also observed when the fruit is bruised.
A damaged or bruised banana will produce even more ethylene, ripening (and browning) faster than if not damaged.
Source: Encyclopedia Britannica
Each year, 50 million tons of bananas end up as food waste, according to study lead author Oliver Steinbock of Florida State University.
“For 2019, the total banana production was estimated at 117 million tons, making it a leading crop in the world,” said Steinbock.
“As bananas ripen, they form numerous dark spots familiar to most people and often used as an indicator of ripeness.
“However, the process of formation, growth of these points and their resulting pattern has remained poorly understood, until now.”
Both the peel and the pulp of bananas are subject to browning, due to various scientific processes.
The pulp of many fruits turns brown when they are cut and not eaten immediately – not just bananas, but apples as well.
This happens because enzymes in meat react to oxygen in the air, a process known as enzymatic browning.
But banana peels also gradually turn brown as the fruit sits in the fruit bowl waiting to be eaten.
This is because banana peels contain a gas called ethylene, which breaks down chlorophyll, the chemical that keeps plants green.
The brown color comes from dark pigments including melanin, which is found in human hair and skin.
In bananas, these pigments form when oxygen reacts with natural chemical compounds called phenols in the peel.
As a banana turns browner and browner, much of the starch is converted into sugars, making it an excellent natural source of sweetness.
Despite this, the public is inclined to throw out brown bananas, even if they are still edible and ideal for use in cooking recipes.
For the study, the researchers used a combination of time-lapse video and a computer model to reveal how banana brown spots evolve.
The team’s computer model was used to consider oxygen concentration and degree of skin browning in the videos.
Oxygen from the air enters the peel in small holes called stomata, which explains why tiny spots form and spread, rather than the whole skin turning brown evenly.
The photos show the development of brown spots. The time between each of the photos is only one day
“Banana peel has a waxy outer layer that, when intact, does a great job of keeping oxygen out,” Steinbock told MailOnline. ‘The results are brown spots on a yellow skin.
“Very, very slowly, however, the oxygen eventually gets into the peel everywhere, so that a very old banana is completely brown.”
The researchers found that the spots appear and expand rapidly before their growth mysteriously stops, all within two days.
“Our results strongly suggest that the tiny holes collapse in the center of the brown spots,” Steinbock said.
“In doing so, they close the peel again, cut off the flow of oxygen and, consequently, the growth of the spots stops.”
Researchers have come up with a new method to simulate speck patterns on bananas, providing new insights into how this fruit turns brown over time.
Prevention of the browning process could be achieved with genetic modifications or better storage conditions, such as special containers with low oxygen levels.
Another potential protective mechanism for bananas is a thin coating to prevent oxygen from the air from entering the peel into its tiny holes.
Contrary to popular belief, a refrigerator is generally not a great place to put bananas after they have been brought from stores.
When we refrigerate unripe bananas that are still a little green, the pulp will not ripen at all but the skin will turn black.
Putting ripe bananas in the refrigerator will help them stay ripe (rather than overripe) for a few more days, however.
The new study was published in the journal Physical biology.
HOW A BANANA A DAY CAN KEEP HITS AT THE BAY
An eight-year study of 5,600 men and women over the age of 65 found that those with less potassium in their diets were 1.5 times more likely to have a stroke than those with the most people.
Since banana is a useful source of potassium, it can help reduce the risk of stroke in old age.
Other potassium-rich foods are lentils, oranges, and avocados.
Researchers at the Queen’s Medical Center of Hawaii have defined low potassium consumption as less than
2.4 grams per day and high intake of over four grams per day.
In Great Britain, the recommended daily dose is 3.5 g.
Strokes are one of Australia’s biggest killers and a leading cause of disability, while it is the third largest killer in the UK.