Finding the beauty – and value – in brown bananas

Today is International Plant Health Day – a perfect opportunity to talk about how society shuns blemished bananas.

As it turns out, it’s not how you look on the outside, but how you peel.

Over 900 million tonnes (17%) of edible food is wasted globally per year – and this is the stuff that actually makes it into our shopping baskets. A lot of produce doesn’t make it that far, and even more doesn’t make it to the stores. This is because we’ve selected for fruits and vegetables by their looks alone. This extends to bananas, where an estimated 50 million tonnes of the fruit are thrown out by stores and consumers based only on its appearance.

A team of researchers at Florida State University, US, have developed a new model of simulating banana spot patterns, improving our understanding of how and why fruits brown over time, and potentially preventing some of this fruit from going to waste when still perfectly edible. Their findings have just been published in Physical Biology.

Fruit browns over time from cuts, damage or long-term storage, but we usually associate this with the level of ripeness. The browning process is dependent on enzymes, including polyphenol oxidase (PPO), reacting with natural phenols and oxygen in the air, to produce benzoquinone and melanin, a group of brown pigments.

“For 2019, the total production of bananas was estimated to be 106 million tonnes, making it a leading crop in the world,” says Dr Oliver Steinbock, lead author of the research. “When bananas ripen, they form numerous dark spots that are familiar to most people and are often used as a ripeness indicator. However, the process of how these spots are formed, grow, and their resulting pattern remained poorly understood, until now.”

Using timelapse videos, the group used a nonlinear reaction-diffusion model, including the oxygen concentration and browning degree of the peel, to predict how spots form and evolve over time. They found that spots rapidly appear during a two-day window to a density of about eight spots/cm2, but then suddenly stall. This mysterious deceleration of browning is likely to be due to changes in the oxygen level, possibly brought on by a collapse of stomata as the peel browns. With this information, the team suggested an a-peeling strategy to help combat the browning process: by decreasing the oxygen levels available to stored bananas, we can potentially slow the formation of spots.

“Fruit browning continues to be a major challenge for the food industry. Our study offers a model for banana spotting which is capable of capturing their evolution in a physically meaningful context and which can be applied to procedures to mitigate food waste,” Steinbock concludes. 

A time-lapsed banana peel browning simulation. Credit: Oliver Steinbock

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