Research with a peel: FSU study on banana browning could help fight food waste

A research image showing the progression of browning on a banana over five days. (Oliver Steinbock/Florida State University)

New research from Florida State University won’t just help you time your banana bread, it could also help reduce millions of tons of food waste from widely grown fruits.

A team of FSU researchers studied the formation and spread of brown spots on bananas, a striking case of biological pattern formation. In research published in Physical biologythe team described how the spots appear for a two-day window, expand rapidly, but then mysteriously settle, leaving a clear distinction between brown spots and skin that is still yellow.

Oliver Steinbock, professor in the Department of Chemistry and Biochemistry
Oliver Steinbock, professor in the Department of Chemistry and Biochemistry

“You can look at fairly old bananas and you’ll see these brown spots but with dark yellow regions in between,” said Oliver Steinbock, a professor in the Department of Chemistry and Biochemistry and lead author of the paper. “They never really invaded those areas. They just stopped. It’s scientifically interesting because it might tell you something about the mechanism that causes browning.

Brown spots appear on bananas when oxygen reacts with an enzyme in the skin of the fruit and causes the production of dark pigments. Steinbock and his team wanted to understand how the spots appear and spread, and why they adopt the dot patterns so characteristic of this staple.

Using time-lapse videos, the researchers measured how often the dark spots formed and how quickly they spread over a week. They used this information to develop a model describing the rate of the reaction and the movement of oxygen through the skin. This model is now a tool for understanding the browning process and for further studies.

Previous research has found that browning comes from tiny skin pores called stomata where oxygen can enter, but skins contain many more of these pores than dark spots. The researchers wondered why the reaction only seems to occur in certain places.

Their suggestion is that defective pores allow oxygen to enter. Oxygen spreads from this defect, but the skin reacts quickly, resulting in a sharp contrast between brown and yellow. When oxygen stops penetrating the skin – perhaps because the offending stomata collapse – the expansion of the spot abruptly stops.

“That’s the picture we developed based on our model and our measurements,” Steinbock said. “But what exactly does it take to make this happen? Is it a rogue pore behaving badly? Is it a small group of stomata? This is a difficult question to answer at the moment. »

Bananas are among the most popular fruits in the world. According to the International Institute for Sustainable Development, farmers grew about 117 million tons in 2019, but about 50 million tons ended up as waste. Visually unappealing fruit is a major contributor to spoilage, making efforts to understand and inhibit the browning process important. Instead of turning overripe fruit into an ingredient for banana bread or storing it in a freezer, consumers often skip brown bananas in the produce section or toss them in the trash at home.

The fruit is an important crop for countries around the world, which makes it even more crucial to understand how they ripen.

“It’s really a very tricky business because bananas are very complicated systems,” Steinbock said. “If you chill them, you slow down the browning, but you spoil the taste. You can spray something on the surface to reduce gas exchange, but that will indirectly change the taste. It’s not an easy problem.

Postdoctoral researcher Qingpu Wang and former graduate student Pamela Knoll were co-authors of this study. This research was supported by the National Science Foundation.


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