It’s a tale as old as time — or, as old as commercial farming and refrigeration. You scoop up a clamshell of gleaming red strawberries in the supermarket, take it home, and snack on your favorite seasonal fruit.
But then, almost as quickly as they came into your possession, you lose nearly half of those berries to mold in just a couple of days.
As it turns out, strawberries in particular are considered a highly perishable fruit.
“The strawberry is a fruit that has very high respiratory activity and a very low pH [acidity],” University of São Paulo Professor Stanislau Bogusz Junior explained. “It’s therefore very susceptible to microbial attack. It’s also very moist and the fruit is small.”
This — and the fact that strawberries have one of the highest loss rates in Brazilian supermarkets — inspired researcher Mirella Romanelli Vicente Bertolo, overseen by Professor Bogusz, to create a solution.
Bertolo and her research team at the São Carlos Institute of Chemistry of the University of São Paulo created an edible “biofilm” obtained from agricultural waste to extend the shelf-life of strawberries.
Her inquiry began during her doctoral studies under Professor Bogusz. During this time, they developed a technique that allowed them to extract antioxidants — substances with preservative properties — from the peel of a pomegranate.
“More than 40% of the pomegranate, depending on the variety, is made up of peel, which is wasted,” Bogusz explained in a statement.
“Our idea was to use this waste to obtain extracts rich in phenolic compounds with antioxidant and antimicrobial activities.”
Once they successfully had an extraction method, the researchers incorporated the antioxidants into coatings based on gelatin and chitosan.
Chitosan is a polymer found in the bodies of crustaceans — like shrimp or squid.
Bogusz said that they used the chitosan extracted from the inner shells of squid because it doesn’t cause the same problems of allergies like shrimp do.
“And we combined this material with another polymer, in this case gelatin, to improve its mechanical properties.”
It was then that they successfully developed a protective film for strawberries, as published recently in the journal Food Chemistry.
In laboratory tests, the researchers found that over 12 days of refrigerated storage, strawberries coated with the film lost 11% weight and took between six and eight days to start becoming contaminated with fungi, compared to just four days for fruit not covered with the film.
“By applying the coating, it was possible to double the shelf life of strawberries kept under refrigeration and delay the dehydration of the fruit, while preserving the taste, texture and volatile compounds that give the fruit its characteristic aroma,” Bertolo said.
The findings conclude that the material forms a film on the surface of the fruit, acting as a barrier to the passage of microorganisms (like mold), moisture loss, and gas exchange.
This modifies how much respiration the strawberry has and slows down the metabolism of the fruit after it’s been harvested.
In summary: This biofilm could keep strawberries in better condition for longer, maintaining the firmness, color, and flavor of the fruit.
“The results of the tests showed that there were no differences in the taste, aroma or visual characteristics of strawberries coated with the material compared to strawberries without the film,” Bertolo said.
Bogusz hypothesized that the material would also be effective on any other fruit.
This is a significant breakthrough, considering an estimated 40-50% of fruits and vegetables are wasted each year globally, translating to roughly 670 million tons of food.
While preventing food waste through proper storage and preparation can help, this discovery may also be part of the solution.
The researchers have filed a patent application for the formula and intend to license the technology to interested companies. Economic analyses show that the coating could cost an estimated 0.15 Brazilian Reals (or 0.02 USD) per fruit.
Bertolo concluded: “This is a cost that consumers may be willing to pay for fruit with a longer shelf life and greater usage.”
Header image by Engin Akyurt/Pexels
