Globally, one-third of the food produced for human consumption is lost or wasted, according to the Food and Agriculture organization of the United Nations. That’s about 1.3 billion tons per year.
Researchers with Tufts University’s Department of Biomedical Engineering are searching for a new way to preserve perishable foods. Publishing in Scientific Reports today, the team reported on their preservation method that kept fruits fresh for more than a week without refrigeration.
“Many perishable fruits and vegetables possess in fact high metabolic activity and suffer from high possibility of microbial contamination, resulting in short shelf life, fungal decay, color change, and off-flavor,” the researchers wrote. “To date, several treatments have been explored to extend the postharvest life of fruits and vegetables (e.g. cryopreservation, exposure to synthetic chemical fungicides, modified atmosphere packaging, osmotic treatments, hypobaric and heat treatments).”
In their work, the researchers studied the efficacy of silk fibroin, an odorless and tasteless silk solution that is invisible. An insoluble protein found in silk, fibroin boasts the ability to stabilize and protect other materials. It is biocompatible and biodegradable. The researchers said that silk’s crystalline structure makes it naturally tough.
The researchers dipped fresh-picked strawberries in a 1 percent silk fibroin protein solution, and repeated the process four times. Afterwards, the coated strawberries were treated with water vapor under vacuum for differing amounts of time in a water-annealing process. This resulted in varying percentages of crystalline beta-sheets in the coating.
“An increased beta-sheet content corresponds to a reduction in oxygen diffusion through silk fibroin thin films,” the researchers wrote. The longer the exposure, the more robust the fibroin sheets. The coatings were between 27 and 35 microns thick.
Following the coating process, the strawberries were stored at room temperature and compared to uncoated berries. After one week, the researchers found that the higher beta-sheet silk berries were in noticeably better condition than their counterparts.
“The beta-sheet content of the edible silk fibroin made the strawberries less permeable to carbon dioxide and oxygen,” said Prof. Fiorenzo Omenetto, who contributed to the study, in a statement. “We saw a statistically significant delay in the decay of fruit.”
The researchers also tested the method on bananas. On day nine, “the flesh of non-coated bananas presented a brown color, while silk-coated fruits preserved a tallow flesh, indication of a decreased ripening rate within the silk-coated sample,” the researchers wrote.
The new coating material may further be enhanced by adding therapeutic properties that don’t require complex chemistries, the researchers added.
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