The perishables supply chain may become much easier to manage, thanks to the development of a new type of ultra-thin wrap that is capable of keeping fruit fresh for more than a week, without refrigeration or plastic.
The fibroin-based wrap may play a part in reducing both the energy consumption and the waste generated by the food packaging and logistics industry, as farmers and companies seek to keep fruits and vegetables fresh between the farm and the consumers' shelves. Despite the plastic and refrigeration used, around 50 percent of the world's food is lost to spoilage before people can eat them.
Researchers from Tufts University in Massachusetts developed a new type of edible, spray-on coating from fibroin, an insoluble protein that forms the basis of silk's strength.
The researchers dipped perishable fruits like strawberries and bananas into a solution of fibroin, then exposed the fruit to water vapour under a vacuum. Depending on the amount of time spent there, the fruits developed different percentages of coatings. The thickest coating, at 58 percent was 35 microns thick, which is still invisible to the naked eye.
To test the coating, the researchers stored the coated produce at 22 degrees Celsius, alongside uncoated fruit, for seven days. At the end of the experiment, the uncoated strawberries had discoloured and lost their texture, while the berry with the 58 percent coating was still plump and fresh. The strawberry with 23 percent coating, meanwhile, also experienced a degree of spoilage.
According to the scientists, the silk coating slows down the respiration of the fruit.
"The beta-sheet content of the edible silk fibroin coatings made the strawberries less permeable to carbon dioxide and oxygen," said lead researcher Fiorenzo G. Omenetto. "We saw a statistically significant delay in the decay of the fruit."
Bananas performed similarly. The researchers started with green bananas and over the course of nine days, both were allowed to ripen. While the banana with the silk fibroin coating still ripened under the wrap, it did so more slowly.
While silk fibroin is generally flavourless and odourless, the scientists are hoping to further test if the coating compromises the taste of the food. However, they have tested the toxicity of the food wrap, and found it to be significantly below the toxicity levels in drinking water, making the wrapping safe to eat.
The team hopes to eventually scale-up the production of the coating, and make it cheaper and easier for farmers and supermarkets to use than plastic.