Scientists have invented a new silk-based alternative to clingfilm they claim can preserve food without refrigeration for more than a week.
Biomedical engineers, from Tufts University in America, say the edible, biodegradable silk solution is so thin it is virtually invisible to the eye.
They hope the material will be beneficial to the environment and reduce the amount of food wasted every year around the world.
Figures from the Food and Agriculture Organisation of the United Nations suggest that one third of all food is currently spoiled or squandered before it is consumed by people. Much of this is due to premature deterioration of these perishable foods.
According to the researchers, silk's unique crystalline structure makes it one of nature's toughest materials.
Fibroin, an insoluble protein found in silk, has a remarkable ability to stabilise and protect other materials while being fully biocompatible and biodegradable.
For the study, the researchers dipped freshly picked strawberries in a solution of 1% silk fibroin protein. The coating process was then repeated up to four times.
The strawberries were then stored at room temperature. Uncoated berries were compared over time with berries dipped in varying numbers of coats of silk.
At seven days, the berries coated with the most silk solution were still juicy and firm while the uncoated berries were dehydrated and discoloured.
Tests showed that the silk coating prolonged the freshness of the fruits by slowing fruit respiration, extending fruit firmness and preventing decay.
"The beta-sheet content of the edible silk fibroin coatings made the strawberries less permeable to carbon dioxide and oxygen. We saw a statistically significant delay in the decay of the fruit," senior study author Fiorenzo G. Omenetto said.
Similar experiments were performed on bananas, which, unlike strawberries, are able to ripen after they are harvested.
During the study the silk coating decreased the bananas' ripening rate compared with uncoated controls and added firmness to the fruit by preventing softening of the peel.
The thin, odorless silk coating did not affect fruit texture, but taste was not studied.
"Various therapeutic agents could be easily added to the water-based silk solution used for the coatings, so we could potentially both preserve and add therapeutic function to consumable goods without the need for complex chemistries," study author Benedetto Marelli added.
The study is published in full in the journal Scientific Reports.
