Keeping fruits and vegetable fresh for one week is enough for world food traders and transporters and if it involves silk and not refrigeration, then it is world’s great discovery.
Researchers from Tufts University have demonstrated that fruits can stay fresh for more than a week without refrigeration if they are coated in an odorless, biocompatible silk solution so thin that it was invisible. The new method is likely to provide an alternative to food preservation technology that is expensive, especially when it is to be transported to far off places or continents.
Using a naturally derived material and a water-based manufacturing process, 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 stabilize and protect other materials while being fully biocompatible and biodegradable, said the study published in the May 6 issue of Scientific Reports.
Researchers dipped freshly picked strawberries in a solution of 1 percent silk fibroin protein; the coating process was repeated up to four times. The silk fibroin-coated fruits were then treated for varying amounts of time with water vapor under vacuum (water annealed) to create varying percentages of crystalline beta-sheets in the coating. The longer the exposure, the higher the percentage of beta-sheets and the more robust the fibroin coating. The coating was 27 to 35 microns thick.
The strawberries were then stored at room temperature. Uncoated berries were compared over time with berries dipped in varying numbers of coats of silk that had been annealed for different periods of time. At seven days, the berries coated with the higher beta-sheet silk were still juicy and firm while the uncoated berries were dehydrated and discolored.
Tests showed that the silk coating prolonged the freshness of the fruits by slowing fruit respiration, extending fruit firmness and preventing decay. Similar experiments were performed on bananas, which, ripened early compared with uncoated controls and added firmness to the fruit by preventing softening of the peel. The silk coating did not affect fruit texture.
“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,” said author Fiorenzo G. Omenetto, professor in the Department of Biomedical Engineering.
According to the Food and Agriculture Organization (FAO) of the United Nations, half of the world’s fruit and vegetable crops are lost during the food supply chain, due mostly to premature deterioration of these perishable foods.