Designing Silk Coats for Fruit, to Help Them Stay Fresh

By Ruth Kava — May 06, 2016
Maintaining freshness of fragile fruits, such as berries, is a daunting issue since they rapidly lose water and quickly become unappealing. But some new technology using the silk protein fibroin may soon help tackle this source of food waste. 


shutterstock_165452462 Strawberries via Shutterstock

Silk is known for its strength and flexibility. Its numerous applications include clothing, parachutes and, most recently fruit preservation. A recent report in Scientific Reports describes the formation of a coating for fragile foods from fibroin, the protein found in silk.

Dr. B. Marelli, and colleagues from the department of Biomedical Engineering of Tufts University, described the process by which they designed a water-based suspension of fibroin that forms a coating on foods dipped into it. By first dipping the fruit in a fibroin solution, then treating it with water (water annealing), they formed a film on the fruit that consisted of various percentages of a beta-sheet structure of the protein, which was the form that was most protective.

Fragile foods, such as strawberries and other thin-skinned fruits, will lose water and dehydrate rapidly under room temperature conditions. But the researchers demonstrated that the fibroin coating can reduce the loss of water and the passage of gases, such as oxygen and carbon dioxide, into and out of the fruit. This slows the metabolism of the fruit and thus delays spoilage, enhancing the shelf life.

Indeed, the study authors demonstrated that after seven days under room conditions, strawberries with a fibroin coating that contained 59 percent beta-sheet structure lost significantly less water and looked much fresher than uncoated berries. Further, using this coating on bananas also resulted in delayed ripening and browning of the fruit. And this coating is edible — it's just another protein that the human digestive system can break down.

According to the Food and Agriculture Organization of the UN, food waste at the consumer level in industrialized countries is on the order of 222 million tons per year. This is about 40 percent of total food losses in those countries. While lengthening the shelf life of some fruits and vegetables won't solve the global food wastage problem, if such a method becomes economically feasible, it should certainly benefit both retailers and consumers.