Chemistry

Edible Silk Coating Stops Fruit And Veg Going Moldy

We’ve all made the mistake of buying a bunch of bananas that’s just a little too big, and then finding ourselves in a race against time to eat them all before they go brown. Fortunately, the days of having to use our mushy leftovers for banana bread could soon be over, after a team of researchers developed a silk coating that appears to prevent fruit from going moldy, even when kept at room temperature.

Describing their experiments in the journal Scientific Reports, the study authors explain how silk fibroin – a structural protein that’s similar to collagen – boasts a number of unique properties that make it the perfect material for use in cocoons. For instance, the fact that it consists of alternating hydrophobic and hydrophilic (meaning water-resistant and water-attracting) blocks ensures that water evaporation can be controlled, as can the diffusion of gases such as oxygen and carbon dioxide – all of which makes for a happy pupa.

Since perishable foods ripen as a result of cell respiration, manipulating water evaporation and gas diffusion is also likely to hold the key to stopping fruit and veg from going bad. The team therefore created a silk fibroin dip, which they dunked strawberries into, leaving an invisible, micrometer-thin coating on the surface of the fruit.

After leaving these silky strawberries in a room-temperature environment for a week, the researchers found that they retained their firmness, colour, and juiciness, while uncoated strawberries left in the same environment wasted away.

When coated with the silky fibers, strawberries stayed fresher for longer. Scientific Reports/Marelli, B. et al

Importantly, the silk coating is also edible, containing small amounts of metal elements that are well below the toxicity levels for drinking water as established by the World Health Organization.

Summing up the results of this experiment, lead researcher Fiorenzo Omenetto explained that “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.”

To confirm this, the team then used the coating on bananas, noting that, nine days later, they remained firm and yellow while uncoated bananas had long since turned brown.

Aside from providing the study authors with a fruit salad, the results of this work could have major implications regarding access to food on a global scale. According to the United Nations Food and Agriculture Organization, roughly one-third of all food produced around the world goes to waste, with this figure rising to 50 percent for perishable fruit and vegetables. The majority of this wastage is caused by “premature deterioration,” as foodstuffs decay along the supply chain before they reach consumers’ mouths.

Given that fridges are not always available when food is being transported and stored, the use of coatings such as this to prolong the life of crops could one day save huge quantities from perishing.

On the downside, there’ll be less banana bread.

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