The post-ice cap Earth of 1995’s Waterworld presented a lot of unique challenges for Kevin Costner's Mariner and the rest of the characters, as they tried to eke out a living on the open water. Not least of these, was food scarcity.
We are a species particularly adapted to living on land. Fishing and hunting might deliver enough calories to keep a person alive, but maintaining solid health requires at least a few fruits and vegetables every now and then, and those are notoriously difficult to grow without soil.
As a consequence, food would have become increasingly valuable and the ability to preserve it for longer periods of time would be critical. These aren’t only challenges on the big screen; we produce more than enough food every year to feed every single person on the planet, meanwhile more than a billion people are impacted by food scarcity, driven at least in part by food waste.
Benedetto Marelli is a scientist at the Department of Civil and Environmental Engineering at MIT who is using insect silk to develop edible food packaging which extends the shelf life of fruits, vegetables, and meats. The results of his study were published in the journal Science.
During a food competition during his undergraduate studies, Marelli coated some strawberries with insect silk in an attempt to give them optical qualities like a diffraction grating. Shiny rainbow strawberries would have been neat, but the process didn’t work, and the strawberries were abandoned.
“The strawberries were left on the bench and some of them rotted while others didn’t. I recognized that was a peculiar result and saw an opportunity to apply these biomaterials to the agricultural field, which is in extreme need of innovation,” Marelli told SYFY WIRE.
Upon inspection, it was revealed that the strawberries which were coated in silk from the caterpillar Bombyx Mori hadn’t decayed at the same rate as the untreated strawberries. Something about the silk was preserving them.
Photo: jayk7/Getty Images
Silk preserves food through a combination of three factors which the caterpillars use during their metamorphosis. The silk cocoons keep water inside, so the caterpillars don’t desiccate, they minimize oxygen exchange from the outside, and they’re a barrier to microbes.
When applied to food, that means moisture is retained, metabolism is slowed — particularly important for living foods like fruits and vegetables — and microbial interactions are reduced.
“It doesn’t kill the bacteria, but not many of them have the right enzymes to break down silk, so it takes more time for them to break through the barrier,” Marelli said.
The amount of extra shelf life is dependent on variable conditions, depending on the specific type of food being coated, but silk can keep foods fresh and edible for days or weeks longer than untreated foods.
Official taste tests have not yet been conducted, but Marelli has tried the silk-coated food himself and noted no change to the eating experience.
“I once made silk in my own kitchen, it’s extremely simple to process, you just need a pot and some heat, and I didn’t taste anything. We need to do scientific studies with tasters, but my [own] experience is it doesn’t taste like much,” Marelli said.
Today, silk is harvested from caterpillars for the textile industry. That process requires killing the animals in order to preserve the cocoons so the silk can yield a single, long thread. For food preservation, that won’t be necessary.
Once the cocoon is produced, it’s broken down and returned to the state it was in inside the silk gland and processed into a water suspension of silk. From there, foods can either be sprayed or dip-coated with a thin layer of edible silk.
Other types of silk, like those produced by spiders, could also be used, though spider silk has a scaling problem. It can’t be manufactured at the same scale as caterpillar silk. In the future, scientists could cut the bugs out of the operation entirely, instead using micro-organisms to produce silk.
“At scale, when it comes to production and capillary synthesis of silk, a yeast or bacteria with a bioreactor would be the way to go. If we can simply have yeast or bacteria making the silk in different parts of the world, then we don’t have to ship it,” Marelli said.
That decrease in shipping is a big part of the overall project, which aims to decrease the impact of agriculture on the planet while putting more food into the hands of people. Enhanced food preservation could reduce food deserts in parts of the world which regularly experience shortages. In the rest of the world, where food scarcity isn’t an issue, silk coating offers an alternative to plastics.
The first commercialized food products preserved with silk are intended to hit store shelves sometime in 2022, meaning someday soon you could grab a piece of fruit from a cart and pop it straight into your mouth, silk coating and all.