Food Lasts 1 Week Longer with this Edible Silk Coating

Dip-coating a strawberry in a silk fibroin suspension to extend its shelf life.

Mori’s silk protein coating for food promises to also reduce the global waste stream and cut down on plastic packaging.

What’s up with Italians and silk? No substance seems more synonymous with Versace or any of Italy’s elegant fashion houses than silk—it’s the bedrock upon which the high-couture brands of Rome and Milan are built. Now, a Boston-based Italian scientist named Benedetto Marelli has launched a biotech startup called Mori to utilize silk proteins for dressing up garden vegetables, tenderized steaks, fresh poultry, and other forms of perishable and packaged foods. 

Marelli isn’t aiming for more fashionable packaging. Instead, he wants to extend the shelf life of fresh and packaged foods, prevent bacterial contamination and oxidative spoilage, and spare people from food poisoning. He got the idea to use silk proteins from looking at the building of the Italian Silk Institute—a trade organization that promotes the fabric and its uses. He used to walk by it on his way to class while an undergraduate at Milan’s Polytechnic University.

Now an assistant professor at MIT, Marelli has devised an eco-friendly process to extract and repurpose one of the waste products of the silk industry: an edible protein called fibroin, which is found in silk fibers. Fibroin as a chemical is amphiprotic, which means it can both accept or donate a proton and thus act as an acid or a base in an aqueous solution, either releasing one of its own a hydrogen ions (H+) or attaching a chemical known as a hydroxyl group (OH-). That means the protein can eventually be turned into a colorless liquid that can be applied to almost any food—from fruit to meat to vegetables—and in doing so, extend its viability a week on average at room temperature. 

Silk is composed mainly (78 percent) of two proteins, sericin, and fibroin. Fibroin is the structural center of the silk fiber, and sericin is the adhesive material surrounding it. Silk fibroin proteins naturally self-assemble into a flat layer of rows of antiparallel strands of fibrils (a fibroin is composed of several fibrils) connected by a backbone of hydrogen bonds and whose amino acids are oriented in the opposite direction. A molecular arrangement known as a β sheet, this presentation accounts for the protein’s unique ability to interact with both acidic and basic solvents. Once processed in the lab and “hydrolyzed” to separate the protein strands from one another, these can be reassembled and easily arranged into high-performance multifunctional nanostructured films or gels.

“We then purify the gel obtained, which is similar to the liquid found in the caterpillar’s glands, and turn it into a nanostructure,” Marelli says.

Marelli’s proprietary process for extracting and purifying fibroin using only salt, water, and heat has recently helped his company, Mori, secure some $50 million in series B financing from a team of climate tech, food tech, and health and wellness investors. Marelli’s work was also recently recognized with a BioInnovation Institute & Science Prize for Innovation award, established by the editors of Science to recognize researchers who apply a solid scientific approach and an innovative and entrepreneurial strategy to find solutions to some of the world’s most fundamental social and environmental problems.

Solving our food spoilage problem is urgent.

When dispersed as a liquid over the surface of a kale leaf or even a fruit like a banana or a strawberry, the nanomaterial obtained solidifies into a flexible coating that seals the product away from contamination and oxidation. As a result, it can be used as a substitute for synthetic preservatives, like chemicals that retard the growth of fungi or mold.

And with rapidly rising food prices, an increase in global hunger, and ongoing population growth, solving our food spoilage problem is urgent. 

Scanning electron micrograph of silk fibroin. Eye of Science / Science Source

Massive amounts of waste

By some estimates, over 40 percent of freshly packaged foods and produce farmed worldwide ends up in the dumpster even as more than 800 million people worldwide are undernourished. Extending the shelf life of the world’s food supply at room temperature just for one week would be a boon for the agriculture and the food manufacturing industries and would significantly reduce the size of the global waste stream, since 30 percent of food goes uneaten at the retail and consumer level. 

Then there is the garbage patch of trillions of pieces of discarded non-biodegradable plastic food packaging floating in the Pacific. Substituting that plastic packaging with a natural, nontoxic, edible liquid that doesn’t modify the foods’ sensory appeal would significantly resolve the plastic choke in which the planet is caught. And reducing plastic would reduce greenhouse gas emissions as well, since over one-third of global greenhouse gas emissions are tied to how we produce, process, and package food, according to an UN-backed study.

“Ben’s application is significant way beyond the property of fibroin,” says Fiorenzo Omenetto, Dean of Research at Tufts University’s School of Engineering and Marelli’s former postdoctoral advisor. “It represents the first use of the protein at industry scale for food applications. But, even before that, Marelli’s research could be a game changer for agriculture in general; it can give rise to a library of technologies in the plant world that can protect seeds and crops and augment their yield and fruition while ameliorating environmental conditions, reducing the use of pesticides, water, and fossil fuels.” 

“An edible coating has been a ‘holy grail’ project in the food industry for a long time.”

And not only that, but Marelli’s innovation can also save lives and improve the economy. In 2020 alone, spoiled and contaminated foods caused more than 48 million cases of foodborne illness in the United States. Of these cases, 128,000 resulted in hospitalization, and 3,000 people died. Furthermore, according to the U.S. Food and Drug Administration (FDA), food poisoning adds a $15 billion burden to the U.S. economy every year.

“An edible coating has been a ‘holy grail’ project in the food industry for a long [time],” says Tony DeLio. A chemical engineer and executive director at New
York-based private equity fund MidOcean Partners, DeLio previously oversaw food manufacturing innovations for food behemoths such as Mars and Archer Daniels Midland. He says tackling the “shelf-life issue” has been a lifelong struggle. “Mori’s silk is interesting in that it also appears to inhibit mold,” he says.

Silk, of course, has a long history of uses in medicine. And though other research projects involving silk are being carried out with sustainable aims to replace petroleum-based materials for pharmaceutical applications, biocompatible optics, biodegradable substrate, and even regeneration and improvement of brain functions, Marelli’s application is the first to leverage silk’s fibroin natural properties to secure the food supply chain, both as a protective food coating and as a crop booster. “[A] solution that provides an extension to the usefulness of foods, reduces the waste stream and the reliance on plastic for industrial products like the one proposed by Marelli is just what is needed for the development of a cyclical economy,” says Jake Hebert, a spokesperson for One Step Closer to Organic and Sustainable Community (OSC²), an advocacy group formed by 40 U.S. natural product companies to advance sustainability in packaging and preservation. “The Marelli case is even more emblematic since the solution keeps close to what nature has already provided.”

Go Deeper