In the fight against food waste, researchers have come up with a new solution: a device that sprays fruits and vegetables with a thick web of antimicrobial threads, coating the surface and reducing spoilage by nearly 50%.
This web, made from 100% biodegradable materials, can tackle more than just food waste by replacing traditional packaging on fresh producecombats the pollution and emissions associated with making petroleum-heavy plastics that are made in nature.
In research led by Harvard University, an antimicrobial thread was created and tested using a biopolymer called pullulan. This naturally occurring substance is made from starch, is considered safe for use on food products, and also forms a dense weave of fibers that provides an ideal basis for researchers to experiment. Using pullulan as a vehicle, researchers infused it with naturally antimicrobial ingredients including thyme oil and citric acid, which can fight pathogens such as e coli that infect food and cause rotting,
The next challenge was to find a way to deposit this antimicrobial substance on fresh produce. To this end, the researchers applied a technique called ‘focused rotary jet spinning’: it uses a machine to force a water-soluble pullulan mixture through a small opening, where it is rapidly heated. So that as soon as it exits the machine, it is replaced by one. Liquid in long threads that can be spun around the fruit. In this case, the test subjects were avocados, whose soft flesh is particularly vulnerable to rot.
After joining the silky weave, the researchers left the avocados in place for seven days, during which time they hoped the antimicrobial mixture would work its magic and zap pathogens onto the fruit’s surface.
Antimicrobial product coatings are not a new idea, but most previous versions have not reduced microbes so effectively, and have become expensive to produce. The researchers hoped that their new, dense weave would increase the surface area for antimicrobial activity, therefore applying more potent doses to yield.
When he revisited his avocados after a week, his hopes were confirmed. Slicing into avos, they found that 90% of the untreated fruit had rotted awaywhereas this was only true of 50% of avos that were woven into the antimicrobial web. This meant that the coating cut the chances of rot and waste by almost half.
Meanwhile, tests of all the fruit samples also showed that the coated avos had fewer surface microbes, were heavier suggesting that less flesh is lost to degradation and greener than their counterparts. And stronger too.
It’s not just that the coating reduces food waste; This is also a practical invention. Since it is water soluble, the product can be easily washed off by consumers at home. What’s more, soil tests conducted by the researchers showed that the coating degrades in just three days as compared to plastic packaging options, which can take centuries to break down in the environment. The main pullulan ingredient can also be produced in a circular fashion using starch obtained from food waste, further reducing the footprint of the new material. And, its applications may extend far beyond avocados to other fruits and vegetables, and perhaps even meat.
One potential setback is that it takes two to four minutes to coat each item of fruit using this new method, which could make it less competitive in a packaging industry that thrives on speed and efficiency.
But, an added boon of sprayable coating is that it is cheap to make. It only costs a few extra cents per item to implement the invention, much cheaper than the cost of plastic packaging, when you take into account all the costly environmental externalities associated with plastic waste. As the product grows, that expense will also come down, which the researchers expect going forward.
“We knew we needed to get rid of petroleum-based food packaging and replace it with something more sustainable, biodegradable and non-toxic,” he says. His invention brings us one step closer to that goal.
Democritou and Parker et. al. “High-throughput coating with biodegradable antimicrobial pullulan fibers extends shelf life and reduces weight loss in an avocado model.” nature food, 2022.
Unsplash. Photo by Per Estudio Bloom
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