Antimicrobial spray could replace plastic wrap and reduce waste

In the fight against food waste, researchers have found a new solution: a tool that sprays fruits and vegetables with a thick web of antimicrobial threads, coating the surface and reducing spoilage by up to 50%.

This canvas, made of 100% biodegradable materials, could tackle more than just food waste by also replacing conventional fresh produce packaging, tackling pollution and emissions associated with the manufacture of petroleum-rich plastics that persist in nature.

The antimicrobial yarn was created and tested in research conducted by Harvard University, using a biopolymer called pullulan. This natural substance is made from starch, is considered food safe, and also forms a dense weave of fibers that provided the ideal base for the researchers’ 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 it to rot.

The next challenge was to find a way to deposit this antimicrobial substance on fresh produce. To do this, the researchers applied a technique called “focused rotary jet spinning”: it uses a machine to force the water-soluble pullulan mixture through a tiny opening, where it is rapidly heated so that at its out of the machine, it turns from a liquid into long threads that can be spun around the fruit. In this case, the test subjects were avocados, whose soft flesh is particularly vulnerable to rotting.

Once settled into the silk weave, the researchers left the avocados for seven days, during which time they hoped the antimicrobial mixture would work its magic and kill the pathogens on the fruit’s surface.

Antimicrobial product coatings are not a new idea, but most previous versions have not reduced microbes as effectively and have been expensive to produce. The researchers hoped that their new dense weave would increase the surface area of ​​antimicrobial activity, thereby applying a more potent dose to the product.

When they revisited their lawyers after a week, their hopes were confirmed. When cutting the avocados, they found that of the untreated fruit, 90% had started to rot, while this was only true for 50% of the avocados that had been woven into the antimicrobial web. This meant that the coating reduced the risk of rotting and spoilage by nearly half.

Meanwhile, tests on all fruit samples also showed coated avos had fewer surface microbes, were heavier – suggesting less flesh lost through degradation – and also greener and firmer than their counterparts.

It’s not just that the coating reduces food waste; it is also a practical invention. Because it is water soluble, the coating can be easily washed off products by consumers at home. Additionally, soil tests conducted by the researchers revealed that the coating degrades in just three days, compared to plastic packaging alternatives which can take centuries to degrade in the environment. The main ingredient pullulan can also be produced in a circular fashion, using starches derived from food waste, further reducing the footprint of the new material. And, its applications could go far beyond avocados to other fruits and vegetables, and perhaps even meat.

A potential downside is that it takes between two and four minutes to coat each fruit using this new method, which could make it less competitive in a packaging industry that thrives on speed and efficiency.

But, an added benefit of sprayable coating is that it is inexpensive to manufacture. The invention only costs a few extra pennies per item to apply, far less than the price of plastic packaging, when all the costly environmental externalities associated with plastic waste are taken into account. This expense will also decrease as the product evolves, which the researchers hope will follow next.

“We knew we had to get rid of the petroleum-based food packaging that exists and replace it with something more sustainable, biodegradable and non-toxic,” they say. Their invention brings us one step closer to that goal.

Demokritou & Parker et. al. “High-throughput coating with biodegradable antimicrobial pullulan fibers extends shelf life and reduces weight loss in an avocado model.” natural food. 2022.

Photo by Estúdio Bloom on Unsplash

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