Injectable tech for fresh produce could extend shelf life

In Australia around 3 million tonnes of fruit and vegetables are wasted every year, with around 22% of that wastage occurring at the post-harvest stage of processing.

Researchers from Massachusetts Institute of Technology (MIT) and the Singapore-MIT Alliance for Research and Technology (SMART) have now developed a technology that could help to extend the shelf life of harvested plants by injecting them with melatonin using biodegradable microneedles.

The researchers believe their system could offer an alternative or complement to refrigeration for post-harvest fresh produce. The system uses patches of silk microneedles that are designed to penetrate the tough, waxy skin of plants without causing a stress response, while delivering a specific amount of melatonin into plants’ inner tissues.

“This is the first time that we’ve been able to apply these microneedles to extend the shelf life of a fresh-cut crop,” said senior author Benedetto Marelli, an associate professor of civil and environmental engineering at MIT and Director of the Wild Cards mission of the MIT Climate Project. “We thought we could use this technology to deliver something that could regulate or control the plant’s post-harvest physiology. Eventually, we looked at hormones, and melatonin is already used by plants to regulate such functions.”

Published in Nano Letters, the study explains how the small patches of the microneedles containing melatonin are applied to the base of the leafy vegetable pak choy. After application, the researchers found the melatonin was able to extend the vegetables’ shelf life by four days at room temperature and 10 days when refrigerated, which could allow more crops to reach consumers before they’re wasted.

Image credit: Yangyang Han; MIT News.

“The dose of melatonin we’re delivering is so low that it’s fully metabolised by the crops, so it would not significantly increase the amount of melatonin normally present in the food; we would not ingest more melatonin than usual,” Marelli said. “We chose pak choy because it’s a very important crop in Asia, and also because pak choy is very perishable.”

The team evaluated the plants by monitoring their weight, visual appearance and concentration of chlorophyll — a green pigment that decreases as plants age. At room temperature, the leaves of the untreated control group began yellowing within two or three days. By the fourth day, the yellowing accelerated to the point that the plants likely could not be sold. Plants treated with the melatonin-loaded silk microneedles, by contrast, remained green on day five, and the yellowing process was significantly delayed. The weight loss and chlorophyll reduction of treated plants also slowed significantly at room temperature. Overall, the researchers estimated the microneedle-treated plants retained their saleable value until the eighth day.

“We clearly saw we could enhance the shelf life of pak choy without the cold chain,” Marelli said.

In refrigerated conditions, plant yellowing was delayed by about five days on average, with treated plants remaining relatively green until day 25.

While the microneedles could make it possible to minimise waste when compared to other application methods like spraying or dipping crops, the researchers say more work is needed to deploy microneedles at scale. The research team also plans to study the effects of the technique on other types of produce.

Top image credit: iStock.com/stuartpitkin