US researchers boost fruit and vegetable shelf life with melatonin

Researchers at the Massachusetts Institute of Technology (MIT) in the US have developed a technique to extend the shelf life of fresh-cut fruit and vegetables by injecting them with melatonin using biodegradable microneedles. The method delays spoilage and reduces food waste, with the potential to offer an alternative or complement to refrigeration.

The team found that melatonin could 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 are wasted.

The FAO estimates that 30-40% of total food production is lost before it reaches the market, and around 14% of food produced is lost between harvest and retail.

The researchers used patches of silk microneedles that can penetrate the tough, waxy skin of plants without causing a stress response and deliver precise amounts of melatonin into their inner tissues. Melatonin is a hormone that helps humans sleep, and is naturally present in some plants to help them regulate growth and aging.

“This is the first time that we’ve been able to apply these microneedles to extend the shelf life of a fresh-cut crop,” says Benedetto Marelli, the study’s senior author, associate professor of civil and environmental engineering at MIT, and the 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.”

The findings, published in Nano Letters, could expand US access to healthy food in the future, he adds.

Tapping sleep hormone

To test the microneedle’s ability to extend the shelf life of food, the scientists studied the effect of melatonin on pak choy. 

“The dose of melatonin we’re delivering is so low that it’s fully metabolized 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,” explains Marelli. 

The researchers applied small patches of the melatonin-filled microneedles by hand to the bottom of pak choy plants (Image credit: Yangyang Han).“We chose pak choy because it’s a very important crop in Asia, and also because pak choy is very perishable.”

The researchers compared the shelf life of regular pak choy plants, and plants sprayed with or dipped into melatonin, finding no difference.

The team evaluated the plants by monitoring their weight, visual appearance, and concentration of chlorophyll, a green pigment that decreases as plants age. They estimated that 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,” says Marelli.

Eyeing agricultural advancement

In the future, the team expects the microneedle delivery technology to work with all kinds of produce, and offer waste reduction benefits over other application methods like spraying or dipping crops.

“We’re going to continue to analyze how we can increase the impact this can have on the value and quality of crops,” notes Marelli. He cites exploring the technology’s possibility of modulating the nutritional values, shape, and texture of crops. 

“We will also continue looking into scaling up the technology so this can be used in the field.”

However, for wide adoption, he acknowledges the need to reach a “performance versus cost threshold to justify its use.”

“This method would need to become cheap enough to be used by farmers regularly,” he concludes.