Melatonin, the sleep-calibrating hormone, is a boon to long-distance travelers. Now, a research paper highlights another surprising application: melatonin could also be a vital tool to help fresh produce survive its own journey from farm to fork, reducing the monumental amount of food loss that occurs each year.
It might seem like an odd combination, but actually dozens of papers have investigated the potential of melatonin, a naturally-occurring plant hormone, to reduce ‘chilling injury’ in plants. This is a huge problem that occurs during refrigeration between the farms and the store where produce will be sold: while cooling is necessary—sometimes for weeks—to prevent spoilage, the trade-off is that lots of produce gets damaged or ‘injured’ by the chill, a process that breaks down cell membranes and causes their contents to leak out.
This causes uneven ripening across the fruit and veg, forming pockets where flesh browns, pits, and hardens—forming those unappetizingly soft or gristly bits that will be familiar to anyone who’s ever bitten into an artificially-ripened pear or plum.
The new research paper, published in Food Reviews International, is the first to draw together the evidence from almost 100 studies which had looked at the benefits of melatonin when smeared onto the surface of everything from apples to jackfruit, bananas to tomatoes.
What they found across the studies overall, is that melatonin reduced cold injury by as much as 21% and up to 42%, in dozens of types of fruit and vegetables. On average, fruit fared better with melatonin treatment than did vegetables, which remained more susceptible to the cold (though, chilling injury was still reduced in some vegetables such as bell peppers and cucumbers by up to 24%.)
The large variability reflected the variability of fresh produce itself, where different types of flesh and peels determine sensitivity to the cold. For instance, the analysis found that of the fruit types, oranges and peaches treated with melatonin showed fewer signs of chill injury than did kiwifruits, litchis, pomegranates and bananas.
Overall, melatonin treatment made for better quality fruit and vegetables, most of which were weightier and firmer—suggesting less damage—than produce tested in the controls.
Exactly how melatonin protects fresh produce against the ravages of cold isn’t something the research has fully illuminated yet. But there are clues. When melatonin is applied to the surface of fruits and vegetables, it seems to induce the production of more of this hormone inside the plants’ cells. Melatonin has receptors linked to many cellular functions in plants, and among other things it seems that some of these amp antioxidant activities, which help to scavenge free radicals and stave off damage and decay.
An added benefit of this hormone is that compared to some of the fumigants and chemicals that are currently applied to preserve food, melatonin is safer to use and consume, the researchers say. Most importantly, by increasing the tolerance to chilling, it could make a significant dent in the monumental amount of food that’s lost to damage each year. One-third of all food is either lost or wasted annually, and fruit and vegetables account for the largest share of that: 31.5% of it all goes uneaten each year.
According to separate research, reducing food loss and waste isn’t necessarily the panacea we previously believed it was. But it’s still an important action to take for the environment and for human nutrition and health. As the new study’s researchers say, “This is a crisis affecting nations all over the world, so we need to find the solution to keep producing food from the earth in a sustainable way.”
Shah et. al. “Insight into the Role of Melatonin in Mitigating Chilling Injury and Maintaining the Quality of Cold-Stored Fruits and Vegetables.” Food Reviews International. 2023.