MIT researchers gave freshly cut pak choy melatonin through tiny needles; the vegetables stayed saleable for 4 extra days at room temperature without refrigeration

The quality of vegetables starts declining as soon as they are harvested. Every extra day before leaves wilt or turn yellow can mean the difference between food being eaten and food being thrown away. Although one might suggest that refrigeration could be a key to extending the life of vegetables, it requires a lot of devices, resources, and transport means that are not always available. Researchers from MIT, therefore, developed a method to slow the aging process of harvested vegetables by using a small dose of a natural plant hormone right after harvesting. According to a study published in Nano Letters and described by MIT, experiments with freshly cut pak choy showed that vegetables treated with microscopic biodegradable needles carrying melatonin remained saleable for four extra days at room temperature without refrigeration.

A new way to protect freshly harvested produce

The researchers worked on the concept of making little patches that could attach to the vegetable without the need to spray or soak them with any liquid. The patches were made with silk fibroin, which is a natural protein extracted from silk. The patches had a number of tiny needles of 700 micrometers in length, which were not sufficient to harm the vegetable upon contact, but they penetrated deep enough to reach inside the vegetable tissues.


The team attached the patches to the freshly cut base of pak choy, where water and nutrients normally move through the plant. The microneedles delivered a very small amount of melatonin directly into the vegetable's vascular system. Melatonin is widely known as a hormone involved in human sleep, but plants also naturally produce it. However, whereas in humans melatonin has its main role in regulating sleep, in plants it is responsible for the growth and aging process, so the researchers supplied the plant with a small dose of the hormone, which was then metabolized by the pak choy.

Why just surface treatments failed

The researchers initially tested simpler methods. They sprayed pak choy with melatonin and also steeped the vegetables in a solution containing melatonin. The results of both methods showed no difference regarding the shelf life of the vegetables. Thus, it is evident that microneedles mattered. Instead of leaving the hormone on the plant's surface, the needles inserted the hormone directly into the plant's internal transport system, where it could circulate throughout the whole vegetable.

How to keep the leaves green for longer

In order to evaluate the effectiveness of treatment, scientists tracked several signs of aging in pak choy, including leaf color, chlorophyll content, and dehydration. It was discovered that normal pak choy took no more than two to three days to wilt at room temperature. By the fourth day, pak choy had deteriorated so much that it might have already lost its marketability. In comparison with untreated pak choy, the treated vegetables followed a different pattern. Treated pak choy was greener for longer, dehydrated more slowly, and had higher levels of chlorophyll. Scientists concluded that treated pak choy remained fit for consumption for about eight days. It was approximately four days longer than untreated pak choy that was kept at room temperature. When refrigerated, treated pak choy also showed a longer storage life than untreated pak choy.

How melatonin changed the plant’s response

The researchers found that the injected melatonin triggered protective responses inside the harvested plants rather than simply coating or preserving the leaves. Gene analyses showed that the hormone influenced pathways involved in antioxidants, chlorophyll preservation, and plant aging, helping the cut vegetables cope with the stress of being harvested. Moreover, the small amount of melatonin used did not dramatically enhance the vegetable's natural melatonin level, as it was metabolized during the process. The MIT team states that around 30 percent of all food is spoiled after harvest, which is enough to feed over 1 billion people. The spoilage of food happens before the food reaches the consumer since fresh food products deteriorate due to the long storage and transportation processes.

The future challenge of scaling freshness technology

Fresh leafy vegetables are especially difficult to preserve because they lose water quickly and deteriorate rapidly without controlled storage. The importance of technologies like silk microneedles is that they target the plant’s own aging process rather than only changing storage conditions. In the MIT experiment, the melatonin dose was approximately 22 micrograms, and the added hormone did not significantly change the natural melatonin level of the harvested vegetable because the plant metabolized it. The next challenge is scaling such methods out of the lab. Something that could be applicable to the individual vegetable would need to be transformed into a technology suitable for large-scale farms, packing houses, and transportation systems that deal with large quantities of products every day.