Leafy vegetables spoil very quickly. The same is true for several fruits and other vegetables. About 30 percent of them are wasted while in storage or during transportation because they need to be kept cold to slow down their deterioration. This can be expensive and not always available. Spoiled produce also contribute to food waste.
A team of scientists from the Massachusetts Institute of Technology and the Singapore-MIT Alliance for Research and Technology headed by Benedetto Marelli, an associate professor of civil and environmental engineering at MIT investigated how melatonin can keep fruits and vegetables fresh much longer through better administration.
Extending Shelf Life Without Refrigeration: How Injecting Melatonin Using Microneedles Helps Keep Fruits and Vegetables Fresh Much Longer
Role of Melatonin in Plants
Melatonin is a naturally occurring hormone produced in the pineal gland in the brain best known for regulating sleep-wake cycles or circadian rhythm in both animals and humans. It is also present in plants where it plays very different roles. It specifically functions as a multifaceted signaling molecule which contributes to their growth, development, and stress response.
Several studies have noted that melatonin delays plant senescence or aging. It also acts as a natural antioxidant that protects plant cells from oxidative stress caused by external factors like extreme temperatures and mechanical damage. It interacts with other plant hormones to influence other processes like cell division, root development, and defense or immune response.
Nevertheless, based on the above, the multi-disciplinary team of Marelli developed a more precise method of delivering melatonin to harvested produces. They came up with a biodegradable silk microneedles capable of delivering physiological doses of melatonin directly into plant tissue without causing harm. Their study tested this technology on pak choy.
Findings
Pak choy or bok choy is a fast-wilting leafy vegetable. It is an excellent candidate for testing the aforesaid melatonin delivery mechanism. Tests showed that melatonin-treated pak choy lasted 4 days longer than untreated pak choy at room temperature of 24 degrees Celsius. Treated pak choy also stayed fresh for up to 25 days under refrigeration or 4 degrees Celsius.
The developed silk microneedles, measuring about 700 micrometers, penetrated the surface of the plant without causing stress. Alternative methods like sprays and dips failed to deliver effective results. Microneedle delivery was the only mechanism that improved shelf life.
It is also worth mentioning that the team administered a very small dose of melatonin around 22 micrograms. This was enough to be fully absorbed and metabolized by the harvested plant and not too much to significantly alter the natural melatonin levels in the food.
Transcriptome analysis showed melatonin triggered antioxidant pathways that protect cells from damage, regulation of chlorophyll degradation which helped leaves stay green, and modulation of auxin synthesis. Auxin is a hormone linked to plant growth and aging. It also helped the harvested plant cope with both the biological and mechanical stress after being cut.
Applications and Implications
The process used by Marelli et al. was manual and labor-intensive. The researchers are working on scaling the method using machines, drones, or tractors to make it applicable in commercial food production. They are also exploring other plant hormones and crops to further improve postharvest quality, nutritional value, and even texture using the same delivery mechanism.
Remember that post-harvest lost account for over 30 percent global food waste. This is equates to about 1.3 billion tons of food. Extending the shelf life of important agricultural products even by few days can help in promoting food security. The process described above can help feed more people by preserving fruits and vegetables that would otherwise spoil quickly.
It is also worth noting that cold storage is expensive and energy-intensive. Most developing regions like Africa and Southeast Asia lack reliable cold chain infrastructure for refrigeration. The entire process developed by Marelli and his team and further advancements offer a low-impact and low-cost alternative to preserve fresh agricultural produce during transport and storage.
FURTHER READING AND REFERENCE
- Han, Y., Jangir, M., Ngoh, A. S. Y., Li, C., Sarangapani, S., Cao, Y., Zhang, Y., Cheerlavancha, R., Sarojam, R., and Marelli, B. 2025. “Precise Delivery of Physiological Doses of Melatonin in Planta to Control Postharvest Physiology and Extend Shelf Life Outside the Cold Chain.” Nano Letters. DOI: 1021/acs.nanolett.5c00487