As summer arrives, the number of vegetables and fruits that quickly spoil and are thrown away increases. Scientists have developed a technique to store vegetables and fruits longer using the natural substance melatonin and the components from onion skins. Vegetables and fruits are usually stored for a longer time using cold chain distribution or by placing them in plastic bags. It is expected that the shelf life of vegetables and fruits can be extended without these processes, significantly reducing food waste.
◇Melatonin reduces wilted vegetables
Benedetto Marelli, a professor in the Department of Civil and Environmental Engineering at the Massachusetts Institute of Technology (MIT), and Sarojam Rajani, a researcher at the Temasek Life Sciences Laboratory in Singapore, reported the research results indicating that "melatonin can extend the shelf life of vegetables" in the international journal Nano Letters published by the American Chemical Society in May. Melatonin is a hormone that helps human sleep, but it has the effect of preventing plants from wilting.
The research team injected 22μg (micrograms; 1μg is one-millionth of a gram) of melatonin into freshly harvested bok choy using a microneedle patch. The microneedles were made of biodegradable silk, with a length of 70μm (micrometers; 1μm is one-millionth of a meter). As a result, the shelf life of bok choy increased by 4 days at room temperature of 25 degrees Celsius. When refrigerated, the shelf life extended by 10 days.
The research team also added melatonin to cabbage. Regular cabbage turned yellow by the second or third day and could not be sold by the fourth day. The cabbage treated with melatonin remained green on the fifth day and could be sold up to the eighth day. Melatonin was found to affect plant chlorophyll, slowing down the wilting process. The researchers noted, "Melatonin reduces plant stress," adding that "since only a small amount of melatonin is added to plants, the amount consumed by humans is negligible."
During the harvesting and distribution of vegetables, leaves can droop or wilt. The research team believes that vegetables can be kept fresh until they reach consumers' tables without using a cold chain. They stated, "This research was conducted manually," and suggested that using agricultural equipment, tractors, and autonomous drones could enable mass application of microneedles to vegetables.
◇Onion skin fibers extend orange shelf life
Poornima Vijayan, a professor in the Department of Chemistry at Sri Narayana College in India, noted that "the shelf life of fruits can be extended with cellulose nanofibers extracted from onion skins," in the international journal Hybrid Advances last April. Cellulose, a plant-based dietary fiber, is a polymer that constitutes the skin of plants. The research team produced cellulose at the nanometer scale (1nm is one-billionth of a meter).
The research team mixed cellulose nanofibers with polyvinyl alcohol (PVA), a water-soluble polymer, and curcumin, the yellow pigment from turmeric, to create a solution. Oranges were submerged in this solution for 2 minutes and then naturally dried. Usually, oranges have a shelf life of about 13 days, but the oranges coated with cellulose nanofibers were reported to retain freshness for a longer period.
Cellulose nanofibers are easily decomposed by heat in hot and humid regions like India. The research team discovered that PVA can combine the nanofibers, enhancing the waterproof and heat-resistant properties of the film. PVA is non-toxic and biodegradable. Nano-curcumin is a yellow pigment extracted from turmeric powder, which has antibacterial and antifungal properties.
Fruits and vegetables are essential foods containing vital vitamins, minerals, and other nutrients for a healthy diet. However, 20-30% of fresh produce is wasted due to over-ripening during storage after harvest. Typically, fruits are stored in plastic bags to keep them fresh. This can lead to environmental impacts since it does not decompose well in the ground. The research team stated, "By extending the shelf life of fruits with onion skins, which are agricultural waste, we can reduce the environmental pollution caused by food packaging."
References
Nano Letters (2025), DOI: https://doi.org/10.1021/acs.nanolett.5c00487
Hybrid Advances (2024), DOI: https://doi.org/10.1016/j.hybadv.2024.100162