They’re Alive! Harvested Produce Still Respond to Light

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Fruits and vegetables on grocery store shelves may have left the farm but that doesn’t mean they’re inert.

It turns out cabbage, blueberries, spinach and carrots still respond to light about a week after being picked, and that means they continue to change their biology even as they sit in a store. We all know that harvested fruits can continue to ripen, and that fruits and vegetables can rot, but they also have other reactions to the light-dark cycle that can affect their nutritional content and even their ability to protect against pests.

Janet Braam of Rice Univeristy and her colleagues previously showed that fruits and vegetables change their physiology, and therefore their nutritional content, throughout the day based on circadian rhythms. The plants can also create natural defenses to pests during the day, for example, when they are saturated in light, since insects are most active at these times. So the team wanted to see if these processed continued after a fruit or vegetable is plucked from its home.

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They started with cabbage and found that when that plant was kept in a cycle of alternating 12 hours of light and 12 hours of dark, it continued to produce glucosinolate, a compound that shields it from being consumed by insects like caterpillars. They found the same results when they looked at other fruits and veggies including lettuce, spinach, zucchini, sweet potatoes, carrots and blueberries.

“This has some great potential to guide our thinking on how to manage pests better without such high-impact efforts as pesticide use,” Jerry Glover, an agricultural ecologist with the U.S. Agency for International Development, who was not involved in the study said to National Geographic.

According to the researchers, who reported their results in the journal Current Biology, these plants are able to “survive” even after harvest since they are made up of semi-independent parts like branches, roots and fruits that each have cells able to function on their own.

Braam’s team also found that these insect-fighting agents, some of which are phytochemicals, are also responsible for some of their anti-cancer and health-promoting effects when consumed by people. Harvesting produce at the wrong time, then, could lead to fruits and vegetables with less nutritional value. “It may be of interest to harvest crops and freeze or otherwise preserve them at specific times of day, when nutrients and valuable phytochemicals are at their peak,” said Braam in a statement.

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Pinpointing the peak of a fruit’s freshness, however, will require more research. And convincing growers to accommodate the plant’s circadian clock when harvesting could be an impossible task. But if such practices help the produce industry from losing so much of their inventory to unripened or rotting products, it might be worth considering. Fruit and vegetable lovers, for one, would welcome the change.