21 June 2013

It's alive! Nutritional value of fresh produce varies with time of day

by Will Parker

The fruits and vegetables we buy in the grocery store are actually still alive, leading scientists to conclude that the way we store our produce (as well as the time of the day we cook it) has significant effects on its nutritional value. The study "Postharvest Circadian Entrainment Enhances Crop Pest Resistance and Phytochemical Cycling" by researchers at Rice University appears in the journal Current Biology.

For the study, the researchers investigated whether a variety of food crops would continue to exhibit physiological changes driven by circadian rhythms after they'd been harvested from the field. "Unlike animals, plants are made up of many separate components that can continue to metabolize and survive more or less independently, at least for some time. Even after they've been harvested and cut from one another, their cells remain active and alive," explained Janet Braam, who led the study.

Braam found that post-harvest vegetables and fruits can, in fact, continue to perceive light and, as a result, their biological clocks keep ticking. "That's an advantage to the plants because it allows them to alter levels of important chemicals that protect them from being eaten by insects and other herbivores," she said. "When eaten by us, some of those same phytochemicals also have anti-cancer effects."

The researchers made the initial discovery in studies of cabbage. They then went on to show similar responses in lettuce, spinach, zucchini, sweet potatoes, carrots, and blueberries.

Braam suggests it might be time to consider our foods' daily schedules - not just our own - when deciding what time to have dinner. "Vegetables and fruits, even after harvest, can respond to light signals and consequently change their biology in ways that may affect health value and insect resistance. Perhaps we should be storing our vegetables and fruits under light-dark cycles and timing when to cook and eat them to enhance their health value."

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Source: Current Biology