Fruits and vegetables know the time of day

Fruits and vegetables are still alive, even after harvesting, and respond to cycles of day and night, according to new research published in the journal Current Biology. This is the first time that circadian rhythms have been recorded in harvested food products.

Being able to predict when foods will be in day or night mode could help food producers to harvest and store foods at the best time of days to benefit taste or nutrition. It may also change the way we store foods in our homes.

"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," Janet Braam of Rice University, one of the authors of the study, said.

When exposed to light, these fruits and vegetables change their levels of certain natural herbicides and pesticides, to protect them from insects and other pests. This behavior after harvest indicates that the biological clocks within the fruits and vegetables are still ticking, something that could only occur of the foods were still living.

"[Plants] know when the insects eat, so they can prepare a defense in advance," Braam said.

Braam and her team bought cabbage at a grocery store, then cut two-inch samples from the leaves. They then trained the leaves to a light cycle of 12 hours of day, followed by the same length night. After three days, Braam and her team measured the levels of the glucosinolates produced, and were able to determine the levels still responded to day/night cycles.

Although this discovery was first noticed in cabbage, the research team discovered that the same behavior happening in harvested specimens of spinach, zucchini, sweet potatoes, carrots and blueberries. These species do not have glucosinolates, but do have other natural chemicals to fight off pests which were active after harvest.

Some of the phytochemicals released by sunlight have been suggested to have benefits in preventing cancer. Being able to time when these chemicals are at their peak could prove to be helpful for personal nutrition.

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