Fruits and vegetables should not be stored in the fridge or a dark cupboard because they need a natural cycle of day and night to produce optimum levels of nutrients and flavour, scientists claim.
Because they remain alive after being picked, the biological clocks of fruits
and vegetables continue to tick meaning their cells remain active and they
are still sensitive to the time of day.
Allowing them to continue on a day-night cycle keeps them in a more natural
and healthy state while permanent darkness or light may affect their
nutrient content for the worse, researchers found.
Like plants, food crops use their 24-hour clock to change their physical state
throughout the day, for example by altering levels of chemicals which help
them ward off pests.
These chemical balances can have an important impact on taste and nutritional
value and some are even known to have anti-cancer properties.
The findings suggest that the way we store our food, and even the time of day
that we eat it, could profoundly alter how healthy it is for up to a week
after it is harvested, researchers claimed.
Janet Braam, professor of biochemistry and cell biology at Rice University in
Houston, Texas, explained: "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."
Writing in the Current Biology journal the researchers, from Rice University in Houston, Texas, described how the chemical balance of cabbage changes depending on how it is stored.
Using cabbage leaves that had been harvested two to three days earlier, the scientists exposed some samples to a 12-hour cycle of daylight and darkness for three days, while others were kept in permanent light or dark.
They found that those kept in a natural day-night cycle contained higher levels of key chemicals which repel pests, and they were gorged on half as much by insect larvae.
Some of these chemicals, known as glucosinates, can affect flavour and have been shown in other studies to have "potent" anti-cancer properties, the researchers said.
Levels of one such glucosinate, known as 4MSO, were also found to peak at certain points in the day.
A cabbage kept in natural light conditions and eaten four to eight hours after the first light would contain two to three times as much of the chemical as one kept in permanent darkness until eating, researchers said.
There was no significant difference between the cabbages after six or nine days, suggesting that their sensitivity to day and night lasts for only a week after harvest, or four to five days after purchase.
Refrigerating the cabbages did not prevent them regulating their chemical levels – but only if they still had a 12-hour period of light each day, meaning vegetables kept in a kitchen fridge may not fare so well.
Further tests revealed that lettuce, spinach, courgettes, sweet potatoes, carrots and blueberries all suffered less damage from pests when kept in a natural light-dark cycle, suggesting similar chemical processes could happen in various crops.
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"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."
Writing in the Current Biology journal the researchers, from Rice University in Houston, Texas, described how the chemical balance of cabbage changes depending on how it is stored.
Using cabbage leaves that had been harvested two to three days earlier, the scientists exposed some samples to a 12-hour cycle of daylight and darkness for three days, while others were kept in permanent light or dark.
They found that those kept in a natural day-night cycle contained higher levels of key chemicals which repel pests, and they were gorged on half as much by insect larvae.
Some of these chemicals, known as glucosinates, can affect flavour and have been shown in other studies to have "potent" anti-cancer properties, the researchers said.
Levels of one such glucosinate, known as 4MSO, were also found to peak at certain points in the day.
A cabbage kept in natural light conditions and eaten four to eight hours after the first light would contain two to three times as much of the chemical as one kept in permanent darkness until eating, researchers said.
There was no significant difference between the cabbages after six or nine days, suggesting that their sensitivity to day and night lasts for only a week after harvest, or four to five days after purchase.
Refrigerating the cabbages did not prevent them regulating their chemical levels – but only if they still had a 12-hour period of light each day, meaning vegetables kept in a kitchen fridge may not fare so well.
Further tests revealed that lettuce, spinach, courgettes, sweet potatoes, carrots and blueberries all suffered less damage from pests when kept in a natural light-dark cycle, suggesting similar chemical processes could happen in various crops.
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