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Want to maximize the nutritional content of your leafy greens? Then don't store them in the refrigerator, a study published in the journal Current Biology advises.
Danielle Goodspeed, a graduate student at Rice University in Houston, Texas, notes that the best vegetables you can buy at the grocery store are still alive. They can stay alive for days or even weeks as long as they get daily exposure to light, producing vitamins and antioxidants as they continue to grow. That head of lettuce or bunch of kale you buy at the store does not actually die until it has been held in the dark for a full three days.
Vegetable Jet Lag
Goodspeed says that nutrient and antioxidant production in vegetables such as cabbage, lettuce, and spinach is disrupted when the still-living plant is put in storage in the dark. While they are still growing in the field, these vegetables make antioxidants every morning to protect themselves against insect pests. Gnawing, chewing, and biting insects still damage the plant, but they do not cause the kind of tissue injury that invites infection with molds and bacteria when antioxidant levels are high. Neither do the leaves of plants turn brown or purple with mechanical injury.
In a series of experiments, Goodspeed and her collaborators put groups of vegetables on a 12-hour light and darkness schedule, and put corresponding groups of vegetables in total darkness. After 72 hours they then exposed both groups of vegetables to hordes of a hungry insect known as cabbage loopers.
After the three-day treatment, the bugs ate half as much of the vegetables that had been exposed to the light as the vegetables that had been held in darkness. The bugs on the veggies that were stored in the dark grew twice as large as their buddies who fed on plants that had been stored in light 12 hours out of every 24.
Plants Make Phytochemicals On a Regular Schedule
The Rice University researchers then analyzed the remaining plant matter for nutritional phytochemicals. They found that the plants that had been exposed to light had made two to three times as much of the plant-protective and human health-protective chemicals as the plants that had been stuck in the refrigerator.
Although reducing insect damage is not a major consideration once a vegetable is already in the warehouse or grocery store waiting to be bought by consumers, lighting in warehouses and storerooms could have many applications in shipping, preparation, and consumption of fresh produce, and the freshness of produce when it is bought and when it is consumed.
In scientific terms, sticking veggies in the refrigerator induces a circadian rhythm disorder. Storing them in a cool place on the counter, even putting greens in water as if they were cut flowers, helps them maintain the normal biorhythms that help them fight microorganisms that cause decay. Not only will veggies taste better if they are treated more like flowers than like dead foodstuffs, they will also be more nutritious and last longer between shopping trips.