Vegetables Get Jet Lag, Too

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.

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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.

Other Things You Can Do To Maximize The Nutrition From Fresh Produce

There are also things consumers can do to maximize nutrient value, particularly antioxidant content, of fresh produce during preparation.

• Rip salad greens into bite-size pieces several hours before serving. Rinse them in room temperature tap water, dry them in a salad spinner, and let them sit on the counter in a well-lit kitchen until you are ready to prepare the meal. The leaves will triple or even quadruple their antioxidant content to prevent bacterial infection through the torn tissue, and you can benefit from that increased antioxidant content by eating the salad greens raw.
• When you chop vegetables, use a sharp knife, not a dull knife. A dull knife crushes cells in the plant, allowing electrolytes such as potassium and minerals such as magnesium to leak away. Chopping vegetables or slicing fruit with a sharp knife increases available mineral content,.

• Shredded vegetables are more prone to discoloration and decay than than torn or chopped vegetables. Sometimes, however, shedding vegetables is preferable, especially when you plan to ferment them or to marinate them.
• Marinating or fermenting vegetables prevents nutrient loss if you consume the liquid in which they are prepared.
• The more finely you chop vegetables, the more quickly you should consume them. Fine-chopped vegetables should be consumed within one hour of preparation. "Smothering" the vegetable in mayonnaise-based salad dressings, however, also greatly slows down the growth of oxygen-dependent bacterial decay organisms.
• Bacteria such as E. coli and Listeria innocua are less likely to be present on intact vegetables than on vegetables prepared (chopped or shredded) at a factory. You should slice, dice, chop, and shred vegetables only after you get them home.
• White edges on carrots are usually due to dehydration. Storing carrots in a cellar or a crisper also helps preserve their color.
• Vegetables and fruit dried at low temperatures usually have much higher antioxidant content than their fresh counterparts. Dried carrots, for example, contain four times as much beta-carotene as equivalent weights of fresh carrots, and dried tomatoes contain nearly 10 times as much lycopene as fresh tomatoes.
• Canned vegetables don't always have lower nutrient content. The group of nutrients that the body can convert into vitamin A or use in ways similar to the way it uses vitamin A (alpha-carotene, beta-carotene, gamma-carotene, lycopene, lutein, and zeaxanthin) are more concentrated in canned vegetables than in fresh vegetables, but more concentrated in dried vegetables than in canned vegetables.

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• Steamed vegetables usually have higher nutrient concentrations than boiled vegetables, although boiled starches are usually more nutritious than steamed starches. Potatoes and white rice that are "boiled to death" form resistant starch, which resists conversion into sugar, but feeds probiotic bacteria in the colon. (Brown rice, however, is more nutritious steamed than parboiled.)

The ways you store and prepare vegetables can make a huge difference in their available nutritional content. Remember, the more "natural" the experience is for your food, the more closely it is kept in conditions that resemble those in which it was grown, and the sooner you consume the food after purchasing it, the more it supports your health.