The green, leafy vegetables stored on top exposed to light in markets have more vitamins than the packages underneath kept in the dark in stores or in your refrigerator. See the new study in the Journal of Agricultural and Food Chemistry published today, March 10, 2010, “Effect of Different Cooking Methods on Color, Phytochemical Concentration, and Antioxidant Capacity of Raw and Frozen Brassica Vegetables.” Imagine how much vitamins green leafy vegetables lose in your dark refrigerator if they’re kept there for a few days, after laying under a pile of other vegetables in the dark for more days in the supermarket.
Photosynthesis happens in continuous light whether your vegetables are wrapped and on a supermarket shelf, in your house, or still in the ground. Without photosynthesis, the vegetables lose their vitamins and other nutrients–fast.
When you walk down the aisles of a supermarket (or farmer’s market) look for the green vegetables such as spinach, kale, or collards that are exposed to the light on the shelf (or the sun) because those vegetables will have more vitamins than the vegetables beneath the top layer that are not exposed to light.
According to a March 5, 2010 New York Times article by Henry Fountain, “Greens Get a Boost Under the Glow of the Supermarket,” having supermarket light shining on the top layer of spinach is going to preserve the vitamins in the vegetables. The spinach or any other green vegetable lying under the top package or bunch not exposed to light is going to lose its nutrients and vitamins.
Check out the site of the Department of Agriculture’s Agricultural Research Service. For example, what’s in spinach that’s exposed to light? You’ll find in green vegetables such as spinach or lettuce and other green leafy vegetables–collards, kale, chard, arugula and other greens, vitamins A, B9, C and others are all related to photosynthesis.
Those vitamins and nutrients are synthesized in the plant when exposed to light, whether the plant is already picked and wrapped or in the ground. The top layer of green vegetable produce in the store is under continuous light.
When scientists tested for vitamin content two varieties of spinach, flat- and crinkle-leaf with simulated supermarket conditions — stored in clear sealed plastic at 39 degrees Fahrenheit under continuous fluorescent light — for up to nine days and compared those vegetables to similar produce leaves that had been kept in darkness, the vegetable leaves exposed to light had higher levels of all the vitamins except some from the vitamin A group.
If you try the experiment, you’ll see some wilting of the green leaves because water is broken down in photosynthesis. Retailers of vegetables should realize that the leaves on the bottom won’t be exposed to light and will lose vitamins faster. The way to fix the problem is to package leafy green vegetables in a way so that all the leaves would be exposed to light, perhaps in a shallow bag that’s transparent.
According to the abstract of the study, it evaluated the effect of common cooking practices (i.e., boiling, microwaving, and basket and oven steaming) on the phytochemical content (carotenoids, chlorophylls, glucosinolates, polyphenols, and ascorbic acid), total antioxidant capacity (TAC), and color changes of three generally consumed green, leafy vegetables, known as “Brassica” vegetables. The type of produce analyzed included fresh and frozen.
The study didn’t only look at vegetables kept in the light or in the dark. It also looked at cooking procedures, which is good information for chefs and parents. Among cooking procedures, the study found that boiling determined an increase of fresh broccoli carotenoids and fresh Brussels sprout polyphenols, whereas a decrease of almost all other phytochemicals in fresh and frozen samples was observed.
Steaming procedures determined a release of polyphenols in both fresh and frozen samples. Microwaving was the best cooking method for maintaining the color of both fresh and frozen vegetables and obtaining a good retention of glucosinolates.
During all cooking procedures, ascorbic acid was lost in great amount from all vegetables. Chlorophylls were more stable in frozen samples than in fresh ones, even though steaming methods were able to better preserve these compounds in fresh samples than other cooking methods applied. The overall results of the study demonstrated that fresh Brassica vegetables retain phytochemicals and TAC better than frozen samples.
So when you buy or grow your next batch of vegetables, be aware of how fresh vegetables compare to frozen ones, according to that study. Then make your own choice. Or read more studies comparing vegetables as to which has the most nutrition in what state–steamed, raw, or cooked in other ways. It’s notable that cholorophylls were more stable in the frozen samples than the fresh ones.
Steaming the vegetables preserved the compounds better in the fresh vegetables. With all these comparisons, perhaps, it’s time to juice the vegetables with their fiber in a powerful blender. Drink the emulsion, and try some of the green leafy vegetables fresh and raw. From a nutrition standpoint, maybe you’d like to try the juicing–with fiber.