Kale: The Phytonutrient Master
by Emily Skelton

Phytonutrients are health promoting plant compounds found in vegetables such as broccoli, spinach, and most of all, kale. The latest research shows that, of all the vegetables, kale has the highest concentrations of phytonutrients, especially the carotenoid phytonutrients, lutein and zeaxanthin. At the University of New Hampshire (UNH), two professors from two different disciplines are working together to find out what these nutrients mean to our fight against macular degeneration and cataracts¹. Kale also contains other phytonutrients like sulfur-containing compounds called glucosinolates. These glucosinolates have been found to raise levels of certain cancer-fighting enzymes in our bodies².

There are so many great ways to eat kale, from raw to cooked, in tasty soups or in salads, and kale is easy to grow in our own gardens. We should be eating this phytonutrient master every day! Read on and find out where kale originated, how to grow kale, how to prepare a delicious recipe using kale, and how it can improve your health.

History of Kale
Kale is a descendent of the wild cabbage, a plant thought to have originated in Asia Minor and to have been brought to Europe around 600 BC by Celtic travelers³. This wild cabbage is considered a native to coastal southern and western Europe, where its tolerance of salt and lime, but intolerance of competition from other plants, restricts its growing area to limestone sea cliffs⁴. Kale was a popular vegetable in Europe during the Middle Ages. English settlers brought kale to the United States in the 17th century.

Kale is a member of the cruciferae family of plants that includes broccoli, cauliflower, cabbage, and Brussels sprouts. There are two kinds of kale, Brassica napus and Brassica oleraceae. Brassica napus includes the Pabularia group known as Siberian Kale or Red Russian Kale. Brassica oleraceae includes the Acephala group also known as collards and Dinosaur Kale. Dinosaur kale is a much more recent variety. It was discovered in Italy in the late 19th century.

Carotenoids in Kale
At UNH, Dr. Dean Kopsell, Assistant Professor of Plant Biology, and Dr. Joanne Curran-Celentano, Associate Professor of Animal and Nutritional Sciences, are collaborating on the Carotenoid Project. They have a grant from the USDA to study the role of carotenoids in human health.

In Curran-Celentano's project, they are looking at how well humans take up lutein and deposit it in the macula lutea of their eyes. The macula lutea is the region of highest visual acuity in the eye. "Among all the vegetables, kale ranks highest in its concentration of the xanthophyll carotenoids lutein and zeaxanthin, the yellow-orange pigments plants evolved to help protect their tissues against the harmful effects of excess solar radiation."⁵ Lutein and zeaxanthin are like sunscreen for the plant's leaves. It is believed that these two carotenoids have the same protective properties on the human eye. When concentrated in the macula lutea they can absorb and disperse ultraviolet radiation to help protect against cataracts and macular degeneration. Curran-Celentano also verified that eating a variety of vegetables with high amounts of carotenoids, such as kale, is more beneficial than taking the same carotenoids in a supplement form.

Kopsell and his team have examined the genetic, cultural, and environmental factors that maximize the concentration of carotenoids in leafy greens. The team analyzed dozens of kale varieties. They found three varieties had two and a half times the carotenoid levels of the rest of the varieties. One of those varieties is the Dinosaur or Lacinato Blue Kale (Brassica oleraceae).

Glucosinolates in Kale
Kale contains a variety of glucosinolates which, when broken down by the body, form different isothiocyanates. Isothiocyanates and their metabolites have been found to inhibit the development of chemically induced cancers of the lung, liver, esophagus, stomach, small intestine, colon, and mammary gland in a variety of animal models⁶. Sulforaphane, an isothiocyanate, may help prevent cancer by promoting the elimination of potential carcinogens from the body and enhancing the transcription of tumor suppressor proteins. When kale is chopped or chewed, myrosinase, a class of enzyme, begins to interact with the glucosinolates and release the isothiocyanates. This increases the amount absorbed by the body. However, the absorption of isothiocyanates is substantially lower from cooked than from raw kale. Glucosinolates are water-soluble compounds that may be leached into cooking water. Boiling kale from 9–15 minutes can result in an 18–59% decrease in the total glucosinolate content. Cooking methods that use less water, such as steaming or sautéing may reduce glucosinolate losses (see recipe below). Several studies have found that inactivation of myrosinase in cruciferous vegetables substantially decreases the bioavailability of isothiocyanates⁷. Cooking at high heat may also decrease the activity of plant based myrosinase, but our gastrointestinal tract also has myrosinase, and still may be able to break down the glucosinolates.

Vitamins in Kale
When choosing the most nutritious varieties of kale, pick the deepest colors, as these will most often have higher contents of vitamins and carotenoids. Dinosaur Kale is a good example of a very dark-green kale. Pick fresh leaves from your garden and eat them within a few days, because the longer kale is kept the more the flavor declines. Keep the leaves in cool water or in the refrigerator, as kale kept in warm temperatures for too long will wilt and lose its flavor and the nutrients will begin to deteriorate.

Kale with Cannellini Beans From Vegetarian Cooking for Everyone by Deborah Madison Serves 2 to 4 Ingredients 1 1/2 to 2 pounds kale or mixed greens, stems and ribs removed Salt and freshly milled pepper 1 small onion, finely diced 1 1/2 tablespoons olive oil 2 plump garlic cloves, minced Pinch red pepper flakes 2 teaspoons chopped rosemary 1/2 cup dry white wine 1 1/3 cups cooked cannellini beans Freshly grated parmesan, optional Simmer the kale using 1 quart of water in a large cast iron skillet, bring to a boil, and add 1-teaspoon salt and greens. Simmer, uncovered turning the leaves until all are tender, 7 to 10 minutes. Drain. Save the nutrient-rich liquid for stock. Chop the leaves. In a large skillet, sauté the onion in the oil with the garlic, pepper flakes, and rosemary for about 3 minutes. Add the wine and cook until it's reduced to a syrupy sauce. Add the beans, kale, and enough cooking water (kale stock) to keep the mixture loose. Heat through, taste for salt and season with pepper, and serve with a dusting of parmesan. Serve with, or over, garlic-rubbed croutons or top with breadcrumbs crisped in olive oil.