November 2010 Issue

From A to Shiitake — Japanese Mushrooms May Offer Certain Benefits
By Leslie K. Kay, MS, RD
Today’s Dietitian
Vol. 12 No. 11 P. 20

Fall is a great season to enjoy an exotic food once reserved for royalty. While often considered a vegetable and prepared like one, the mushroom is actually a fungus, a special type of living organism with no roots, leaves, flowers, or seeds. A time-honored food in many cultures, mushrooms have traditionally been used as an antitumor, antifungal, and antiarthritic medicinal food. Today, mushrooms have emerged as quite the powerhouse in terms of both flavor and nutritional value. A notable source of B vitamins, phosphorus, magnesium, potassium, and selenium, mushrooms are also a significant source of fiber, with 3 g in a typical 3.5-oz serving.

Mushrooms are the only “plants” that provide a natural source of vitamin D. Similar to the way humans absorb sunlight and convert it to vitamin D, mushrooms contain a plant sterol—ergosterol—that converts to vitamin D2 when exposed to ultraviolet light. Due to natural variability, vitamin D levels can range from 1% to 97% of the Daily Value (400 IU) per raw 84-g serving.

Japanese Varieties
Ounce per ounce, mushroom species pack a phytochemical punch, containing compounds that may reduce cancer risk and improve immune function. Although many mushroom varieties exist, this article focuses on the Japanese mushrooms with the most potential medicinal benefits and flavor to boot.

King Trumpet
King trumpet (Pleurotus eryngii), also known as king oyster, is an edible mushroom native to regions of Europe, the Middle East, and North Africa but also commercially grown in Japan and the United States. The largest species of the oyster mushroom, it has a thick white stem and a small tan cap and is known for its robust, somewhat earthy flavor and more meaty texture.

King trumpet contains high amounts of ergothioneine, a naturally occurring antioxidant amino acid. L-ergothioneine has a very high Oxygen Radical Absorbance Capacity value and is concentrated in organs exposed to high oxidative stress (eg, kidneys, liver, eyes).1 Antioxidants such as L-ergothioneine may help reduce the risk of chronic disease by providing cellular protection against free radical damage. Investigations with supplemental L-ergothioneine in rats demonstrated protection against induced lipid peroxidation of the liver and kidneys and also conserved the consumption of endogenous glutathione and alpha-tocopherol.2

While all mushrooms contain some ergothioneine, specialty mushrooms such as king trumpet and maitake contain higher amounts than shiitake or white button varieties; a standard 3-oz serving can contain up to 13 mg. As with most phytochemicals, ergothioneine levels do not decrease during cooking.

King trumpet also contains statins such as lovastatin, which has been shown to significantly reduce cholesterol levels in rats.3 In a small clinical study, 30 subjects with diabetes ingested oyster mushrooms over a 21-day rotation period.4 Subjects demonstrated significant reductions in total cholesterol, triglyceride, and glucose levels. Beta-glucans found in many mushrooms may also have a lipid-lowering effect.

In the produce aisle, mushrooms are the leading source of the essential antioxidant selenium. The king trumpet mushroom has the ability to extract and concentrate high levels of selenium from its environment.5 The selenium in mushroom tissue is organically bound and much easier to absorb than inorganic selenium in most dietary supplements.

The maitake mushroom (Grifola frondosa) grows in clusters at the base of trees (particularly oaks) and is native to the northeastern part of Japan and North America. Valued in traditional Chinese and Japanese botanical medicine as an aid to balance organ function, the mushroom is commonly known as “hen of the woods” in English; in the Asian market, its Japanese name maitake means “dancing mushroom.”

Maitake is especially high in antioxidants such as ascorbic acid, tocopherols, phenolic compounds, carotenoids, and L-ergothioneine. It contains complex polysaccharides, which act as immunomodulators and possess antitumor activity. In 2009, a phase 1/2 clinical trial conducted by Memorial Sloan-Kettering Cancer Center showed that maitake could stimulate the immune systems of patients with breast cancer. The beta-D-glucan polysaccharides present in maitake have been studied as a potential aid for preventing and treating cancer and as an adjunctive treatment for HIV infection.6 Preliminary research suggests that maitake mushroom extracts can prevent the metastasis of experimentally induced tumors as well as prevent tumor occurrence in normal cells.7

Additionally, preliminary clinical evidence suggests that maitake mushroom polysaccharides may lower blood glucose in people with type 2 diabetes, possibly by activating insulin receptors.8 Research in rats suggests that maitake mushroom can lower blood pressure and improve lipid profiles in experimental hyperlipidemia.9,10

The shiitake mushroom, native to Japan and other Asian nations, is cultivated worldwide for its purported health benefits. The fresh and dried forms are commonly used in East Asian cooking. Shiitake contain lentinan (1,3 Beta-D-glucan), thought to have anticancer effects in colon cancer cells, which may be due to its ability to suppress cytochrome P450 1A enzymes that are known to metabolize procarcinogens to active forms.

Studies conducted with shiitake extracts in vitro and in mice revealed the mushroom’s antiproliferative, immunostimulatory, hepatoprotective, antimutagenic, and anticaries properties, but a clinical trial failed to show effectiveness in the treatment of prostate cancer.11

White and Brown Beech
Relative newcomers to the market are the Japanese white beech (Bunapi) and brown beech (Bunashimeji) mushrooms, originating in Japan and now grown and cultivated in the United States. These delicate fungi have a nutty, buttery flavor and a firm, crunchy texture. The mushrooms grow in clusters. White and brown beech mushrooms also contain beta-glucan polysaccharides, known for their immune-modulating and antitumor properties.12

Native to North America, China, and Japan, the reishi mushroom (Ganoderma lucidum) has a purple-brown color with a long stalk and distinctive shiny cap shaped like a fan. Prized for its purported health benefits rather than its strong flavor, it grows on plum and oak trees. The reishi mushroom has traditionally been used for enhancing the immune system and addressing hypertension, hyperlipidemia, cardiovascular disease, and asthma and bronchial diseases.

Reishi occurs in six different colors, but the red variety is most commonly used and commercially cultivated in East Asia and North America. In vivo and in vitro studies have identified the active components of reishi mushrooms are primarily polysaccharides, including beta-glucans and triterpenes, and seem to have a variety of pharmacological effects, including antioxidant, antitumor, immune-modulating, cardiovascular, antiviral, and antibacterial effects.13,14

Savor the Flavor
All mushrooms are a rich source of umami, the fifth basic taste after sweet, salty, bitter, and sour. Derived from the Japanese word umai, meaning “delicious,” umami is usually described as a savory, brothy, rich, or meaty taste sensation. Umami contributes a satisfying flavor and full-bodied taste with distinctive aroma and mouthfeel. The more umami present in food, the more flavorful it will be. All mushrooms contain umami; the darker the mushroom, the more umami it contains. Cooking at high heat, such as sautéing or grilling, or for longer periods (eg, cooking soup or broth) will intensify and develop the mushroom flavor.

Preparation Tips
Grilling or broiling is a preferred method for preparing the larger mushrooms such as the maitake and king trumpet, as high heat develops their characteristic flavor. Lightly brush caps and stems with oil to keep them moist and then season them with salt and pepper. Grill or broil 4 to 6 inches from the heat source for 4 to 6 minutes on each side, brushing again once or twice. Mushrooms may also be roasted or sautéed with oil, butter, or vegetable broth to help develop flavors. Because mushrooms are so high in moisture, they also microwave well without the addition of butter or margarine. For a lower-fat option, sauté with a few tablespoons of wine or broth (instead of oil or butter) until the released juices have evaporated, about 5 minutes.

Final Thoughts
Neither vegetables nor fruits, mushrooms may contribute significantly to a plant-based diet high in nutrients, including phytochemicals. And while exotic mushrooms may be new to some, all contribute flavor, texture, and possible health benefits.

— Leslie K. Kay, MS, RD, is a clinical dietitian who provides technical support for the food and dietary supplement industry.


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