About Shiitake Mushroom
What is Shiitake?
Shiitake (Lentinula edodes) are the mushrooms that the Chinese affectionately named “Xiang-gu” (or “Shiang-gu”), “the fragrant mushrooms”. They are a treasured and traditional delicacy at dinner tables in China, Japan, and Korea. These favorite mushrooms from the Orient are not only delicious and nutritious food with great flavor and an enticing aroma, but they also contain a material well-known for its medicinal benefits. Lentinan (-1, 3 glucan with -1, 6 and -1, 3 glucopyranoside branchings), a water-soluble polysaccharide produced and extracted from shiitake, is an approved anticancer drug in Japan. Native to the Far East, shiitake have been found in the wild only in such places as China, Japan and Korea until recently. Two recent findings of shiitake in natural habitats in the United States could have originated from disposed fibrous stems of fresh shiitake. Mushrooms that grow primarily in temperate climates, shiitake grow singly or in clusters in declining or dead hardwoods, in particular, Shii (Pasania spp.), oaks (Quercus spp.), and other Asian oaks and beeches (Stamets, 2000). In nature, shiitake are saprophytic white-rot fungi that degrade woody substrates containing recalcitrant, hard to decompose, lignin components. It is due to this capacity that wood logs and sawdust are now used as substrates to cultivate shiitake. Fleshy gilled mushrooms, shiitake produce white spores and white mycelia. How the four basidiospores in shiitake are formed on a basidium was described vividly through electron-scanning microscopy by Wu (2000). Shiitake usually have central stalks attached to circular-shaped mushroom caps that are light tan to dark brown and 5-25cm across. Some strains produce light-colored mushrooms, while others produce dark ones. Some shiitake have a nice flecking with velvety white hairy material on the caps. Growers are aware what kind of shiitake consumers want in their targeted markets.
Benefits of Shiitake
Shiitake has long been favored by Asian people as a gourmet and medicinal mushroom. They eat shiitake stir-fried, in soup and in decoction. Today shiitake is found in markets throughout North America and Europe as well as Asia. It is the world’s 2nd most commonly cultivated mushroom. Shiitake’s popularity is ever increasing throughout Asia, North America, Europe and other parts of the world, partly because of its exotic flavor and partly because of its nutritional and various medicinal properties. This delicate mushroom is also excellent in its nutritional value. It is a particularly good source of minerals and vitamins B1 (thiamin), B2 (riboflavin), B3 (niacin) and D. It also contains all the essential amino acids and dietary fiber1. The caloric value of 100g of dried shiitake is higher than 100g of raw potatoes (80 kcal) or beef loin (224 kcal), but lower than that of whole wheat or brown rice (328-350 kcal). The protein content of dried shiitake is comparable to that of chicken, pork and beef but the fat count is much lower and the dietary fiber count is considerably higher than those meats. Shiitake contains almost all the essential amino acids, with lysine and arginine being particularly abundant (Liu and Bau, 1980), and methionine and phenylalanine less abundant (Lasota and Sylwestrzak, 1989). In laboratory analysis it was found that amino acids, protein, glycogen, lipids, ascorbic acid, and total ash contents increased as the fruiting body developed (Fasidi and Kadiri, 1990). Based on these findings, it may be desirable to consume fully mature fruiting bodies for maximum nutritional value. The researchers generally found higher concentrations of nutrients in the cap than the stem of the fungus. Shiitake contains dietary fiber in the ratio of 6.7 g per 100g of dried shiitake, which is a figure much higher than that for brown rice (0.2g), and sweet potatoes (0.9 g). Dietary fiber prevents constipation, obesity, diabetes, hypertension, colon cancer and arteriosclerosis by lowering cholesterol level. In addition to dietary fiber, dried shiitake contains higher contents of potassium (K), iron (Fe), phosphorus (P) and vitamin B and D than most food sources. But it does not contain vitamins A and C. The high amount of ergosterol in fresh shiitake makes dried shiitake an important vitamin D source because ergosterol converts to vitamin D2 in the presence of sunlight. Studies have shown that exposing shiitake to direct sunlight for 3 hours/day increases the vitamin D2 content up to 5 times. Sunlight exposure also increases the free amino acid content which is about 2,180mg/dl in the dry fruiting bodies, and it makes them sweeter and less bitter (Kiribuchi, 1991). Eating shiitake can prevent various vitamin B and D deficiencies including beri-beri2 (thiamin); cheilosis3, glossitis4, corneal vascularization5, Seborrheic dermatitis6, nerve tissue damage (riboflavin); abnormal growth in infants and children (niacin); and rickets7 (vitamin D). Vitamin D boosts calcium absorption and thus plays an important role in bone formation.
Taxonomy
In different parts of the world, shiitake is known by different names. The name shiitake (shii-mushroom) is derived from Japanese words: “shii” meaning the hardwood of Pasania spp. and “take” meaning mushroom. The name shiitake is now the most popular name for this mushroom that is the most popular specialty mushroom worldwide. In the U.S. it is also known as the black forest mushroom. In France, it is known as lectin. In China, different forms of shiitake are known by various names such as xiang-gu, the fragrant mushroom, dong-gu, the winter mushroom, and hua-gu, the flower mushroom or variegated mushroom (Chen, 2001). This abundance of different local common names for the same species illustrates the importance of having a universal name that everyone understands. The scientific name for shiitake is Lentinula edodes (Berkeley) Pegler. Based on macro- and micro- morphological characteristics as well as other features including DNA analysis, L. edodes is classified in the genus of Lentinula, the family of Tricholomataceae, the order of Agaricales, and the subphylum of Basidioimycotina. For a long time shiitake was known as Lentinus edodes (Berk.) Singer, especially among mushroom growers. In 1975, Pegler proposed this species be transferred to Lentinula. The rationale of the transfer was based on microscopic studies. The genus Lentinula is monomitic (one kind of mycelium), so the species in this genus do not contain dimitic (two kinds of) hyphae in the mushroom flesh seen in the genus of Lentinus. The cells are arranged in the mushroom gill trama in a parallel and descending fashion instead of having highly irregular or interwoven cells in the gill trama as in the genus of Lentinus. Recent DNA studies also support placement in the Lentinula genus. Mushroom growers, however, continued to use the old name Lentinus edodes until the 1980’s and beyond. The name Letinus edodes was still used in 1989 and 1992 in two important books. It is helpful to keep in mind this historical name, Lentinus edodes (Berk.) Singer, when conducting literature searches or other explorations. Shiitake Mushroom is looks like a deer’s skin so In Nepal Shiitake is called Mirge as in Nepali Language deer is called Mirga.
Shiitake in Medicine
Shiitake is used medicinally for diseases involving depressed immune function, including cancer, AIDS, environmental allergies, and frequent flu and colds. It also appears beneficial for soothing bronchial inflammation and regulating urine incontinence (Liu and Bau, 1980), as well as for reducing chronic high cholesterol. According to one prominent Japanese researcher, lentinan is an immunomodulating agent. For older persons, it serves as a general rejuvenating agent, no matter what the condition of their health. For young people, it presents a potent protection from overwork and exhaustion (Aoki, 1984b) or chronic fatigue syndrom. In Japan, lentinan is currently classified as a drug, whereas LEM is considered a food supplement. As more clinical research on shiitake and preparations isolated from shiitake is published, the effective range of application will be more broadened. But the highly purified compounds including lentinan and LEM are subject to a particular situation or individual. Addition of shiitake to a daily diet is highly recommended to maintain good nutrition, to boost the immune system and to prevent various diseases. Shiitake containing almost all essential amino acids will serve as an excellent protein supplement.
References: 1.Mushroom Growers’ Hand Book 2.Center for Agricultural Technology and Training (CATT)