Shiitake (Lentinula edodes) is an edible mushroom native to East Asia and is cultivated and consumed in many Asian countries as well as dried and exported to many countries around the world. It is generally known in the world by its Japanese name, shiitake, derived from the name of the tree upon whose dead logs it is typically cultivated. Extracts from shiitake mushrooms have also been researched for many immunological benefits, ranging from antiviral properties to possible treatments for severe allergies. Shiitake mushrooms are also one of a few known natural sources of vitamin D2.
Shiitake mushroom, the common Japanese name for Lentinula edodes, derives from the mushroom associated with the shii tree (Castanopsis cuspidate Schottky) and take, the Japanese word for mushroom. Because Japan is the world leader in production of this type of mushroom, the mushroom is now widely known by this name. These mushrooms are renowned in Far East countries (e.g., Japan, China, Korea) as a food and medicine for thousands of years.
HABITAT AND DISTRIBUTION
Gregarious on fallen wood of a wide variety of deciduous trees, especially shii, oak, chestnut, beech, maple, sweet gum, poplar (aspen, cottonwood), alder, hornbeam, ironwood, chinquapin, mulberry (Castanopsis cuspidate, Quercus, Castanea, Fagus, Acer, Liquidamber, Populus, Diospyros, Alnus, Carpinus, Morus) in a warm, moist climate. Most of these are raised for artificial cultivation of shiitake mushroom. Shiitake mushroom occurs naturally throughout Southeast Asia.
EDIBILITY AND NUTRITIONAL VALUE
Shiitake are traditionally well-known edible mushrooms of high nutritious value. Raw or dried forms, used in Chinese curative powers of shiitake mushroom, are legendary. Shiitake mushrooms have excellent nutritional value. Their raw fruit bodies include 88–92% water, protein, lipids, carbohydrates as well as vitamins and minerals. It should be noted that amounts of nutrients and biologically active compounds differ in various strains and are affected by substrate, fruiting conditions, and methods of cultivation. Dried shiitake mushrooms are rich in carbohydrates and protein. They contain 58–60% carbohydrates, 20–23% protein (digestibility of 80–87%), 9–10% fiber, 3–4% lipids, and 4–5% ash. The mushroom is a good source of vitamins, especially provitamin D2. It also contains B vitamins, including B1 (thiamine), B2 (riboflavin), B12 (niacin), and pantothenic acid.[1,3,9,10] Minerals found include Fe, Mn, K, Ca, Mg, Cd, Cu, P, and Zn. Water-soluble polysaccharides amount to 1–5% of the dry weight of the shiitake mushroom. The mushrooms’ indigestible polysaccharides, which serve as dietary fiber, include heteroglycan, polyuronide, b-glucan as well as chitin. In shiitake mushrooms, dietary fiber consists of water-soluble materials such as b-glucan and protein and water-insoluble substances extractable only with salts, acids, and alkalies such as polyuronide (acidic polysaccharide), hemicellulose, b-glucan with heterosaccharide chains, lignin, and chitin present as cell wall constituents. The fatty acids account for 3.38% of the total lipids.
Shiitake is one of the best-known and best-characterized mushrooms used in medicine. It is the source of several well-studied preparations with proven pharmacological properties, especially the polysaccharide lentinan, shiitake mushroom mycelium, and culture media extracts
As was stated earlier, lentinan and other polysaccharides from shiitake mushrooms do not attack cancer cells directly, but produce their antitumor effects by activating different immune responses in the host. Lentinan, for example, appears to act as an HDP, which is able to restore or augment the responsiveness of host cells to lymphocytokines, hormones, and other biologically active substances by stimulating maturation, differentiation, or proliferation of cells involved in host defense mechanisms.[19,24] Host defense potentiators are functionally different from biological response modifiers. Thus, lentinan is able to increase host resistance against various kinds of cancer and infectious diseases, including acquired immuno deficiency syndrome (AIDS).[7,28]
The major cause of death in Western countries is coronary artery disease, a primary risk factor for which hypercholesterolemia is a factor contributing to hardening of the arteries. In humans, 50% or more of the total cholesterol is derived from de novo synthesis.[18,35,36] It is known that shiitake mushroom is able to lower blood serum cholesterol (BSC) via a factor known as eritadenine (also called ‘‘lentinacin’’ or ‘‘lentysine’’).
In the last 15–20 yr, shiitake mushroom has been subject to various clinical studies in humans and is thought to be beneficial for a wide variety of disorders including different types of cancer, heart disease, hyperlipidemia (including high blood cholesterol), hypertension, infectious disease, and hepatitis. The mushroom is used medicinally for diseases involving depressed immune function (including AIDS), cancer, environmental allergies, fungal (especially Candida) infection, frequent flu and colds, bronchial inflammation, and regulating urinary incontinence. It was shown that the success of immune adjuvant in therapy depends on the type of cancer (location) being treated, the individual’s general health, immunological and hormonal status as well as the individual’s constitution.