shiitake mushroom
Meaning of shiitake mushroom: A cultivated East Asian mushroom eaten as food and studied in laboratories for a long-chain sugar in its cell walls.
Definition of shiitake mushroom
Shiitake is an edible mushroom, Lentinula edodes, grown on hardwood logs or on sawdust blocks and used widely as food across East Asia and beyond. Its cell walls contain lentinan, a branching chain of glucose units that has been extracted and studied as an immune stimulant. The dried caps also supply B vitamins, copper and dietary fiber.
What is in a shiitake mushroom?
Most of a fresh cap is water. What remains is largely fiber built from long chains of sugar units, together with protein, B vitamins and minerals such as copper and selenium. Drying concentrates the flavor and raises the level of vitamin D when the caps are exposed to sunlight. The savory taste comes mainly from guanylate compounds, which is why dried shiitake is used as a stock ingredient.
What is lentinan?
Lentinan is a beta-glucan, a long chain of glucose units with a particular branching pattern. Immune cells carry receptors that recognize that pattern, because it also appears on the surface of fungi they are built to detect. Binding switches those cells into a more active state. Lentinan has been purified and given by injection in Japan alongside chemotherapy for stomach cancer, and it has been examined in trials in colorectal cancer. It is not approved in that role everywhere, and results outside Japan have been mixed.
Does eating the mushroom do the same thing?
That is the central point of confusion. The studied preparation is a purified extract delivered into the bloodstream, at a concentration nothing like the amount present in a meal. Beta-glucans swallowed whole are large molecules that are poorly absorbed from the gut. Eating shiitake is a reasonable source of fiber and micronutrients, but the evidence gathered on lentinan does not transfer to the food.
Are there recognized harms?
Raw or lightly cooked shiitake can cause shiitake dermatitis, a striking rash of red streaks that looks as though the skin has been whipped. It is attributed to lentinan itself, which is broken down by thorough cooking. The rash settles over a week or two. Handling large quantities of the spores can also provoke a cough and breathlessness in growers.
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Used in a sentence
The dietary history recorded regular consumption of shiitake mushroom in the weeks before the rash appeared.
Good to know
The research on lentinan used a purified extract given by injection, so it does not describe what eating the mushroom does.