L-ergothioneine is a powerful antioxidant phytonutrient found in highest concentration in mushrooms.
Studies show that shiitake, oyster, king oyster and maitake mushrooms contain the highest amounts of ergothioneine, with up to 13 mg in a 3-ounce serving. Portabellas and criminis come in next, followed by white buttons which contain up to 5 mg per three ounce serving (which is 12 times as much as wheat germ and 4 times more than chicken liver).
L-ergothioneine is not destroyed when mushrooms are cooked, so saute, bake and steam away! You'll still enjoy the healthy benefits.
Dubost N, Beelman R, Peterson D, Royse D. Identification and quantification of ergothioneine in cultivated mushrooms by Liquid Chromatography – Mass Spectroscopy. The 230th ACS National Meeting, Washington, D.C., Wednesday, August 31, 2005.