Mushrooms: More Than Just A Tasty Ingredient Did you know that mushrooms are very good for you? Low in calories and filled with nutrients, mushrooms are a great source of B vitamins and minerals. Copper, selenium, potassium, zinc and even manganese are all present in mushrooms. In addition, mushrooms contain a very powerful oxidant. Shiitake, maitake and oysters as well as eryngii (king oyster mushrooms) contain the greatest amounts of the anti-oxidant known as L-ergothioneine. This powerful antioxidant, has been discovered in mushrooms, thanks to a new analytical method capable of identifying this antioxidant in plant material. Mushrooms also contain more protein than most vegetables. Many of these same healthful ingredients are found it dried mushrooms.