A study conducted by Spanish researchers have concluded that mushrooms are best preserved when it's microwaved or grilled to preserve more its nutritional values. They also said that it would be better than the usual method of boiling and deep frying.

In the study published in International Journal of Food Sciences and Nutrition titled "Effect of different cooking methods on nutritional value and antioxidant activity of cultivated mushrooms," the researchers revealed that mushrooms cooked by microwave or grill are not losing its nutritional values compared to boiling or frying. Based on their observation, the content of polyphenol and antioxidant activity has significantly increased once microwaved or grilled.

"When mushrooms were cooked by microwave or grill, the content of polyphenol and antioxidant activity increased significantly," lead author Irene Roncero said. She also said that there are no significant losses in the nutritional value of the cooked mushrooms with that method of cooking.

The mushrooms used in this study are white button mushroom, shiitake, oyster mushroom, and king oyster mushroom. If one wants to add some portion of oil during the grilling of mushrooms, it is not a problem for maintaining the nutritional value according to Roncero. She added that the antioxidant capacity can be even improved as the use of olive oil could actually increase the calorie content of the food. 

Roncero also underlined the cooking technique and its influence on the nutritional value and antioxidant activity of mushrooms. "The adequate selection of the culinary method is a key factor [in] preserving the nutritional profile of this highly consumed food," she said.

In an article published in Science Daily, the study also found out that frying cause severe losses of protein, ash and carbohydrates content in the mushrooms. Boiling, on the other hand, decreased the antioxidant activity.

"Frying and boiling treatments produced more severe losses in proteins and antioxidants compounds probably due to the leaching of soluble substances in the water or in the oil," Roncero said. Furthermore, she said that frying mushrooms only increased the fat and energy while boiling only increased the total glucans content.