Tips on Serving Portobello Mushrooms to Pets Before offering your pet portobello mushrooms, wash them under cold running water and gently cook them. Research suggests the nutritional properties of mushrooms are Boiled taro root with amaranth leaves and mushroom stew. The meal is everything! Did you know that mushrooms are rich in selenium, vitamin D, glutathione and ergothioneine? All these are known to How Functional Mushrooms Can Boost Glutathione Levels Cell line dependent difference in glutathione levels affects the cigarette sidestream smoke induced inhibition of nucleotide excision repair ScienceDirect