The shiitake stipes were washed with water to remove any impurities, and then were sliced into thin slices and dried by freezing-dry at 50 C. The dried stipeses were powdered using a blender and then were used for extraction. The SSE was obtained using the method of Zhang et al. (2013) with suitable modifications.
Briefly, the powdered stipes (50 g, each extraction batch) was extracted by stirring with 300 mL of distilled water at 100 Con a shaker for 2 h and filtered through Whatman filter paper. The filtrates were dried at 50 C, and the dried SSE was then stored at 4 C to prevent oxidative damage until use.