Implications of Ultrasonication-assisted Extraction with Response Surface Methodology on Phytochemical Compositions and Antioxidant Activity of Polysaccharide Extract from Phellinus rimosus (Berk.) Pilát Cultivated Mycelia in Northeastern Thailand

Background: Polysaccharides from the medicinal mushroom Phellinus rimosus (Berk.) Pilát (PR) are the major functional bioactive ingredients. However, there has been a marked natural decrease in the number of PR fruit bodies, leading to their increased cost. Moreover, the natural growth and development of mature PR fruit bodies takes several decades. Objective: The objective of this study was to produce a polysaccharide extract from cultured PR mycelia (PEPRM) by using ultrasonic-assisted extraction with response surface methodology (RSM), and determine its physicochemical composition and antioxidant potential. Methods: Polysaccharide and monosaccharide composition analyses were carried out by Fouriertransform infrared spectroscopy (FT-IR) and High-performance liquid chromatography (HPLC). Total contents of polysaccharides, beta-glucans, phenolic compounds, and flavonoids were investigated utilizing the phenol-sulfuric acid method, enzymatic-based commercial test kit, Folin-Ciocalteu method, and aluminium chloride colorimetric method, respectively. Antioxidant activity was determined by using 2,2-diphenyl-1-picrylhydrazyl-hydrate (DPPH) radical scavenging assay and 2,2- azino-bis (3-ethylbenzothiazol-6-sulfonic acid) (ABTS) radical cation decolorization assay. Results: Optimal conditions for the production of PEPRM included a ratio of 51.29 mL water to 1 g PR mycelia and an extraction time of 46.23 minutes, resulting in a total polysaccharide content of 577.5 mg/g of PEPRM. FT-IR spectra of PEPRM showed two broad bands at 3272.08 cm^-1 and 2924.8 cm^-1 in the carbohydrate region and the peaks at 1078.44, 1019.05, and 853.0 cm^-1 indicated the presence of the pyranose ring skeleton, glycosidic linkage, and glucans. PEPRM had molar ratios of glucose: mannose: rhamnose: Fucose, i.e., 21.86: 1.00: 2.08: 3.40, respectively. PEPRM had total contents of beta-glucans, phenolic compounds, and flavonoids as percentages of dry weight, i.e., 21.22, 2.51, and 5.71, respectively. PEPRM showed better inhibitory activity against ABTS radicals than DPPH radicals. Conclusion: This is the first finding to reveal that ultrasonic-assisted extraction with RSM was an environmentally friendly alternative to produce antioxidant polysaccharides from cultured PR mycelia.