Preparation and structural characterization of a partially depolymerized beta-glucan obtained from Poria cocos sclerotium by ultrasonic treatment

A water-insoluble polysaccharide (PCS) obtained by alkaline extraction from the sclerotium of a medicinal mushroom, Poria cocos (PC) was partially depolymerized by ultrasonication for various period of times up to 90 min. The untreated polysaccharide (PCS0) and two mushroom polysaccharides treated for 10 and 90 min (PCS10 and PCS90) were purified by membrane ultrafiltration. PCS90 as a hydrocolloid that had a lower intrinsic viscosity (about 30% of PCS0) and Mw (43 kDa) than PCS0. The 13C NMR spectra of PCS0 and PCS90 indicated that they both had a linear (1 → 3)-β-D-glucan which was further confirmed by methylation analysis. TEM results also showed that ultrasonic treatment could open up the compact structure of PCS into linear chain. PCS90 showed stronger inhibitory effects towards the proliferation of colorectal cancer cell SW620 than PCS0 (IC50 of PCS90 and PCS0 was 32.2 and 169.4 μg/mL, respectively). These results suggested that ultrasonic treatment might be an effective physical method for improving the solution properties of water-insoluble homoglycans such as β-glucan without changing its primary chemical structure and such modified polysaccharides had enhanced their antitumor activity.