Effect of different drying methods on physicochemical properties and antioxidant activities of polysaccharides extracted from mushroom Inonotus obliquus

Inonotus obliquus is a kind of mushroom which has long been used as a folk remedy for curing various diseases such as cancers, heart disease and diabetes in Russian and Eastern Europe. Polysaccharides are one of the main bioactive constituents of Inonotus obliquus with health functions. Three drying methods, freeze drying, hot air drying and vacuum drying methods were comparatively studied on the physicochemical and antioxidant properties of Inonotus obliquus polysaccharide (IOPS) with chemical methods: gas chromatography, size exclusion chromatography, scanning electron micrograph, 1,1′-diphenyl-2-picrylhydrazyl (DPPH) assay, ferric reducing power assay and lipid peroxidation inhibition assay, respectively. Results showed that physicochemical and antioxidant properties of IOPS differed from each other after the treatment of the three drying methods. Compared with hot air drying and vacuum drying methods, freeze drying method resulted in the properties of IOPS with lower molecular weight distribution, a hyperbranched conformation with triple helix, higher antioxidant abilities on DPPH radical scavenging, ferric-reducing power and lipid peroxidation inhibition activity. Freeze drying was a good choice for the preparation of polysaccharides from Inonotus obliquus and could be used to produce antioxidants for food industry. ► Inonotus obliquus is a kind of mushroom with multiple heath effects. ► Polysaccharide is one of the main bioactive constituents of Inonotus obliquus. ► Three drying methods were comparatively studied on the properties of polysaccharide. ► Higher antioxidant abilities was found in freeze dried polysaccharides. ► Freeze drying method was a good choice for the preparation of polysaccharides.