Effects of drying on the structural characteristics and antioxidant activities of polysaccharides from Stropharia rugosoannulata

Abstract

We investigated the structural characteristics and antioxidant activities of two types of neutral polysaccharides and two types of acidic polysaccharides from Stropharia rugosoannulata under different drying methods. Fresh S. rugosoannulata were processed with freeze-vacuum drying (FVD) and hot-air drying (HAD). Polysaccharides from the dried S. rugosoannulata (SRP) were purified using a DEAE-52 cellulose column to obtain two types of neutral SRPs (FSRP-1 and HSRP-1) and two types of acidic SRPs (FSRP-2 and HSRP-2). We found that drying can affect the structural characteristics and antioxidant activities of SRPs. Varied monosaccharide compositions were found in FSRP-1, FSRP-2, HSRP-1 and HSRP-2, and HAD-treated SRP had more glucose and less galactose. The (1 → 6)-α-D-Galp linkage was the primary chain in FSRP-1 and HSRP-1, whereas the (1 → 3)-β-D-Glcp was the backbone structure in FSRP-2 and HSRP-2. Our results thus suggest that hot air drying changed the β-configuration in polysaccharides. FSRP-1, FSRP-2, HSRP-1 and HSRP-2 had positive ferric ion reducing antioxidant power and scavenging activities on ABTS⁺ and hydroxyl radicals, whereas HSRP exhibited a stronger antioxidant activity than that of FSRP. Hot-air dried S. rugosoannulata could therefore be recommended as a suitable candidate for use in the preparation of antioxidant polysaccharides as functional foods.

Keywords: Antioxidant activity; Characterization; Drying; Polysaccharides; Stropharia rugosoannulata.

Fig. 1

Elution profile of SRP on DEAE-52 chromatography column with gradient of NaCl solution (0 and 0.3 M)

Fig. 2

HPLC chromatogram of standard monosaccharides (a) and hydrolyzed FSRP-1 (b), FSRP-2 (c), HSRP-1 (c) and HSRP-2 (e). Peak identities: Mannose (1), Ribose (2), Rhamnose (3), Glucuronic acid (4), Galacturonic acid (5), Glucose (6), Galactose (7), Xylose (8), Arabinose (9), and Fucose (10)

Fig. 3

FT-IR spectrum of FSRP-1, FSRP-2, HSRP-1, and HSRP-2

Fig. 4

¹H NMR (a) and ¹³C NMR (b) spectra of FSRP-1, FSRP-2, HSRP-1, and HSRP-2

Fig. 5

Antioxidant activity of FSRP-1, FSRP-2, HSRP-1, and HSRP-2. (a) ABTS⁺ radical scavenging capacity; (b) Hydroxyl radical scavenging capacity; (c) FRAP abilities, different letters (a, b, c and d) indicate significant differences (P < 0.05)