Structural characterization, antioxidant and antibacterial activities of two heteropolysaccharides purified from the bulbs of Lilium davidii var. unicolor Cotton

Abstract Two heteropolysaccharides, BHP-1 and BHP-2, were separated and purified from the edible bulbs of Lilium davidii var. unicolor Cotton by anion-exchange and gel-permeation chromatography. The primary structural characteristics of BHP-1 and BHP-2 were investigated by Congo red test, X-ray diffractometry (XRD) analysis, IR, GC and NMR. The results showed that the weight-average molecular weight (M W ) and number-average molecular weight (Mn) of BHP-1 and BHP-2 were nearly 1.93 × 10 5  g/moL, 8.86 × 10 4  g/moL and 3.52 × 10 4  g/moL, 2.95 × 10 4  g/moL, respectively. Glucose and mannose comprised BHP-1 in a relative molar ratio of 5.9:2.0, and BHP-2 was consisted of glucose, galactose, mannose and arabinose with approximate molar ratios of 8.3:1.5:1.0:1.1. Their backbone mainly contained α-(1 → 4)-linked d -glucopyranosyl. In addition, the C-6 of the glucose and C-2 of mannose residue of BHP-1 and BHP-2 were substituted. The two polysaccharides were semi-crystalline substance with multi-branching structure and triple helix conformation. Bioassays showed that BHP-1 and BHP-2 had effective antioxidant activities evaluated by DPPH, scavenging superoxide radical and OH radical in a dose-dependent manner. The two heteropolysaccharides also displayed distinct and selective antibacterial activity against B. cereus , P. putida , M. luteus and K. pneumonia with inhibition zones of 13 mm, 16 mm, 17 mm, 23 mm and 12 mm, 17 mm, 19 mm, 20 mm, respectively. These findings provided a reference for potential applications of the polysaccharides from L. davidii as natural antioxidants and antibacterial agents in food and pharmaceuticals.