Extraction optimization, structure and antioxidant activities of Fortunella margarita Swingle polysaccharides

The objective of this study was to maximize the yield of polysaccharides extracted from Fortunella margarita Swingle (FMPS) and investigate the relationship between the structure and antioxidant activities. The optimal conditions for ultrasonic-assisted extraction (UAE) of FMPS were ultrasonic power 171 W, extraction temperature 50 °C, water volume to raw material weight (W/M) ratio 32 ml/g and extraction time 87 min. Under these conditions, the yield of FMPS was 4.15 ± 0.11% (w/w), which was increased by 129.28% compared to hot water extraction. FMPS3, the main fraction of FMPS, was isolated by DEAE Sepharose CL-6B column chromatography. According to size-exclusion chromatography, multi-angle laser light-scattering and refractive index (SEC-MALLS-RI), the molecular weight (Mw), polydispersity index (Mw/Mn) and root-mean-square turning radius (Rg) of FMPS3 were 4.58 × 105 (±2.02%) Da, 1.08 (±1.23%), 28.13 (±1.73%) nm, respectively. FMPS3, linked mainly by β-glycosidic bonds, consisted of galactose, galacturonic acid, glucose, mannose and rhamnose as shown by HPLC, FT-IR, 1H NMR and 13C NMR. Furthermore, FMPS3 displayed strong scavenging ability against hydroxyl, superoxide and DPPH radicals. The activity was affected by the monosaccharide composition, molecular weight and proportion of β-glycosidic bonds and was a result of a combination of multiple structural factors. FMPS3 is potentially a novel natural antioxidant agent.