Isolation, In Vitro Antioxidant Capacity, Hypoglycemic Activity and Immunoactivity Evaluation of Polysaccharides from Coriandrum sativum L.

Coriander (Coriandrum sativum) is a classical medicinal and edible herb as well as a spice, but the physicochemical and biological properties of its polysaccharides have not been fully studied. In this study, the polysaccharides were extracted using an ultrasonic-assisted method and purified from fresh coriander, and then the coriander polysaccharide (CSP) fraction was separated using an agarose gel Q-Sepharose Fast Flow column. The total sugar content, protein content and monosaccharides composition of CSPs were determined using a phenol-sulfuric acid method, Coomassie Brilliant Blue method and HPLC. The structural characterization was detected using ultraviolet spectrophotometry and FT-IR spectroscopy. DPPH and ABTS free radicals were used to explore their antioxidant activities, while the inhibitory abilities of α-amylase and α-glucosidase were used to evaluate their hypoglycemic activity. After that, the immunomodulatory and antitumor activities were investigated using macrophage RAW264.7 and HepG2 cells as the targets. The results showed that the total sugar and protein contents of CSPs were 66.90 ± 1.44% and 1.06 ± 0.32%, respectively. CSPs were mainly composed of fucose, rhamnose, arabinose, galactose, glucose, galacturonic acid and glucuronic acid, with a molar ratio of 1.13:15.11:9.60:25.98:1.55:44.33:2.29, and may be an acidic heteropolysaccharide containing pyran rings, α- and β-glycosidic bonds and glucuronic acid. Results from in vitro experiments of biological activities showed that the IC₅₀ of CSPs for scavenging DPPH and ABTS free radicals were 0.759 mg/mL and 1.758 mg/mL, respectively; the IC₅₀ values for inhibiting the activities of α-amylase and α-glucosidase were 0.634 mg/mL and 2.178 mg/mL, respectively; the CSPs with a concentration of 25~200 μg/mL showed no obvious toxicity to macrophage RAW264.7, and when treated with 100 μg/mL of CSPs, the relative cell phagocytosis capacity and secreted nitric oxide amount of RAW264.7 were 153.75 ± 12.01% and 133.56 ± 5.37%, respectively; CSPs showed a concentration-dependent ability to inhibit the growth of HepG2 cells within the test concentration of 0.25-2.0 mg/mL. Summarizing the results, due to their excellent antioxidant, immunomodulatory and anti-tumor activities, the coriander acid polysaccharides were expected to show good potential in comprehensive development of food and medicine.