Identification and characterization of antioxidant and immune-stimulatory polysaccharides in flaxseed hull

•Flaxseed hull polysaccharides were isolated, fractionated, and identified.•The polysaccharide fractions possessed high antioxidant capacity.•The fractions had good immune-enhancing activities partly via the MAPK pathway.•These polysaccharide fractions may be useful as functional food ingredients. Flaxseeds are widely consumed for their desirable sensory attributes and health benefits. We focused on enhancing the sustainability and economic potential of flaxseeds by characterizing functional attributes of polysaccharides isolated from flaxseed hull residues. In particular, antioxidant and immune-stimulatory polysaccharides were isolated and purified from flaxseed hull. Infrared spectroscopy was used to identify the key functional groups. The polysaccharides were composed of mannose, rhamnose, galactose, glucose, galactose, xylose, arabinose, and fucose. In vitro studies showed certain flaxseed hull polysaccharide fractions exhibited strong antioxidant activities, increased nitric oxide levels, and enhanced the production of cytokines (TNF-α and IL-6). In the presence of 200 μg/mL of one of these fractions, the levels of p-ERK, p-JNK, and p-p38 increased significantly by 1.8-, 9.0-, and 6.7-fold. These polysaccharide fractions may exhibit their immune-regulatory properties partly by modulating the MAPK pathway. The flaxseed hull polysaccharides identified have potential application as natural antioxidants and immune-enhancing nutraceuticals.