Antioxidant activities and characterisation of polysaccharides isolated from the seeds of Lupinus angustifolius

Lupinus angustifolius (blue lupin) is produced abundantly in Australia and used mainly as animal feed. However, these seeds have excellent nutritional value with high protein, high dietary fibre and low fat content with a huge potential for value addition. In the present study, blue lupin polysaccharides have been isolated and their biological activities investigated. Hot water extraction and size-exclusion chromatography yielded six polysaccharide fractions that have been designated as BLP-1, BLP-2, BLP-3, BLP-4, BLP-5 and BLP-6. Gas chromatography was employed to determine the mono-sugar compositions of these fractions which showed the existence of galactose, fucose, rhamnose, glucose, mannose, ribose and xylose. The antioxidant activities of all the fractions were investigated using ABTS+* radical scavenging activity and ferrous chelating activity. Immunostimulatory activities of these fractions were measured by treating the mouse macrophages (RAW 264.7) and monitoring the production of nitric oxide (NO) by Griess reagent method. Three of the blue lupin polysaccharides (BLP-1, BLP-2 and BLP-5) displayed significant antioxidant activities. Some of the fractions have effectively stimulated mouse macrophages in a concentration-dependent manner indicating their immunostimulatory capability. FT-IR spectroscopic technique was employed for a preliminary structural characterisation of the active polysaccharide fractions.