Isolation, purification, and metal-induced gelation of released polysaccharides from spent culture medium of Arthrospira

Cyanobacteria release polysaccharides that accumulate in the culture medium. In this study, released polysaccharides were isolated from the spent culture medium of an Arthrospira farm with a carbohydrate concentration of 136 mg L-1. The polysaccharides were concentrated 5.2 times by ultrafiltration using a 50 kDa polysulphone membrane and purified (desalting, protein removal). The polysaccharides were rich in uronic acid (159 mg g-1), had a low sulfate content (2.3 mg g-1), and contained 9 different monosaccharides, with 2-deoxyD-galactose (27.9 %), fucose (22.7 %), glucose (22.0 %), and glucuronic acid (17.1 %) being dominant. A 1 % w/ v polysaccharide concentrate formed stable gel beads in Al3+ and Fe3+ solutions. Rheological characterization of the gel revealed stable storage (G' = 38 Pa) and loss modulus (G" = 6 Pa) over a wide frequency range. This study demonstrates the feasibility to recover polysaccharides from Arthrospira spent culture medium and the potential to use these polysaccharides in food or biotechnological applications.