Antimicrobial, antioxidant and cytotoxic properties of water-soluble polysaccharides extracted from microalgae Isochrysis galbana and Nannochloropsis oculata

The present work is carried out to evaluate potential applications of aqueous extracts of two microalgae Isochrysis galbana (PEA) and Nannochloropsis oculata (PEB) containing mainly polysaccharides. The monosaccharide composition of microalgal extracts was determined. GC–MS analyses after derivatization show that glucose is the major compound in both microalgae PEA (56.88 %) and PEB (68.23 %). Mannitol (38.8 %) and inositol (20.32 %) are respectively the second major compounds in PEA and PEB. Silylation of monosaccharides allows the determination of sorbitol that attained 3.38 % in PEB. The determination of antioxidant, antimicrobial and cytotoxic properties were also analyzed. Antioxidant activity was evaluated from the DPPH scavenging activity. PEA and PEB show a concentration dépendent DPPH·radical scavenging activity. At concentration of 10 mg/mL, both PEA and PEB exhibit an antioxidant activity of 41.45 and 59.07 %, respectively. PEB and PEA are able to inhibit the growth of Gram-negative bacteria, Grampositive bacteria and three Candida species. Cytotoxic activity was evaluated on human HeLa cervical cancer cells. HeLa cell proliferation was totally inhibited after treatment with PEA and PEB (1 mg/mL) and the inhibition was dose dependent (from 0.031 to 1 mg/mL). Their anticholinesterase activity was also investigated against butyrylcholinesterase enzymes. These polysaccharides possess interesting antimicrobial, anticancer and anticholinesterase activities that could represent an additional value for these microalgal products. -- Keywords : algae ; DPPH ; cytotoxic activity ; antimicrobial activity ; polysaccharides ; GC-MS.