Isolation of sodium alginate-like polysaccharide from Padina pavonica: Optimization, characterization and antioxidant properties

In recent years, polysaccharides from brown algae are known to be a topic of various studies, due to their beneficial biological properties including antioxidants activities. In this work, sodium alginate was optimized, extracted, and purified from Tunisian Padina pavonica brown seaweed. Three independent variables were opted: Alkali/algae ratio, extraction temperature, and extraction time. The optimal conditions that were identified are alkali/algae ratio of 50:1 (v/m), extraction temperature of 50 °C, and extraction time of 300 min. An exhaustive physico-chemical characterization was performed via various methods including ATR-FTIR, NMR and thermal analysis (TGA and DSC). The M G^-1 ratio was estimated by deconvolution (M G^-1 = 1.85) indicating that NaalgPP was composed of 65 % mannuronic acid and 35 % guluronic acid. Size exclusion chromatography (SEC) determination revealed that polysaccharide extracted had an average molecular weight of 4890 kDa. The antioxidant potential was assessed through free radical scavenging assays, with the DPPH assay showing the highest activity (76.3 ± 2.3 %), followed by hydroxyl radical scavenging (70 ± 2.3 %) and β-carotene bleaching (62 ± 1.1 %). However, in the ABTS radical-scavenging system, NaalgPP exerted moderate antioxidant capacity (42 % ± 1.3 % inhibition at a concentration of 0.125 mg/ml). These results indicated that sodium alginate-like polysaccharide showed potential as a promising bio-source of antioxidants applied in pharmaceutical or in food industry.