Preparation of phosphorylated chitosan from gladius of the squid Sepioteuthis lessoniana (Lesson, 1830) and its in vitro antioxidant activity

•Chitosan from squid gladius was phosphorylated to prepare water soluble derivative.•The structure was characterized by means of FTIR.•Antioxidant efficacy were determined through various in vitro systems.•Results suggest that phosphorylated chitosan has potent antioxidant abilities.

To evaluate the antioxidant potential of phosphorylated chitosan from the Sepioteuthis lessoniana gladius that is thrown as waste in seafood processing industries. Chitin was extracted from the gladius of S. lessoniana by demineralization and deproteinization. Chitosan was obtained by deacetylation of chitin in strong alkali and phosphorylated by using ortho-phosphoric acid. The structure of phosphorylated chitosan was elucidated through Fourier Transform Infra Red (FT-IR) spectroscopy. The antioxidant efficacy of phosphorylated chitosan was assessed through scavenging activity against 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid diammonium salt) (ABTS), 1, 1-diphenyl-2-picrylhydrazyl (DPPH), superoxide and hydroxyl radicals. The ability to chelate ferrous ion was also assessed. The yield and water solubility of phosphorylated chitosan was calculated as 81% and 78% respectively. The antioxidant activity of phosphorylated chitosan was found concentration dependent. The phosphorylated chitosan scavenges DPPH, ABTS, superoxide and hydroxyl radicals by 56.97%, 76.56%, 71.57% and 56.33% respectively and Inhibitory Concentration (IC50) values of scavenging those radicals were reported as 4.53, 0.46, 0.38 and 0.5 mg/ml, respectively. The chelating ability of phosphorylated chitosan was 59.56% with IC50 of 4.07 mg/ml. Moreover, the antioxidant activity of phosphorylated chitosan was compared with that of the standards such as Butylated Hydroxy Anisole (BHA), ascorbic acid, α-Tocopherol and Ethylene Diamine Tetra Acetic acid (EDTA). The results of the present investigation suggest that the phosphorylated chitosan with potent antioxidant property could be used as an alternative antioxidant that from a natural non-conventional source.