Extraction and antioxidant property of polyhydroxylated naphthoquinone pigments from spines of purple sea urchin Strongylocentrotus nudus

Purple sea urchin (Strongylocentrotus nudus) spines were dissolved in HCl–ethanol-aqueous solution. The polyhydroxylated 1,4-naphthoquinone (PHNQ) pigments were condensed and purified by using macroporous resin in static adsorption mode. PHNQ in the extract were characterised rapidly by using an ultra-performance liquid chromatography (UPLC) coupled to hybrid quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOFMS). Six known compounds including spinochrome E, 2,7-dihydroxynaphthazarin, spinochrome B, spinochrome C, spinochrome A and echinochrome A, and two new compounds with molecular formula of aminopentahydroxynaphthoquinone and acetylaminotrihydroxynaphthoquinone were identified tentatively. The pigment extract was evaluated for antioxidant activity by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging capacity assay, Fe2+ chelating assay, reducing power assay, lipid peroxidation inhibition assay and tertiary-butyl hydroperoxide (t-BOOH)-induced macrophages protection assay. In all testing methods, the extract showed excellent activity, indicating the PHNQ from S. nudus spines are potential sources of natural antioxidants.