UV/H2O2-Mediated Fucoidan Degradation

Fucoidan was obtained from Qingdao Mingyue Seaweed Group Co., Ltd. It was extracted from Undaria pinnatifida. The dry Undaria pinnatifida powder was extracted in hot water at 100 °C for 4 h with a solid–liquid ratio of 1:50 (w/v). The residue was removed using filtration and centrifugation and the extraction solution was concentrated using a vacuum rotary evaporator (Hei-VAP values Digital, Heidoph, Nuremberg, Germany). The polysaccharide was precipitated using ethanol. The mixtures were kept at 4 °C for 12 h and then the polysaccharide precipitate was obtained using centrifugation at 8000 rpm for 20 min and dried at room temperature. The fucoidan obtained after the precipitated solution was freeze-dried (vacuum freeze dryer, ALPHA 1–2 LDplus, Christ, Osterode, Germany).
The fucoidan was degraded by UV/H₂O₂. Firstly, 25 mL 2.4 mg/mL Fuc solution, 3 mL H₂O₂, and 2 mL deionized water were transferred into a 90 mm culture dish. The final concentration of H₂O₂ was 100 mmol/L, the irradiation dose was 6500 mJ/cm² and the final concentration of the Fuc was 2 mg/mL. Mixtures were treated in a UV irradiation system (HOPE-MED 8140, Hepu, Beijing, China) for 0, 15, 30, 45, 60, 75, 90, 120, 150, and 180 min, respectively. In the end, catalase was used to remove residual H₂O₂ from each group. Finally, the degraded fucoidan obtained after the solution was concentrated using a vacuum rotary evaporator (55 °C, 100 rpm) and then freeze-dried.