Method for preparing low molecular weight brown seaweed fucoidan sulfate

The invention relates to a method for preparing low molecular weight brown seaweed fucoidan sulfate. The method comprises a step of oxidatively degrading brown seaweed sulfated polysaccharides by hydroxyl radical and a step of ultrafiltration membrane separation and purification, wherein raw sugar of the brown seaweed sulfated polysaccharide is used as a raw material, the hydroxyl radical generated by the reaction of copper ions and hydrogen peroxide is adopted to oxidatively degrade the raw sugar of the brown seaweed sulfated polysaccharide, and the membrane separation technology is combined in the method for preparing the low molecular weight fucoidan sulfate from the brown seaweeds. In the preparation process, the oxidizing speed is uniform, the reacting condition is mild, and the controllability and repeatability are good; the copper ions are removed by a chelating column after the oxidation reaction is finished, so the operation process is simple. Furthermore, the pH value is adjusted by adding little acid and alkali, so the salt content in the product is low, and can be completely removed by a 300Da ultrafiltration membrane in the ultrafiltration membrane separation and purification process. The ultrafiltration membrane can effectively separate and purify the brown seaweed fucoidan with different molecular weights along with high separating speed and large treatment amount. The method is suitable for industrial production.