Method of producing alginate-derived oligosaccharide through gradient dilution and oxidization

The invention belongs to the field of seaweed chemical researching and development and relates to a method of producing alginate-derived oligosaccharide through gradient dilution and oxidization. The method includes the following steps: adding water to alginic acid, or metal salts thereof, or permannuronic acid fragments and perguluronic acid fragments prepared therefrom to dissolve or disperse the compounds in water; adding an oxidizing agent to the water solution or the sol and heating the water solution or the sol at 80-100 DEG C for 5-20 min; diluting the reaction solution and heating the reaction solution at 50-80 DEG C for 10-60 min; cooling the reaction solution, performing centrifugal separation and evaporating concentration, adding an organic solvent and performing suction-filtration and drying. The reaction system in the invention is a solution or a turbid liquid and the employed oxidant is low in cost, so that the method is high in production speed, is high in yield, is suitable for large-scale production, is strong in polymerization degree consistency of the obtained alginate-derived oligosaccharide and has strong practical application value.