Preparation method of alginate oligosaccharides

A preparation method for alginate oligosaccharides includes following steps: adding the water to the alginic acid or metal salt or the produced high mannuronic acid, high guluronic acid section to dissolve or disperse in the water, adding it to the oxidant solvent in a radiation condition, heating the solution to 60-80 DEG C for 4-50 minutes, then cooling the solution, concentrating the solution by nanofiltration film, drying the concentrated liquid by spray. The invention improves the product quality by preventing the product over-oxidation by the radiation assistance in a lower temperature; effectively reduces the dosage of the oxidant by controlling the product degree of polymerization distribution in a low reaction temperature; avoids using organic solvent, reduces the product costs and saves the cost by nanofiltration film separation technique and spary drying technique which can be achieve the industry mass production. Therefore, the method has a practical application value.