A method for preparing k-potassium carrageenan having a low molecular weight by means of enzymolysis, comprising the following steps: (1) preparing a k-carrageenan aqueous solution having a mass concentration of 0.5-1.5% from k-carrageenan powder in a 40-50°C water bath kettle, stirring uniformly, adding k-carrageenanase, and stirring for enzymolysis for 6-8 h; (2) subjecting an enzymatic hydrolysate to alcohol precipitation to obtain k-carrageenan oligosaccharide having a low molecular weight; and (3) preparing a solution having a mass concentration of 4-10% from the obtained k-carrageenan oligosaccharide, mixing the solution with a potassium chloride aqueous solution having a mass concentration of 0.1-2%, and subjecting the mixed solution to alcohol washing and salt removing to obtain k-potassium carrageenan having a low molecular weight. The method has simple steps and mild conditions; the molecular weight of prepared k-potassium carrageenan having a low molecular weight is stabilized within a small range; and the potassium ion binding rate is high. K-potassium carrageenan can be added into food as a food additive to obtain healthcare products, and can also be prepared into medicines as drugs for preventing or treating hypertension.
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