Preparation method of high-uniformity high-molecular-weight Levan fructan

The invention discloses a preparation method of high-uniformity high-molecular-weight Levan fructan. The method comprises the following steps: carrying out molecular modification on fructosyl sucrose transferase by using modern molecular enzyme engineering to obtain a fructosyl sucrose transferase mutant H280R, successfully carrying out prokaryotic expression in Escherichia coli, purifying the expressed protein, carrying out reaction on the purified enzyme and a substrate sucrose, and carrying out ethanol precipitation to obtain the Levan fructan sample. When the fructosyl sucrose transferase mutant H280R is used for preparing the Levan fructan, the concentration of the substrate sucrose can reach 40%. Gel chromatography is utilized to determine that the molecular weight is 2*10 Da, so the Levan fructan belongs to high-molecular polysaccharides. The Levan fructan has the advantages of high uniformity and higher dispersity (2.06) than that of the Levan fructan prepared by the existing biological method. 本发明公开了