Biosynthesis of levan from sucrose using a thermostable levansucrase from Lactobacillus reuteri LTH5448

Levan, a versatile fructan, possesses promising prospects for application in the food and pharmaceutical industries and in many other fields due to the superior physicochemical properties and physiological functions of this fructan. In this study, a thermostable levansucrase was identified from Lactobacillus reuteri LTH5448. This enzyme shared higher identity with reported inulosucrases than levansucrases but, unexpectedly, yielded a levan-type fructan. Structural analysis of the produced polysaccharide revealed that the glycosidic bonds were β-(2, 6) linkages, and the average molecular weight was 3.924×10⁷Da under optimized conditions. The optimal pH and temperature for levan formation were 6.0 and 35°C, respectively. The total activity was enhanced to 135% in the presence of Ca²⁺. After optimizing the production of levan, 13U/g sucrose of levansucrase and 500g/L sucrose were utilized to obtain 183g/L levan after a 12-h reaction.