Biosynthesis of oligodextrans with different Mw by synergistic catalysis of dextransucrase and dextranase

•Different adding times of dextranase on dextran sucrase system were investigated.•Oligodextrans composed of α-1,6-glycosidic linkages and low α-1,3-glycosidic branch.•P. aculeatum dextranase preferentially degraded dextran with higher molecular weights.•COSY and HSQC spectra clearly showed the internal HH and CH correlations. In this study, we have investigated various adding times of dextranase to the dextransucrase system to reveal the synergistic process of dextransucrase and dextranase. Dextranase added into the dextransucrase–sucrose system at different times gave rise to different main dextran products. The results showed that dextranase added into sucrose system at the same time with dextransucrase synthesized low molecular weight (Mw) dextran targeted to 5kDa, while dextranase added during the reaction process of dextransucrase directionally prepared dextran with medium Mw of 10kDa and 20kDa. Fourier-transform infrared (FTIR) spectroscopy and 1H Nuclear magnetic resonance (NMR) exhibited that the synthesized oligodextrans were mainly composed of α-1,6-glycosidic linkages (dextran 6587Da, 96.82%; dextran 22,521Da, 96.03%) and low α-1,3-glycosidic branch. The research established the relationship between the synergistic catalysis of the double enzymatic system and the synthesis of oligodextrans with different Mw.