Investigating the Core Structure of Reuteran with High-Content Linear (α1 → 6) Linkages Synthesized by <i>Limosilactobacillus mucosae</i> L24-B GtfB-Type Glucanotransferase

Reuteran is a functional homopolysaccharide comprising major (α1 → 4) and interspersed (α1 → 6) linkages whose properties and functions are directly associated with the structure. In order to enrich the structural variety and application prospects of reuteran, a GtfB-type 4,6-α-glucanotransferase from <i>Limosilactobacillus mucosae</i> L24-B (LmGtfB), which can synthesize reuteran with high-content linear (α1 → 6) linkages, was screened. LmGtfB exhibited 4,6-α-glucanotransferase activity against starch or dextrin and can synthesize both linear and branching (α1 → 6) linkages, which offered advantages in terms of source and cost. The as-produced reuteran had the highest content of linear (α1 → 6) linkages (19% in the methylation result) among the reuterans synthesized by other GtfB-type 4,6-α-glucanotransferases. A purification method was established and applied to the extraction of the core structure of the LmGtfB products. ¹H NMR and enzymatic hydrolysis revealed that the core structure contains 46.24% (α1 → 6) linkages and alternating (α1 → 4)/(α1 → 6) linkages, which was formed by enzymatic transfer of maltose.