Physicochemical characterization of glucan AK7 produced by quinoa sourdough isolate Leuconostoc mesenteroides AK7

The production of exopolysaccharides (EPS) by Lactic Acid Bacteria (LAB) is technologically crucial because it has a wide range of applications in food technology, biotechnology, and health. In the present work, a new quinoa sourdough isolate of Leuconostoc mesenteroides strain AK7 was identified as a novel producer of a dextran-type EPS. The monomeric units of EPS AK7 were confirmed by HPLC analysis, while NMR spectroscopy and GC-MS linkage analysis further verified the EPS structure as a branched dextran containing mainly (1 → 6)-linked α- D -glucose units with (1 → 3,6)-linked α- D -glucose unit as branching points. An average molecular weight of 1.2 × 10⁶ Da was detected for glucan AK7. FTIR analysis was applied to determine the functional units of dextran AK7. In terms of thermal features, TGA and DSC analysis were applied and a specific degradation temperature of 300 °C was found for dextran AK7. The morphology of the lyophilized EPS displayed a rough, dense, and porous structure, as observed through SEM analysis. Dextran AK7 revealed a semi-crystalline nature detected by XRD analysis. These structural and functional properties of dextran AK7 produced by Leuconostoc mesenteroides AK7 from quinoa sourdough suggest its potential usage for food industry applications.