Dextrans produced by Leuconostoc isolates from sugarcane factories: Potential impact on viscosity during sugarcane processing.

Abstract

Exopolysaccharides (EPS) from factory-derived Leuconostoc isolates were evaluated to determine impacts on sugarcane processing and to explore EPS production by these strains. Two isolates, L. suionicum LASM7 and L. lactis LASM16, exhibited elevated culture viscosity from increased EPS production. Samples were classified as dextrans by FTIR and NMR. Glycosidic linkage analysis identified an α-1,6 Glcp backbone with variation in side linkages. A 4-linked glucopyranosyl residue (4-Glcp) was present in L. suionicum LASM5 and L. suionicum LASM6 samples compared to negligible levels in LASM7 and LASM16. NMR indicated 4-Glcp was present on disaccharide chains on residues on dextran backbones in LASM5 and LASM6, and a minor polysaccharide component with a → 6)-β-Glcp-(1 → was observed. Conversely, LASM7 and LASM16 had higher percentages of 6-linked glucopyranosyl residues. Several glucansucrases were identified among isolate genomes. LASM5, LASM6 and LASM7 encoded Gtf1624 homolog with predicted α-1,6 dextransucrase activity, BsrA with predicted α-1,2-branching dextransucrase activity, and DsrE homolog with bifunctional α-1,6-dextransucrase/α-1,2-branching activities. LASM16 encoded a single dextransucrase with predicted α-1,6-dextransucrase activity, consistent with more linear structure. These results have important practical implications for sugarcane processing (e.g., juice filtration, sucrose crystallization) and bioproduct development (e.g., functional food additives).