Endo-beta-1,3-glucanase digestion combined with the HPAEC-PAD-MS/MS analysis reveals the structural differences between two laminarins with different bioactivities

To resolve the structure of laminarin, the recombinant endo-beta-1,3-glucanase from Coprinopsis cinerea, which has specific activity on beta-1,3 glycosidic bond and could hydrolyze the laminarin with complex structure, was used to hydrolyze laminarin. Then, the structures of enzyme-resistant oligosaccharides were quantitatively and qualitatively analysed by high-performance anion exchange chromatography coupled with mass spectrometry. The laminarin from Laminaria digitata contains 9.51% beta-1,6 glycosidic bonds only in the branches (branch degree 7.68%). The laminarin from Eisenia bicyclis contains more beta-1,6 glycosidic bonds: 19.42% beta-1,6 glycosidic bonds in backbone and more and longer beta-1,6 branches (branch degree 25.99%). The differences in the ratio of glycosidic bonds and branch degree influence their bioactivity: the antioxidant activity and the antimicrobial activity against Gram positive bacteria of the laminarin from E. bicyclis is stronger than the laminarin from L. digitata, but the antimicrobial activity on Gram negative bacteria of the laminarin from E. bicyclis is weaker.