High-resolution Molecular Fingerprinting of Algal Polysaccharides Extracted at Alkaline Hydrothermal Conditions

Alkaline hydrothermal water extraction was applied to macroalgae Ascophyllum nodosum (A. nodosum) and microalgae Arthrospira platensis (A. platensis) to separate alginate-like polysaccharides and evaluate their structural integrity. A multidimensional analytical workflow combining solution-state ¹H NMR, solid-state ¹³C CP/MAS NMR, and ultrahigh-resolution FT-ICR-MS (ESI and GALDI) was established to bridge polymer backbone analysis with molecular-level fingerprinting. NMR analyses indicated the retention of characteristic glycosidic and carboxyl-associated functionalities in A. nodosum, whereas corresponding signals were absent in A. platensis, indicating fundamental compositional differences. FT-ICR-MS resolved up to 1591 molecular formulas, revealing high extract complexity dominated by lipid-like and hydrocarbon species, while carbohydrate-assigned formulas were comparatively underrepresented due to limited ionization efficiency. Nonetheless, the presence of oxygen-rich compounds in the macroalgal residue sample supported the presence of alginate-related molecules. The combined approach demonstrates the complementary strengths of NMR and FT-ICR-MS for process monitoring, structural verification, and molecular fingerprinting of complex algal extracts, advancing analytical strategies for sustainable polysaccharide valorization.