Biochemical diversity of macroalgal cell walls: Insights into the polysaccharide matrix

Macroalgal cells are surrounded by cell walls rich in polysaccharides. Beyond their scientific interest, these extracellular matrices serve as valuable sources for industrial products, such as gelling agents. This study examined the cell wall diversity across a wide array of species from three major taxonomic groups of macroalgae: green, red and brown. Alcohol-insoluble residues isolated from 11 species revealed clear taxonomic clustering based on FTIR-spectroscopy-based fingerprints. Subsequently, in-depth biochemical characterisations were carried out on four representative taxa: Ulva (green), Porphyra (red), Undaria and Himanthalia (brown). Polysaccharides were the dominant matrix component, followed by proteins. Cellulose was detected in small proportions, exhibiting variable crystallinity. Elemental analysis confirmed the presence of calcium and sulphur in considerable amounts, further supporting the detection of sulphated and ionically cross-linked polysaccharides. Chemical fractionation of the cell wall and subsequent monosaccharide analysis revealed a high compositional heterogeneity. Considering the monosaccharide composition, the structural motifs of the typical polysaccharides found in macroalgae, such as ulvan, carrageenan, fucoidan and alginate, were inferred. Overall, this work highlights the diversity and complexity of macroalgal cell wall glycans, providing a reproducible methodology for their extraction, analysis and classification. • The diversity of extracellular matrices of marine macroalgae is extraordinary. • FTIR spectroscopy coupled to multivariate analysis is a very powerful approach to track cell wall diversity. • Polysaccharides are the dominant matrix component, followed by proteins. • Cellulose is present in small proportions, exhibiting variable crystallinity. • Detailed compositional analyses revealed species-specific monosaccharide profiles.