Methodology for quantitative determination of the carbohydrate composition of brown seaweeds (Laminariaceae)

The monosaccharide composition of four different samples of brown seaweeds Laminaria digitata and Saccharina latissima were compared by different high performance anion exchange chromatography (HPAEC) methods after different acid hydrolysis treatments or a cellulase treatment. A two-step treatment of 72% (w/w) H2SO4 + 4% (w/w) H2SO4 performed best, but cellulase treatment released more glucose than acid treatments. HPAEC with pulsed amperometric detection (PAD) allowed quantification of all present neutral sugars and the sugar alcohol mannitol. Furthermore, the use of guluronic, glucuronic, and galacturonic acid as standards enabled quantification of the uronic acids. A complete map of amino acids, fatty compounds, minerals, and ash was also achieved. L. digitata and S. latissima harvested in Denmark April (Baltic Sea, 2012) were dominated by alginic acid and ash (each similar to 30% by weight (w/w) of the dry matter) and 10% (w/w) protein. In contrast, the dominant compound of L. digitata harvested in August (North Sea, 2012) was glucose constituting 51% w/w of the dry matter, and with 16% w/w alginic acid. Washing prior to analysis mainly removed salts.