Production of guluronate oligosaccharide of alginate from brown algae Stypocaulon scoparium using an alginate lyase

The brown alga Stypocaulon scoparium, collected from the Mediterranean coast of Algeria in the Bejaia region, was chosen as a model to study its alginate. This polysaccharide was extracted and characterized by HPAEC-PAD, SEC-MALLS, 1H-NMR spectroscopy and FT-IR. The ratio of D-mannuronate to L-guluronate (M/G ratio) in the alginate was 0.92 in FTIR spectra at bands of 815 and 900 cm−1 for mannuronic acid (ManA) and guluronic acid (GulA), respectively, which was comparable to alginate of other brown algae, and 0.73 with 1H-NMR spectroscopy. Complete acid hydrolysis of alginate using the HPAEC technique showed the composition of the two main acid sugars as GulA (G) and ManA (M) with an M/G ratio of 0.6, and 50 % yield. The Mw value for S. scoparium was 2.236 × 105 g mol−1, and polydispersity index Ip = Mw/Mn =1.714 ± 0.039, which was similar to that of other brown alga samples identified and cited. Partial acid hydrolysis of the alginate gave three fractions, which were characterized. Thus, the alginate sample from S. scoparium was very rich in guluronic block (G-blocks) structures (43.53 %). The guluronic blocks were degraded with poly-guluronate lyase from Flavobacterium multivorum to oligoguluronate via a β-elimination reaction, with Mw = 3.742 × 103 g mol−1.