Extraction, structural characterization, and bioactivity of laminarin and fucoidan from brown macroalgae Chorda filum

The present study investigates the structural characterization and bioactivity of macroalgal polysaccharides (laminarin and fucoidan) extracted and purified from Chorda filum collected from Kongsfjorden, Arctic. The extraction was done using a hydrothermal-assisted extraction method followed by purification using ion exchange and size-exclusion chromatography. Two purified fractions, Chorda purified fraction (CPF) 1 (neutral) and CPF 2 (anionic), were obtained and examined for their bioactivity and chemical characterization. The major fraction CPF1 displayed notable free radical inhibition activities: 1, 1-diphenyl-2-picryl-hydrazyl (IC₅₀ 5.21 ± 0.24 mg mL⁻¹), 2, 2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (IC₅₀ 3.28 ± 0.04 mg mL⁻¹), and hydrogen peroxide (IC₅₀ 3.06 ± 0.12 mg mL⁻¹). It also exhibited strong α-glucosidase enzyme inhibition activity (IC₅₀ 0.125 ± 0.012 mg mL⁻¹), equivalent to the model commercial compound acarbose. Fourier-transform infrared (FTIR) analysis of CPF1 indicated O–H, C–H, CO, C–C, and C–O stretching, reflected by peaks at 3335 cm⁻¹, 2919 cm⁻¹, 1369 cm⁻¹, 1100 cm⁻¹, and 1030 cm⁻¹, respectively. The monosaccharide composition CPF1 revealed a major composition of glucose with mannitol residues. The 1H Nuclear magnetic resonance (NMR) peaks at δ 3.3–3.6 ppm, δ 3.5–3.7 ppm, δ 3.6–3.9 ppm, δ 4.3–4.5 ppm, δ 4.6–4.8 ppm and δ 5.1–5.3 ppm and 13C NMR spectrum peak at δ60.66, 68.08, 73.28, 75.60, 84.11, and 102.5 ppm corresponded to C6, C4, C5, C2, C3, and C1 of m-type β-(1, 3)-glucan structure. The molecular mass of CPF1 using gel permeation chromatography (GPC) was found to be approximately 64 kDa. In summary, CPF1, a bioactive, m-type laminarin, was successfully extracted and purified from the understudied filamentous macroalgae C. filum.