Fucoidan from sea cucumber cooking liquid: Structural analysis, physicochemical properties, and anti-Helicobacter pylori potential.

Helicobacter pylori (H. pylori) is a major pathogen implicated in chronic gastritis, peptic ulcers, and gastric cancer. The increasing prevalence of antibiotic resistance and biofilm-associated persistence necessitates alternative therapies. This study aimed to investigate the inhibitory effect of fucoidan (Fuc) from sea cucumber cooking liquid (Fuc-SC) on H. pylori. Fuc-SC, with a molecular weight of 6.75 kDa, comprises 65.94 % fucose and 31.69 % sulfate group. Structural analysis revealed that Fuc-SC was a branched sulfate fucoidan with a backbone of →3)-α-L-Fucp-(1 → 4)-α-L-Fucp-(1→, featuring sulfate groups at C-4 of →3)-α-L-Fucp-(1→ and C-2 or C-3 of →4)-α-L-Fucp-(1→, alongside branches containing fucose, galactose, and glucose. The rare sulfation and branching pattern broaden the structural diversity of Fuc from sea cucumber. AFM analysis revealed that Fuc-SC exhibits an irregular linear chain conformation, while SEM analysis showed a porous sheet structure. The average particle size of Fuc-SC was 36.5 μm, demonstrating outstanding thermal stability within the temperature range of 30-200 °C. Viscosity analysis indicated that the viscosity of Fuc-SC increased with mass concentration and decreased with temperature, displaying shear-thinning behavior typical of hydrocolloids. In vitro antioxidant activity revealed that Fuc-SC exhibited stronger ABTS and DPPH radical scavenging capacities and a higher total antioxidant capacity compared to Laminaria japonica-derived fucoidan (Fuc-LJ). Additionally, Fuc-SC demonstrated a significant inhibition zone against H. pylori Sydney strain 1 (Hp SS1). Notably, Fuc-LJ and desulfurized Fuc-SC did not exhibit a bacteriostatic ring. Fuc-SC also decreased Hp SS1 adhesion by inhibiting urease activity. Furthermore, it protected GES-1 cells from ROS-induced mitochondrial damage and apoptosis by disrupting bacterial structure and inhibiting biofilm formation. The findings highlight its potential for development as a dietary supplement and specialty medical food for the treatment of H. pylori gastrointestinal diseases.