The total polysaccharide content of the sugar-rich filamentous microalga Tribonema minus (Xanthophyceae, Tribonematales) under 2% CO 2 was up to 50%. The optimal conditions for the extraction of polysaccharide by hot water extraction-ethanol deposition were as follows: A maximum polysaccharide yield of 27.25% was obtained under the optimized conditions of extraction temperature 80°C, extraction time of 2 h, pH 9, and liquid to raw material 0.5:1 mL mg −1 . The crude polysaccharides were mainly acidic polysaccharides containing sulfate groups and uronic acid, and the contents of which were 14.57% and 42.21 mg g −1 , respectively. The crude polysaccharide was mainly composed of rhamnose, arabinose, xylose, mannose, glucose, and galactose with a molar ratio of 0.31:0.26:0.40:0.42:1.00:0.47. In addition, the polysaccharide had a potential antioxidant activity in vitro. The scavenging effect and reducing power of polysaccharides increased with the increase of polysaccharide concentration. The scavenging effect was 56.11%, 75.6%, and 61.89% for 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH), superoxide, and hydroxyl radicals at a concentration of 2 mg L −1 , respectively. Hence, T. minus polysaccharides could be a source of natural antioxidants that might be used in foods or pharmaceuticals.
Tribonema polysaccharide (TP), a biologically active polysaccharide containing β-1,3-glycosidic bonds, has not been extensively studied as a dispersing agent for stabilising selenium nanoparticles (SeNPs), and its synergistic effects with SeNPs remain poorly understood. This study investigates the relationship between the antioxidant activity and physicochemical properties of TP–SeNPs, which were synthesised through chemical reduction at varying TP-to‑selenium mass ratios (TPSMRs). TP was isolated from Tribonema minus using ultrasonic-assisted extraction, achieving a 119.64 % increase in yield under optimal conditions (400 W, 25 min, 1:400 solid-to-liquid ratio). Structural analysis identified TP as a novel β-1,3-glucan (8.46 kDa) composed exclusively of glucose units. Moreover, TP–SeNPs prepared at varying TPSMRs exhibited significantly higher antioxidant activity than either TP or SeNPs alone, demonstrating a clear synergistic effect. Notably, TP–SeNPs prepared at a TPSMR of 2:3 exhibited the lowest half-maximal inhibitory concentrations for scavenging 2,2-diphenyl-1-picrylhydrazyl, superoxide anions, and hydroxyl radicals (0.30, 0.77 and 0.46 mg/mL, respectively). This was attributed to the increased selenium content and reduced particle size of these complexes. Additionally, TP–SeNPs displayed excellent dispersibility and stability, likely due to non-covalent interactions between TP and SeNPs. In cellular assays, TP–SeNPs exhibited low cytotoxicity and dose-dependently enhanced cell viability under H 2 O 2 -induced oxidative stress. Cells treated with 200 mg/L TP–SeNPs exhibited a 35.83 % increase in viability compared with the model group. This protection was associated with elevated antioxidant enzyme activity, increased glutathione levels and reduced malondialdehyde content, thereby mitigating oxidative damage in HepG2 cells. This study is the first to characterise a novel β-1,3-glucan from T. minus and to elucidate the structure–activity relationships of TP–SeNPs, highlighting their potential as functional additives or pharmaceutical supplements.
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