Degradation Behavior and Mechanism of Agar Polysaccharides Induced by Hydrogen Peroxide: Structure Evolution and Bioactivity of Oligosaccharides

Although H2O2-mediated degradation efficiently yields bioactive oligosaccharides, the underlying mechanisms and structure–activity relationships (SARs) of agar polysaccharides remain elusive. Here, the H2O2 degradation profiles of agar (FA) and agarose (TA) were systematically compared using HRMS/MS and 2D NMR. FA products underwent extensive hydrolytic ring-opening at 3,6-anhydro bridges, whereas TA products predominantly retained intact anhydro skeletons. In LPS-induced RAW 264.7 macrophages, intact TA oligosaccharides potently inhibited TNF-α and IL-6 secretion, whereas ring-opened FA oligosaccharides lost anti-inflammatory activity and triggered pro-inflammatory responses. This study elucidates the specific SAR of agar polysaccharides and identifies 3,6-anhydro-l-galactose as the essential anti-inflammatory pharmacophore, offering a robust theoretical basis for the targeted green preparation of bioactive marine oligosaccharides.