Antioxidant activity and mechanisms of low-molecular-weight oxidized konjac glucomannan prepared by a sequential modification strategy.

To elucidate the relationship between structural modifications and bioactivity in konjac glucomannan (KGM) derivatives, this study developed a "degradation-oxidation" sequential modification strategy to overcome the intrinsic bioactivity limitations of native KGM. Using low-molecular-weight degraded KGM (DKGM-5k) as the precursor, we synthesized a series of oxidized derivatives (ODKGMs) with controlled oxidation degrees (30%, 50%, and 90%) via the (2,2,6,6-tetramethylpiperidin-1-yl) oxyl (TEMPO)/NaClO/NaBr system. Structural analysis combined with in vitro antioxidant assays identified 50% oxidation degree as optimal for enhancing the radical-scavenging capacity of degraded KGM. Subsequent DEAE-52 cellulose chromatography yielded three homogeneous fractions, among ODKGM-50%-0.2 M exhibited the most potent cytoprotective effects by activating the Keap1/Nrf2/ARE signaling pathway. Methylation analysis confirmed that ODKGM-50%-0.2 M retains the β-1,4-glycosidic backbone, with TEMPO-mediated oxidation selectively targeting the C6 primary hydroxyl groups. These structural features, together with the degree of oxidation, appear critical for the observed cellular bioactivity. However, the present findings are limited to in vitro models, and the precise molecular interactions between ODKGM-50%-0.2 M and the Keap1-Nrf2 complex remain to be verified. Collectively, this study provides a scientific basis for the rational design of bioactive polysaccharide-based antioxidants and positions ODKGM-50%-0.2 M as a promising candidate for functional food and biomedicine applications; its in vivo efficacy and mechanism will be investigated in future studies.