Structural characterization, antioxidant activity and bioaccessibility of luteolin-gellan gum covalent complex via free radical-induced coupling.

Luteolin is a bioactive flavonoid with strong antioxidant activity, however, its applications are severely limited by poor water solubility, low chemical stability, and inadequate oral bioavailability. To address these challenges, this study aims to develop a covalent delivery system capable of simultaneously enhancing both the antioxidant capacity and bioavailability of luteolin. When 0.6 g of gellan gum contains 80 mg of luteolin (GL-80), the GG-LUT composite exhibits the highest LUT encapsulation efficiency of 31.20%. With a particle size of 1.84 μm. The turbidity of the GG-LUT complex was correspondingly lower compared to pure LUT. The covalent interaction between GG and LUT was evidenced by Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (1HNMR) spectra, while ultraviolet-visible (UV-Vis) spectroscopy and X-ray diffraction (XRD) provided supporting evidence for complexation and structural rearrangement. Compared with free LUT, the GG-LUT complex exhibited superior antioxidant activity: DPPH radical scavenging rate reached 83.27%, ABTS scavenging rate reached 72.22%, and reducing power was 0.11. Moreover, the conjugate achieved a luteolin bioaccessibility of 59.46% after simulated gastrointestinal digestion, significantly higher than that of free LUT. This study provides novel methodological insights for improving the antioxidant properties and bioavailability of LUT.