High-temperature steam treatment enhances antioxidant activity in Glycyrrhiza uralensis Fisch. (G. uralensis) leaves via coordinated structural disruption and metabolic remodeling

Oxidative stress is a major pathological factor in chronic diseases, driving the need for safe and sustainable natural antioxidants. Although Glycyrrhiza uralensis Fisch. is widely utilized for its roots, its leaves (GL) remain underexploited despite being rich in polysaccharides and polyphenols. The dense and highly ordered cell wall structure of GL restricts the release and bioaccessibility of these bioactive constituents. This study aimed to evaluate whether a green high-temperature steam treatment could induce structural and metabolic remodeling in GL to enhance the release and antioxidant efficacy of its functional components. Multi-scale structural analyses revealed that steam treatment significantly disrupted the cell wall, reduced crystallinity, and decreased thermal stability, resulting in a more porous leaf matrix. Monosaccharide profiling and Fourier-transform infrared (FT-IR) spectroscopy revealed selective redistribution of monosaccharides, enrichment of uronic acids and arabinose, and attenuation of hydrogen-bonding networks without destruction of the polysaccharide backbone. Untargeted metabolomics identified 637 differentially expressed metabolites, with significant remodeling of flavonoids, phenolic acids, and glycosylated compounds, indicating coordinated secondary metabolic reprogramming. Functionally, polysaccharides from high-temperature steam-treated GL (HGL) exhibited markedly enhanced antioxidant activity, including improved 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radical scavenging, as well as increased reducing power. In vivo, HGL supplementation in an AAPH-induced zebrafish embryo oxidative stress model significantly improved survival and hatching rates, supported embryonic growth, normalized yolk sac utilization, and alleviated oxidative stress-related developmental issues in a dose-dependent manner. High-temperature steam treatment integrates structural disruption and compositional remodeling to enhance the antioxidant efficacy of GL. This approach offers a sustainable strategy for utilizing GL and emphasizes the potential of green physical processing to unlock the functional benefits of underused plant tissues.