From agricultural waste to antioxidant resource: pectinase hydrolysis unlocks the bioactive potential of Glycyrrhiza uralensis Fisch

Glycyrrhiza uralensis Fisch. ( G. uralensis ) leaves are an abundant agricultural residue containing polysaccharides and phenolic compounds, but their extraction is limited by the compact plant cell-wall matrix. This study applied pectinase-assisted solid-state processing to enhance the extraction and functional properties of bioactive compounds from G. uralensis leaves. Compared with the non-enzymatic control (GLP), the enzymatically treated product (EGLP) showcased higher soluble polysaccharide content, increasing from 266.06 ± 1.58 to 319.40 ± 4.19 mg/g, and higher total polyphenol content, increasing from 59.47 ± 0.63 to 63.99 ± 0.81 mg/g. FT-IR spectroscopy detected cleavage of glycosidic and pectic ester bonds, while monosaccharide profiling showed an increase in galacturonic acid from 3.49% to 5.87%, indicating preferential degradation of pectic domains. Untargeted metabolomics identified 892 differentially expressed metabolites (DEMs) between EGLP and GLP, with glycosides representing a major altered class. Several glucoside metabolites, mainly flavonoid-related glycosides, showed increased relative abundance and were positively correlated with galacturonic acid content and antioxidant indices. In vitro assays revealed superior radical-scavenging and reducing capacities of EGLP, while in the AAPH-induced zebrafish oxidative stress model, EGLP at 50 µg/mL offered greater protection than GLP, as indicated by improved body length, reduced yolk-sac enlargement, and normalized developmental progression. SEM, XRD, TGA and hydration-property analyses further supported cell-wall loosening, reduced structural order, and improved solubility after enzymatic treatment. Molecular docking based on a representative endopolygalacturonase model revealed stable binding of 7 key glycosides to pectinase (binding energies ≤ − 7.9 kcal/mol, 6–12 hydrogen bonds). Pectinase-mediated processing integrated cell-wall disassembly with flavonoid glycoside enrichment, significantly enhanced antioxidant properties, and provided green technological support for the high-value utilization of G. uralensis leaf waste.