Enzyme-Assisted Ultrasound Extraction of Bioactive Compounds from Ziziphus jujuba Mill. cv. ‘Junzao’ Fruits: Untargeted Metabolomic Profiling Reveals Enhanced Antioxidant Capacity

Enzyme-assisted ultrasound extraction offers a synergistic dual-disruption strategy, yet its differential effects on the jujube metabolome and antioxidant capacity have not been systematically characterized. This study compared ultrasound-assisted extraction (UAE) alone (N), pectinase-assisted UAE (G), cellulase-assisted UAE (X), and composite enzyme-assisted UAE (GX) for metabolite recovery from Ziziphus jujuba Mill. cv. ‘Junzao’ fruits using untargeted metabolomics and multiple antioxidant assays. The GX group exhibited the highest total phenolic content (33.42 ± 0.73 mg GAE/g DW) and total flavonoid content (7.70 ± 0.18 mg RE/g DW), significantly exceeding those of the control (N). Untargeted metabolomic profiling annotated 839 metabolites classified into 16 chemical superclasses, with lipids and lipid-like molecules, amino acids and derivatives, and organic acids and derivatives being the most abundant categories. Multivariate analysis confirmed clear compositional separation between the enzyme-assisted groups and the control, with 107 differentially extracted metabolites (DEMs) identified across the three pairwise comparisons based on extraction efficiency differences. The GX group consistently showed the strongest antioxidant activity in 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), and hydroxyl radical scavenging assays, and eight metabolites with significantly higher extraction yield showed significant positive correlations with multiple antioxidant indices in Spearman correlation analysis. These findings demonstrate that composite enzyme-assisted UAE achieved superior metabolite coverage and antioxidant potency through synergistic cell-wall deconstruction, providing a metabolomic framework for the green extraction of bioactive compounds from jujube fruits; however, further targeted validation is warranted.