Site-Dependent Variation in Phenolics and Antioxidant Capacity of Berberis vulgaris Raw Materials: A Multi-Assay Study

Plant phenolics are increasingly explored as natural antioxidants for food systems, yet antioxidant capacity data are difficult to compare because assay chemistry and geographic origin can influence outcomes. Moreover, conventional solvent-based assessments may underestimate the contribution of non-extractable phenolic fractions. Here, <i>Berberis vulgaris</i> L. raw materials from six Lithuanian habitats were assessed using hydrolyzed extracts to estimate total releasable phenolics following hydrolytic treatment: total phenolic content (Folin-Ciocalteu) and antioxidant capacity (FRAP, CUPRAC, ABTS, and DPPH) were measured, and fruit extracts were additionally profiled by HPLC-DAD and LC-MS. Across matrices, mean TPC was comparable (108.7 ± 14.1, 111.9 ± 8.4, and 121.9 ± 14.7 mg GAE/g DW for bark, leaves, and fruits, respectively). However, comparable bulk phenolic levels did not translate into uniform antioxidant responses across assays. In contrast, site effects were pronounced, with fruit TPC ranging from 80.0 ± 5.1 to 242.2 ± 61.0 mg GAE/g DW, indicating that geographic origin may outweigh morphological differences when bulk metrics are used. Antioxidant capacity assays further confirmed pronounced site-dependent variability. In particular, leaf extracts exhibited the largest geographic differences, with CUPRAC values ranging from 268.5 ± 32.8 to 586.2 ± 58.6 µmol TE/g DW and ABTS values ranging from 222.0 ± 43.1 to 562.9 ± 26.6 µmol TE/g DW across sampling sites, corresponding to approximately 2.2- and 2.5-fold variation, respectively. Moreover, assay-specific responses led to differences in matrix ranking: bark showed the highest FRAP reducing power (373.2 ± 15.9 µmol TE/g DW), whereas leaves exhibited the highest CUPRAC and ABTS activities (395.7 ± 46.7 and 346.6 ± 48.5 µmol TE/g DW, respectively). Chromatographic profiling of fruits revealed a structurally diverse set of phenolic acids and flavonoids, providing structural support for assay-dependent antioxidant behavior. Overall, integration of multi-assay antioxidant evaluation with hydrolysis-based phenolic assessment and chromatographic profiling provides a broader characterization of <i>Berberis vulgaris</i> as a plant matrix of interest for food applications. This integrated approach supports more context-aware interpretation of antioxidant data in applied food research.