Nutritional composition, mineral content, and antioxidant activity of leaf, fruit, and stem bark of Rhamnus prinoides

Rhamnus prinoides L’Hér. (Gesho) is an indigenous Ethiopian plant widely used in traditional beverages, food flavoring, and ethnomedicine; however, comparative information on the nutritional composition and antioxidant potential of its different anatomical parts remains limited. This study compared the proximate and mineral compositions of the leaf, fruit, and stem bark and evaluated the total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity of their respective 70% aqueous ethanol extracts. Proximate and mineral compositions were determined using standard AOAC methods. TPC and TFC were quantified using Folin–Ciocalteu and aluminum chloride colorimetric assays, respectively, while antioxidant activity was assessed by the DPPH radical scavenging assay (IC₅₀) and ferric-reducing power. Data were analyzed using one-way analysis of variance (ANOVA) followed by post-hoc multiple-comparison tests ( p < 0.05). Extraction yield was highest in the fruit (25.48 ± 1.00 mg/g) and leaf (24.66 ± 2.09 mg/g) and lowest for the stem bark (13.98 ± 0.30 mg/g). On a raw biomass basis, stem bark had the highest crude fiber (59.52%) and crude protein (9.96%) contents, whereas fruit exhibited the highest crude fat content (11.67%). The leaf had the highest carbohydrate (60.6%) and ash (10.40%) contents. Among the extracts, the leaf exhibited the highest TPC (48.44 mg GAE/g) and TFC (18.78 mg CE/g). Despite its lower TPC and TFC than the leaf, the stem bark exhibited the strongest DPPH radical-scavenging activity, with the lowest IC₅₀ value (48.01 µg/mL). This difference indicates that antioxidant activity was not explained solely by the total concentrations of phenolic and flavonoid compounds. Differences in the composition and relative activity of individual phytochemicals or interactions among antioxidant constituents may contribute to this response; however, these possibilities remain hypothetical because individual compounds were not characterized in the present study. Chromatographic and mass-spectrometric profiling is therefore required to elucidate the chemical basis of the observed tissue-specific antioxidant activity. Antioxidant capacity followed the order stem bark > leaves > fruit, with strong exploratory associations between phenolic/flavonoid contents and antioxidant measurements. These findings provide a comparative nutritional and functional profile of different anatomical parts of R. prinoides and support their potential as a source of natural functional ingredients, while further characterization is required to establish their specific bioactive constituents.