Rhamnus prinoides Stem Bark Shows Highest Antioxidant Activity in Comparative Study

Stem bark of the indigenous Ethiopian plant Rhamnus prinoides exhibits the strongest radical-scavenging antioxidant activity despite containing lower total phenolic and flavonoid concentrations than the leaves, according to comparative experimental findings. The investigation examined the proximate compositions, mineral content, and functional antioxidant profiles of the leaf, fruit, and stem bark of the species, commonly known as Gesho. While the plant has seen longstanding and widespread traditional use across Ethiopia in the preparation of fermented beverages, food flavoring, and traditional ethnomedicine, comparative scientific data evaluating the nutritional and functional differences across its distinct anatomical structures had remained scarce.

To assess the biological and chemical profiles of the different plant components, researchers prepared 70 percent aqueous ethanol extracts from the harvested leaf, fruit, and stem bark biomass. Extraction efficiency varied substantially across the three anatomical tissues, registering its highest yields in the fruit material at 25.48 ± 1.00 milligrams per gram and the leaf material at 24.66 ± 2.09 milligrams per gram. In contrast, the stem bark produced a noticeably lower extraction yield of 13.98 ± 0.30 milligrams per gram. The experimental protocol employed standard Association of Official Analytical Chemists methods to determine proximate and mineral parameters, applied colorimetric procedures for secondary metabolite quantification, and utilized one-way analysis of variance with post-hoc multiple-comparison tests at a significance threshold of p < 0.05 to analyze the resulting data.

Nutritional assessments carried out on a raw biomass basis revealed clear tissue-specific distributions of macronutrients, ash, and dietary fiber among the anatomical parts. The stem bark contained the highest proportions of crude fiber and crude protein, measuring 59.52 percent and 9.96 percent, respectively. In comparison, the fruit demonstrated the highest accumulation of crude fat, recording a value of 11.67 percent. The leaf tissue was characterized by the highest carbohydrate concentration at 60.6 percent, as well as the highest ash content at 10.40 percent, highlighting distinct nutritional profiles between the vegetative tissues, reproductive structures, and outer woody bark.

Quantification of phytochemical constituents in the 70 percent aqueous ethanol extracts demonstrated that the leaves harbored the highest overall concentrations of polyphenolic compounds. The researchers determined total phenolic content using the Folin–Ciocalteu assay and total flavonoid content via the aluminum chloride colorimetric assay. Leaf extracts yielded 48.44 milligrams of gallic acid equivalents per gram of total phenolics and 18.78 milligrams of catechin equivalents per gram of total flavonoids. Although the team identified strong exploratory associations between the measured phenolic and flavonoid levels and the broader antioxidant indicators across the plant parts, higher total concentrations did not translate directly into the highest free-radical neutralization capacity.

Functional antioxidant capacity, evaluated through the 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay and ferric-reducing power measurements, followed a distinct tissue ranking of stem bark followed by leaves and then fruit. Despite its lower total phenolic and flavonoid values compared to leaf tissue, the stem bark extract demonstrated the most potent radical-scavenging capability, marked by the lowest half-maximal inhibitory concentration of 48.01 micrograms per milliliter. This marked divergence indicated that overall antioxidant effectiveness cannot be accounted for solely by the aggregate quantities of phenolic and flavonoid compounds present in the extracts.

The authors observed that differences in the specific identities and relative individual activities of distinct phytochemical constituents, or synergistic and antagonistic interactions occurring among specific antioxidant compounds, could contribute to the enhanced potency of the stem bark. However, the study emphasized that such explanations remain hypothetical because individual chemical molecules were not isolated or characterized in the present experimental work. The researchers concluded that advanced chromatographic separation and mass-spectrometric profiling will be required to determine the precise chemical basis of this observed tissue-specific antioxidant activity. Ultimately, the comparative data support the potential of Rhamnus prinoides anatomical tissues as natural functional ingredients, while further detailed characterization remains necessary to confirm their specific active constituents.

Subject of Research: Nutritional and antioxidant profile of Rhamnus prinoides anatomical parts

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

Article References: Abera, E., Ayele, Y., Dessalegn, E., & Assefa, D. (2026). Nutritional composition, mineral content, and antioxidant activity of leaf, fruit, and stem bark of Rhamnus prinoides. Discover Food. https://doi.org/10.1007/s44187-026-01302-3

Image Credits: AI Generated

DOI: 10.1007/s44187-026-01302-3

Keywords: Rhamnus prinoides, Gesho, antioxidant activity, phenolic content, flavonoids, plant nutrition, crude fiber, free radical scavenging, Nutritional, composition, mineral, content