In vitro antioxidant activity and polyphenolic content of commonly used spices from Ethiopia

Introduction: In this study, the antioxidative effectiveness, and polyphenolic content of methanol and aqueous extracts of spices such as Lippia adoensis (Koseret), Nigella sativa (Thikur azmud), Piper capense (Timiz), Thymus schimperi (Tosign) and Trachyspermum ammi (Netchazmud), consumed among people of Ethiopia were investigated.

Methods: The antioxidant activity was assessed via established in vitro assay models such as 2, 2-Diphenyl-1-Picrylhydrazyl (DPPH) radical quenching assay, reducing power assay and reactive nitrogen species (RNS) inhibitory potential. Total phenolics content was measured according to Folin-Ciocalteu's method and total flavonoid content was estimated by using Aluminium chloride colorimetric method.

Results: The results showed that the total phenolic content was highest in both methanol (720 ± 0.04 mg GAE/100 g extract DW) and aqueous (580 ± 0.08 mg GAE/100 g DW) extracts of L. adoensis. Among the five tested spices, the methanol and aqueous extracts of L. adoensis exerted the strongest DPPH radical quenching activity with IC₅₀values of 49.17 ± 1.26 and 20.99 ± 8.6 μg/mL, respectively. Both methanol and aqueous extracts of L. adoensis showed notable reducing capacity. The highest RNS scavenging activity was shown by both methanol (IC₅₀ 597.21 ± 6.99 μg/mL) and aqueous (IC₅₀ = 551.5 ± 28.9 μg/mL) extracts of L. adoensis. High to moderate positive correlations were observed between total phenolic contents and in vitro antioxidant assays. This indicates that the antioxidant activities of the tested spices are attributed to the phenolic contents.

Conclusion: The results of the present work revealed that the tested spices demonstrated high phenolic contents and antioxidant properties. Thus, these spices are worth considering as important sources of natural antioxidant agents.

Keywords: Antioxidant activity; DPPH; Food analysis; Food science; RNS; Spices; Total flavonoids; Total phenolics.