Phytochemical Investigation and Antioxidant Mechanisms of Extracts from Anacardium occidentale Bark in Enugu State

Anacardium occidentale, commonly known as cashew, has been used in ethnomedicine across South East Nigeria for the treatment of inflammation, diabetes, and infectious diseases, yet the specific antioxidant mechanisms underlying its biological activity and the identity of responsible bioactive constituents from Enugu State specimens have not been fully characterised. This study investigated the phytochemistry, antioxidant activity, and mechanistic basis of antioxidant action of successively extracted fractions of Anacardium occidentale stem bark. Bark was collected from three farms in Enugu State and extracted with hexane, ethyl acetate, methanol, and water. Qualitative and quantitative phytochemical profiling was conducted. Antioxidant activity was assessed using DPPH, ABTS, FRAP, hydrogen peroxide scavenging, and superoxide radical scavenging assays. The role of specific compound classes in antioxidant activity was investigated by selectively depleting phenolics, flavonoids, and tannins and comparing residual activity to intact extracts. Eight isolated flavonoid compounds were characterised by nuclear magnetic resonance and mass spectrometry. Total phenolic and flavonoid content strongly correlated with antioxidant activity across all assays. Anacardic acid was the dominant hexane extract constituent and demonstrated potent superoxide inhibition. Quercetin, rutin, and catechin were identified as major contributors to the methanol extract antioxidant activity. Tannin depletion caused the greatest proportional reduction in FRAP values, indicating tannins as primary ferric-reducing antioxidants. These mechanistic insights go beyond previous descriptive antioxidant studies and provide target compound information for further nutraceutical development using Enugu State cashew bark.

Keywords: Anacardium occidentale, antioxidant mechanism, phenolics, Enugu State, phytochemical investigation