The antioxidant and free radical scavenging activities of processed cowpea (Vigna unguiculata (L.) Walp.) seed extracts

The antioxidative properties and total phenolic contents of two varieties of cowpea (Vigna unguiculata  ) were examined. The raw, dry heated and hydrothermal treated samples were extracted with 70% acetone and the extracts were freeze-dried. The unprocessed light brown seeds (LB) contained significantly higher level of total phenolics and tannins than the dark brown seeds (DB). The extracts were screened for their potential antioxidant activities using tests such as O2-, OH, α,α-diphenyl-β-picrylhydrazyl (DPPH), ABTS+, FRAP, linoleic acid emulsion and β-carotene–linoleic acid in vitro model systems. At 800 μg of extract in the reaction mixture, the superoxide anion radical scavenging activity was found to be significantly higher in the raw and dry heated seed extracts than the hydrothermally processed seed samples of the respective varieties. The DPPH radical and ABTS cation radical scavenging activities were well proved and correlated with the ferric reducing antioxidant capacity of the extracts. Interestingly, among the various extracts, dry heated samples of LB and DB showed the highest hydroxyl radical scavenging activity of 83.6% and 68.2%, respectively. All extracts exhibited good antioxidant activity (74.3–84.6%) against the linoleic acid emulsion system. Using the β-carotene method, the values were significantly lower than BHT, BHA and Trolox. Owing to this property, the studies can be further extended to exploit not only the phenolic extracts but also the residual phenolic constituents associated with processed seed samples as health supplements and nutraceuticals.