Distribution of phenolic compounds in seed coat and cotyledon, and their contribution to antioxidant capacities of red and black seed coat peanuts (Arachis hypogaea L.)

• Predominant phytochemicals distributed in seed coats of black and red peanuts.
• Seed coats possessed much higher antioxidant capacities than cotyledons.
• Seed coats predominantly contributed phytochemicals.
• Seed coats predominantly contributed antioxidant activities of whole beans.
• MAC of black seed coat was significantly higher than that of red seed coat.
• MAC strongly correlated with the color of seed coat.

Four varieties of black and two varieties of red seed coat peanuts of different Chinese origins were examined for their total phenolic content (TPC), total flavonoid content (TFC), condensed tannin content (CTC) and monomeric anthocyanin content (MAC) in whole kernel, seed coat and cotyledon using colorimetric methods. Antioxidant activity of the separated components for each variety was determined utilizing DPPH scavenging capacity and ferric reducing antioxidant power (FRAP) assay. Contribution rates of the separated components were calculated for each parameter. It was observed that in all the six varieties, most of the phytochemicals and antioxidant activities were predominantly contributed by the seed coat followed by the whole kernel and then cotyledon. Boiling led to significant (p < 0.05) losses in the phytochemical content and antioxidant capacity. The average MAC value for the black seed coat was significantly (p < 0.05) higher than that observed for the red seed coat.