Phenolic Profile and Antioxidant Activity of Brown and Yellow Varieties of Tigernut (<i>Cyperus esculentus L.</i>)

Abstract

Tigernut is a sedge with tuber planted and consumed in Nigeria but with no documented phenolics profile. This work determined the phenolic profile and the antioxidant activity of tigernut tubers grown and consumed in Nigeria. Tigernuts (yellow, YTG and brown, BTG)) were sorted, washed, dried, milled into powder, phenolics extracted with sodium hydroxide and analyzed with Gas chromatography (GC). The tigernuts contain significant concentration of hydroxybenzoic acids, hydrocinnamic acids and flavonoids. The major phenolic acids in YTG were ferulic acid (58.38 mg/ 100 g), p-hydroxybenzoic acid (29.12 mg/100 g), p-hydroxybenzaldehyde (16.47 mg/100 g) and vanillic acid (5.88 mg/ 100 g) while the major phenolic acids in BTG were vanillic (15.20 mg/100 g), p-coumaric (17.25 mg/100 g), caffeic (15.25 mg/100 g), ferulic (33.79 mg/100 g) and sinapinic acids (20.97 mg/100 g). Ferulic acid concentration was highest in the two samples. The concentration of the flavonoid compounds in YTG and BTG followed the same trend: flavones (52, 81%) > flavonols (36, 19%) > flavanones (7, 0%) > flavanols (5, 0%) > isoflavones (0, 0%). The 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) values were 86.20% and 37.5% (YTG) and 38.30% and 42.8% (BTG).

Keywords: Tigernut, phenolic profile, flavonoids, antioxidant activity