Abstract: The total phenols, total flavonoids contents and in vitro antioxidant activities of petroleum ether (PE), ethyl acetate (EE) and n-butanol (BE) soluble fractions from the ethanol extract of sunflower stalk pith were evaluated and correlated with each other. Results showed that EE contained the highest amount of total phenols (1.60 ± 0.10) mg/g calculated as gallic acid equivalent and total flavonoids (20.50 ± 1.55) mg/g calculated as rutin equivalent. EE also had the highest antioxidant activity among three extracts, with half maximal inhibitory concentration of (2.56 ± 0.10) mg/mL, (52.00 ± 1.97) μmol/g and (120.57 ± 0.74) μmol/g for 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, 2,2’-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity and total reducing power (the latter two were calculated as Trolox equivalent), respectively. The correlation analysis showed that for all three extracts, there were significant correlations between the contents of total phenols and total flavonoids and DPPH and ABTS radical scavenging activity and ferric reducing antioxidant power (P < 0.01).

Key words: sunflower stalk pith, total phenols, total flavonoids, antioxidant activity, correlation analysis