In vitro antioxidant, anti-diabetic and antilipemic potentials of quercetagetin extracted from marigold (Tagetes erecta L.) inflorescence residues.

Quercetagetin, the major flavonoid in marigold (Tagetes erecta L.) inflorescence residues was extracted and purified. The content of quercetagetin after the purification was 89.91 ± 0.26 %. The in vitro antioxidant activity of quercetagetin and its potential in controlling diabetes mellitus and obesity were investigated and compared to quercetin and rutin. The 50 % inhibitory concentration (IC50) values of quercetagetin on scavenging 1, 1-diphenyl-2-picrylhydrazyl (DPPH), 2,2-azinobis-(3-ethylbenzothiazolin-6-sulfonic acid) (ABTS) and hydroxyl radicals were 27.12 ± 1.31 μmol/L, 12.16 ± 0.56 μmol/L and 1833.97 ± 6.66 μmol/L, respectively. The IC50 values of quercetagetin on α-glucosidase, α-amylase and pancreatic lipase were 180.11 ± 3.68 μmol/L, 137.71 ± 3.55 μmol/L and 2327.58 ± 12.37 μmol/L, respectively. These results indicated that quercetagetin exhibited strong in vitro antioxidant, anti-diabetic and antilipemic activities. Lineweaver-Burk plots analysis elucidated that quercetagetin inhibited α-glucosidase and α-amylase non-competitively, while its inhibition against pancreatic lipase was involved in a mixed-type pattern. Moreover, strong correlations were found between ABTS(·+)/DPPH(·) scavenging activities and lipase inhibitory activity (R (2) > 0.90), as well as ·OH scavenging activity and α-amylase inhibitory activity (R (2) = 0.8967).