Antioxidant activity of taxifolin: an activity–structure relationship

Figures & data

Figure 1. Total antioxidant activity of taxifolin and standards like trolox, α-tocopherol, BHT, and BHA at the same concentration (30 μg/mL) assayed by the ferric thiocyanate method in the linoleic acid system. The control value reached a maximum 60 h (BHA, butylated hydroxyanisole; BHT, butylated hydroxytoluene).

Table 1. Determination of half maximal concentrations (IC₅₀) of taxifolin and standards belonging to Fe²⁺ chelating, DPPH√, ABTS√⁺, DMPD√⁺, and scavenging assays.

Antioxidants	Inhibition of lipid peroxidation (%)*	Fe^2+ chelating†	DPPH√ scavenging†	ABTS√^+ scavenging†	DMPD√^+ scavenging†	scavenging†
BHA	90.12	30.13	86.63	12.30	231.01	34.65
BHT	94.29	46.51	86.64	12.32	–‡	69.31
α-Tocopherol	73.88	19.81	13.86	01.01	–‡	93.01
Trolox	88.57	99.01	06.93	12.62	173.25	46.51
Taxifolin	81.02	34.61	77.00	0.83	231.04	09.91

*Percentage of lipid peroxidation inhibition on linoleic acid emulsion values determined after incubation period (60 h).

†Hydrophobic antioxidants such as α-tocopherol or BHT did not show activity in this assay.

‡They were determined as µg/mL.

Figure 2. Reducing power of taxifolin. (A) Fe³⁺→Fe²⁺ reductive potential of different concentrations (10–30 μg/mL) of taxifolin (r²: 0.960) and reference antioxidants. (B) Cu²⁺-reducing ability of different concentrations (10–30 μg/mL) of taxifolin (r²: 0.956) and reference antioxidants. (C) TPTZ-Fe³⁺→TPTZ-Fe²⁺ reductive potential of different concentrations (10–30 μg/mL) of taxifolin (r²: 0.993) and reference antioxidants (BHA, butylated hydroxyanisole; BHT, butylated hydroxytoluene).

Figure 3. Comparison of Fe²⁺-chelating activity of taxifolin (r²: 0.942) and standards like trolox, EDTA, α-tocopherol, BHT, and BHA at the concentrations of 10–20 mg/mL (BHA, butylated hydroxyanisole; BHT, butylated hydroxytoluene).

Figure 4. Possible places on taxifolin for chelating the transition metal ions such as Fe²⁺ in the process of lipid peroxidation.

Table 2. Determination of reducing power of taxifolin by K₃[Fe(CN)₆] reduction and FRAP methods, cupric ions (Cu²⁺) reduction capacity by Cuprac and FRAP methods*.

	Fe^3+–Fe^3+ reducing		Cu^2+–Cu^+ reducing		Fe^3+–TPTZ reducing
Antioxidants	IC50 (µg/mL)	R^2	IC50 (µg/mL)	R^2	IC50 (µg/mL)	R^2
BHA	3.006 ± 0.135	0.981	0.698 ± 0.49	0.951	2.811 ± 0.082	0.996
BHT	3.080 ± 0.168	0.979	0.717 ± 0.17	0.963	2.826 ± 0.140	0.987
α-Tocopherol	1.204 ± 0.145	0.967	0.525 ± 0.55	0.968	1.745 ± 0.108	0.983
Trolox	1.787 ± 0.102	0.969	0.618 ± 0.39	0.990	2.263 ± 0.114	0.994
Taxifolin	2.197 ± 0.108	0.960	0.750 ± 0.24	0.956	2.507 ± 0.136	0.993

*Expressed as absorbance values.

Figure 5. Radical-scavenging activity of taxifolin. (A) DPPH free radical-scavenging activity of different concentrations (10–30 μg/mL) of taxifolin (r²: 0.931) and reference antioxidants. (B) ABTS radical-scavenging activity of different concentrations (10–30 μg/mL) of taxifolin (r²: 0.925) and reference antioxidants. (C) DMPD radical-scavenging activity of different concentrations (10–30 μg/mL) of taxifolin (r²: 0.907) and reference antioxidants. (D) Superoxide anion radical-scavenging activity of different concentrations (10–30 μg/mL) of taxifolin (r²: 0.982) and reference antioxidants (BHA, butylated hydroxyanisole; BHT, butylated hydroxytoluene; DPPH√, 1,1-diphenyl-2-picryl-hydrazyl free radical; ABTS√⁺, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid; DMPD√⁺, N,N-dimethyl-p-phenylenediamine radical).

Figure 6. Stabilization of radicals by phenol group of taxifolin.

Figure 7. The proposed reaction scheme between DPPH free radicals and taxifolin.