SPDS SET 2 METHODS - FOL-03

Journal of Agricultural and Food Chemistry

Article

Table 4. Comparison of the TEAC Coe ffi cients of the Tested Antioxidants Using Modi fi ed and Conventional Folin − Ciocalteu Methods with Those Found by Reference TAC Assays

Table 5. Theoretically Expected and Experimentally Found TAC Values (as mM Trolox-Equivalents) of Synthetic Mixtures Using the Modi fi ed Folin − Ciocalteu Method

synthetic mixture

TAC expected

TAC found

deviation (%)

original Folin − Ciocalteu method CUPRAC ABTS FRAP

modi fi ed Folin − Ciocalteu method

2.5 × 10 − 2 mM ascorbic acid 5.0 × 10 − 2 mM cysteine 1.4 × 10 − 1 mM vitamin E 2.5 × 10 − 2 mM quercetin 1.4 × 10 − 1 mM vitamin E 7.5 × 10 − 2 mM BHT 2.0 × 10 − 2 mM trolox 2.0 × 10 − 2 mM gallic acid 2.0 × 10 − 2 mM BHA 2.5 × 10 − 2 mM quercetin 2.5 × 10 − 3 mM rosmarinic acid 2.5 × 10 − 2 mM BHA 2.5 × 10 − 2 mM TBHQ 2.5 × 10 − 1 mM trolox 2.5 × 10 − 2 mM BHT 2.5 × 10 − 2 mM BHA 2.5 × 10 − 2 mM ca ff eic acid

− 7.08

0.127

0.118

antioxidants

− 3.78

0.185

0.178

trolox

1.00 2.78 1.78 1.88 2.61 3.23 0.39 0.82 0.99 1.90 1.30 1.60 0.34 4.08

1.00 1.80 2.54 5.59 5.54 10.6 2.04 2.92 3.16 1.38 4.54

1.00 5.77 3.25 1.47 2.89 3.10 1.02 0.77 1.57 1.02 1.68 1.03 1.75

1.00 1.00 3.98 2.92 4.17 1.85 1.70 0.87 1.39 1.13 2.40 1.24

quercetin gallic acid ferulic acid ca ff eic acid catechin vitamin E

0.285

0.290

+1.75

− 9.86

0.152

0.137

1.00 0.98 1.23 1.20 2.26

BHT BHA

TBHQ

− 5.08

0.295

0.280

LG

ascorbic acid β -carotene rosmarinic acid glutathione

0.99 1.01

0.72 10.5

2.14

− 7.14

0.196

0.182

5.2

2.5 × 10 − 2 mM quercetin 7.5 × 10 − 2 mM BHT

1.02 0.66

1.60 0.82

0.64 0.39

1.51 1.28

cysteine

Table 6. Theoretically Expected and Experimentally Found Absorbance ( A ) Values of Synthetic Mixtures of Lipophilic Antioxidants in Olive Oil Using the Modi fi ed Folin − Ciocalteu Method

with CUPRAC: TEAC CUPRAC

= 1.20 TEAC mod.Folin

+ 0.051 ( r =

0.802). Conventional FC with CUPRAC: TEAC CUPRAC

= 0.25

TEAC Folin TEAC ABTS

+ 1.24 ( r = 0.493). Modi fi ed FC with ABTS:

= 0.55 TEAC mod.Folin

+ 1.00 ( r = 0.466). Conven-

synthetic mixture

A expected

A found 0.912

deviation (%)

tional FC with ABTS: TEAC ABTS

= 0.05 TEAC Folin

+ 1.67 ( r =

3.75 × 10 − 2 mM BHT 1.25 × 10 − 2 mM TBHQ 6.00 × 10 − 2 mM trolox olive oil 2.50 × 10 − 2 mM BHA 3.75 × 10 − 2 mM BHT 1.25 × 10 − 2 mM TBHQ olive oil 2.50 × 10 − 2 mM vitamin E 1.25 × 10 − 2 mM TBHQ 1.88 × 10 − 2 mM BHA olive oil

− 3.83

0.948

0.134). TAC Determination of Synthetic Mixtures of Anti- oxidants. Ternary and quaternary synthetic mixtures of hydrophilic and lipophilic antioxidants (the latter with or without olive oil as a complex sample medium) were analyzed with the modi fi ed Folin − Ciocalteu method, and the observed overall TAC values were found to approximate the sum of the individual TAC values of constituents. The results for the theoretically expected and experimentally found TAC values were in agreement within 10%, as shown in Table 5. In addition, the theoretically expected and experimentally found absorbance values of ternary synthetic mixtures of antioxidants in olive oil sample agreed within ± 5% (Table 6). Additivity and Interference E ff ects in TAC Determi- nation. Additivity of antioxidant capacities of individual antioxidants in a mixture is important in de fi ning TAC, and the additivity property of antioxidant capacities can be demonstrated either in synthetic antioxidant mixtures (as in Tables 5 and 6) or in the standard addition of a selected antioxidant to a complex mixture. When applying the standard addition method, the calibration curves of a chosen antioxidant fi rst in standard reaction medium and second in another antioxidant solution or complex matrix such as olive oil/sage/ green tea extract were drawn (Figures 6 − 8). Figures 6 − 8 indicate the parallelism of the mentioned pair (i.e., the slopes agreed within ± 10%) of curves and consequently the lack of interference (in the form of association, dissociation, or interaction with solvent molecules) in the modi fi ed FC assay in agreement with Beer ’ s law. The potential interferents common in food plants and botanicals such as citric acid, glucose, mannitol, serine, lysine, valine, proline, and alanine did not signi fi cantly a ff ect the

0.840

0.868

+3.22

− 2.57

0.745

0.725

Figure 6. Calibration line of BHT (the regression equations: ◆ , y = 4.55 × 10 3 x + 0.0068, R 2 = 0.9830, in pure reaction medium, ■ , y = 4.50 × 10 3 x + 0.1436, R 2 = 0.9926, in BHA solution) with respect to the modi fi ed Folin − Ciocalteu method.

4788

dx.doi.org/10.1021/jf400249k | J. Agric. Food Chem. 2013, 61, 4783 − 4791