SPDS SET 2 METHODS - FOL-03

Journal of Agricultural and Food Chemistry

Article

Table 1. Analytical Figures of Merit Found by the Conventional Folin − Ciocalteu Method for Samples Containing both Hydrophilic and Lipophilic Antioxidants

regression coe ffi cient ( N = 3)

molar absorption coe ffi cient (L mol − 1 cm − 1 )

antioxidants

linear calibration equation

linear concn range (M) TEAC

A = − 7.70 × 10 − 3 + 2.02 × 10 3 C TR A = − 0.80 × 10 − 2 + 3.64 × 10 3 C QR A = − 4.92 × 10 − 1 + 5.14 × 10 3 C GA A = 1.00 × 10 − 1 + 1.13 × 10 4 C FA A = − 1.80 × 10 − 2 + 1.12 × 10 4 C CA A = − 1.24 × 10 − 1 + 2.15 × 10 4 C CAT A = − 1.00 × 10 − 2 + 4.12 × 10 3 C VITE A = 5.93 × 10 − 2 + 5.89 × 10 3 C BHT A = 6.24 × 10 − 2 + 6.38 × 10 3 C BHA A = − 4.09 × 10 − 2 + 2.79 × 10 3 C TBHQ A = − 1.57 × 10 − 2 + 9.18 × 10 3 C LG A = 2.20 × 10 − 3 + 1.47 × 10 3 C CAR A = − 7.40 × 10 − 3 + 2.13 × 10 4 C RA A = − 7.06 × 10 − 2 + 1.22 × 10 3 C GSH A = − 1.68 × 10 − 1 + 1.65 × 10 3 C CYS A = 5.77 × 10 − 2 + 5.51 × 10 3 C TR A = 1.06 × 10 − 1 +1.53 × 10 4 C QR A = 9.86 × 10 − 2 + 9.82 × 10 3 C GA A = 4.65 × 10 − 2 + 1.04 × 10 4 C FA A = 3.97 × 10 − 2 + 1.44 × 10 4 C CF A = 1.96 × 10 − 2 +1.78 × 10 4 C CAT A = 6.35 × 10 − 2 + 2.15 × 10 3 C TOC A = 3.14 × 10 − 2 + 4.50 × 10 3 C BHT A = 5.13 × 10 − 2 + 5.45 × 10 3 C BHA A = 2.98 × 10 − 2 + 1.05 × 10 4 C TBHQ A = 7.59 × 10 − 2 + 7.17 × 10 3 C LG A = 2.53 × 10 − 2 + 8.79 × 10 3 C ASC A = 3.85 × 10 − 2 + 1.87 × 10 3 C CAR A = 6.81 × 10 − 2 + 2.25 × 10 4 C RA A = 1.07 × 10 − 1 + 5.65 × 10 3 C GSH A = 5.56 × 10 − 2 + 3.63 × 10 3 C cys linear calibration equation

2.1 × 10 − 5 − 1.7 × 10 − 4 2.1 × 10 − 6 − 2.5 × 10 − 5 8.4 × 10 − 5 − 3.4 × 10 − 4 1.0 × 10 − 5 − 8.4 × 10 − 5 1.1 × 10 − 5 − 8.7 × 10 − 5 1.1 × 10 − 5 − 5.4 × 10 − 5 4.0 × 10 − 5 − 1.5 × 10 − 4 4.2 × 10 − 5 − 1.7 × 10 − 4 4.2 × 10 − 5 − 1.5 × 10 − 4 6.3 × 10 − 5 − 5.0 × 10 − 4 2.1 × 10 − 5 − 1.0 × 10 − 4 4.2 × 10 − 5 − 2.1 × 10 − 4 5.3 × 10 − 6 − 5.3 × 10 − 5 1.2 × 10 − 4 − 1.2 × 10 − 3 1.0 × 10 − 4 − 8.4 × 10 − 4 linear concn range (M) 2.00 × 10 − 4 − 1.00 × 10 − 3 2.00 × 10 − 5 − 1.00 × 10 − 4 4.00 × 10 − 5 − 2.00 × 10 − 4 1.00 × 10 − 5 − 8.00 × 10 − 5 1.00 × 10 − 5 − 8.00 × 10 − 5 5.00 × 10 − 6 − 6.00 × 10 − 5 2.80 × 10 − 5 − 2.80 × 10 − 4 2.00 × 10 − 5 − 1.60 × 10 − 4 2.00 × 10 − 5 − 1.00 × 10 − 4 5.00 × 10 − 6 − 6.00 × 10 − 5 2.00 × 10 − 5 − 8.00 × 10 − 5 2.00 × 10 − 5 − 1.00 × 10 − 4 4.00 × 10 − 5 − 2.00 × 10 − 4 5.00 × 10 − 6 − 6.00 × 10 − 5 2.00 × 10 − 5 − 1.00 × 10 − 4 4.00 × 10 − 5 − 2.00 × 10 − 4

2.02 × 10 3 3.64 × 10 3 5.14 × 10 3 1.13 × 10 4 1.12 × 10 4 2.15 × 10 4 4.12 × 10 3 5.89 × 10 3 6.38 × 10 3 2.79 × 10 3 9.18 × 10 3 1.47 × 10 3 2.13 × 10 4 1.22 × 10 3 1.65 × 10 3

0.9829 0.9858 0.9485 0.9972 0.9985 0.9742 0.9963 0.9270 0.9973 0.9672 0.9840

1.00 1.80 2.54 5.59 5.54 10.6 2.04 2.92 3.16 1.38 4.54

trolox

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

BHT BHA

TBHQ

LG

ascorbic acid β -carotene rosmarinic acid glutathione

0.9952 0.9922

0.72 10.5

0.9981 0.9876

0.60 0.82

cysteine

Table 2. Analytical Figures of Merit Found by the Modi fi ed Folin − Ciocalteu Method for Samples Containing both Hydrophilic and Lipophilic Antioxidants

regression coe ffi cient ( N = 3)

molar absorption coe ffi cient (L mol − 1 cm − 1 )

LOD (M) ( N = 8) 0.91 × 10 − 6 0.33 × 10 − 6 0.51 × 10 − 6 0.48 × 10 − 6 0.35 × 10 − 6 0.28 × 10 − 6 2.33 × 10 − 6 1.11 × 10 − 6 0.92 × 10 − 6 0.48 × 10 − 6 0.69 × 10 − 6 0.56 × 10 − 6 2.68 × 10 − 6 2.23 × 10 − 6 0.89 × 10 − 6 1.38 × 10 − 6

LOQ (M) ( N = 8) 3.00 × 10 − 6 1.91 × 10 − 6 1.70 × 10 − 6 1.61 × 10 − 6 1.16 × 10 − 6 0.94 × 10 − 6 7.76 × 10 − 6 3.71 × 10 − 6 3.06 × 10 − 6 1.59 × 10 − 6 2.32 × 10 − 6 1.89 × 10 − 6 8.93 × 10 − 6 7.42 × 10 − 6 2.96 × 10 − 6 4.60 × 10 − 6

antioxidants

TEAC

5.51 × 10 3 1.53 × 10 4 9.82 × 10 3 1.04 × 10 4 1.44 × 10 4 1.78 × 10 4 2.15 × 10 3 4.50 × 10 3 5.45 × 10 3 1.05 × 10 4 7.17 × 10 3 8.79 × 10 3 1.87 × 10 3 2.25 × 10 4 5.65 × 10 3 3.63 × 10 3

0.9961 0.9981 0.9905 0.9998 0.9971 0.9940 0.9884 0.9980 0.9977 0.9929 0.9881 0.9975 0.9874 0.9943

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

trolox

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

BHT BHA

TBHQ

LG

ascorbic acid β -carotene rosmarinic acid glutathione

0.9417 0.9931

1.02 0.66

cysteine

values in Table 1. As a distinct advantage over the conventional FC method, ascorbic acid can be reliably assayed by the proposed FC modi fi cation (Table 2). Since the molar absorptivity for trolox showed more than a 2-fold increase with the modi fi ed method, the TEAC coe ffi cients for most antioxidants dropped to normal levels, as found by other standard tests (Table 4). Thus, the extremely high TEAC values for rosmarinic acid and catechin, which may originate from the high oxidizing power of the conventional FC reagent, 5,22 were brought to acceptable levels using the proposed method, generally in accordance with the results of standard CUPRAC, ABTS, and FRAP assays (Table 4). The correlation equations calculated with the aid of TEAC coe ffi cients given in Table 4 are presented below. According to these results, there is a signi fi cant correlation (at 95% con fi dence level) between the CUPRAC and modi fi ed FC methods. However, the conventional FC method did not show an acceptable correlation with the other methods. Modi fi ed FC

green tea infusion (Table 3). The TEAC coe ffi cient is de fi ned as the ratio of the slope of the calibration curve of the tested

Table 3. Analytical Figures of Merit Found in Complex Food Matrices by the Modi fi ed Folin − Ciocalteu Method ( N = 5)

3.0 × 10 − 5 M vitamin E added to olive oil sample

6.0 × 10 − 5 M trolox added to green tea infusion

validation parameters

1.51 × 10 − 5 5.05 × 10 − 5

5.77 × 10 − 6 1.92 × 10 − 5

LOD (M) LOQ (M)

recovery (%)

103.1

103.3

RSD (%)

7.46

4.04

antioxidant to that of trolox for each assay. The most characteristic feature of the modi fi ed FC assay is the signi fi cantly improved linear correlation coe ffi cients for phenolics (Table 2), especially for synthetic antioxidants (BHT, BHA, TBHQ, and LG), compared to the corresponding

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