Assessing the activity of natural food antioxidants - Oxidation in Foods and Beverages and Antioxidant Applications - page 340

intensity in non-polar organic solvents is rather low. For this reason the use of a
suitable alternative is the pair of the fluorescent fatty acid 4,4-difluoro-3,5-bis(4-
phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene known as BODIPY 665/676
and 2,2 0 -azobis-2,4-dimethylvaleronitrile (AMVN) as a lipid peroxyl radical
generator. 69 The method is of increasing popularity among researchers and has
been proposed for standardization by Prior et al., during the first international
congress on antioxidant methods. 30 The merits of this protocol are:
· applicability to both hydrophilic and lipophilic antioxidants,
· automation potential (multichannel liquid handling system) that assist

parallel analysis of numerous samples (high-throughput), 67,70,71
· good linearity of AUC vs antioxidant concentration, 70
· good precision (CV% < 3.0). 71

Though the extended use of ORAC for testing food extracts and beverages,
its application to the assessment of individual compounds activity is rather
limited. 3,71±75 It should be stressed that under ORAC assay conditions gallic
acid, which is known to be a very efficient antioxidant, is estimated to be of low
potency, 3,71 while compounds such as tyrosine and tryptophan that are not
strong antioxidants were found to be very efficient and presented high ORAC
values. 76

Activity order of phenolic compounds based on the parallel use of CBA and
ORAC data
Data on the activity of AHs can be found in the literature regarding the use of
either CBA or ORAC assay. Those presented by Ordoudi et al., 5,73 (Table 14.3)
indicated both similarities (e.g., quercetin) or deviations (e.g., protocatechuic/
homoprotocatechuic acids) in the order of activity. On physical organic
chemistry grounds, ORAC values based order deviated more than expected.

Table 14.3 Antioxidant activity of selected AHs using CBA and ORAC assay by the
same analyst

AH CBA Order of ORAC Order of Reference

activity activity

TEV krel * TEV*

(n 3) (n 3)

Protocatechuic acid 0.71 4 1.51 8 5

o-Pyrocatechuic acid 0.18 8 2.84 7

Homoprotocatechuic acid 0.54 7 4.48 4 73,

Dihydrocaffeic acid 0.63 5 3.34 6 Ordoudi and Tsimidou

Caffeic acid 3.51 3 5.20 2 (unpublished)

Catechol 0.53 6 3.76 5

Rosmarinic acid 4.53 2 4.68 3 5

Quercetin 5.03 1 6.50 1

* Data given as Trolox equivalent values (TEV)