Assessing the activity of natural food antioxidants - Oxidation in Foods and Beverages and Antioxidant Applications - page 346

Table 14.4 Antioxidant activity of selected AHs using DPPH · and ABTS · assays by
the same analyst

DPPH · Order of ABTS · AHs Order of Reference

(%RSA)* activity (TEAC) activity

within within

groups groups

Hydroxycinnamic acid
Rosmarinic acid 88.4 1 2.13 1 115, 122

Caffeic acid 76.6 2 1.01 5

Chlorogenic acid 52.0 4 0.95 6

Sinapic acid 56.1 3 1.27 4

Ferulic acid 30.9 5 1.32 3

p-Coumaric acid 3.6 6 2.00 2

Simple phenols
Catechol 65.1 1 0.97 2 122

Resorcinol 2.7 3 1.14 1

Hydroquinone 48.6 2 0.68 3

Benzoic acids
Gallic acid 96.3 1 2.18 1 122

Protocatechuic acid 68.7 2 0.84 2

Resorcilic acid 2.9 3 0.63 3

Flavonoids
Quercetin 68.2 1 1.85 1 122

Morin 43.2 2 1.20 2

* Values obtained at the ratio [AH]/[DPPH · ] 0.25; t 20 min

The models usually employed in lipid oxidation studies are bulk oils and
dispersed systems (e.g., micelles, emulsions, liposomes). Other more complex
matrices are less frequently met. Variability in the type of the substrates found in
the literature is remarkable. It seems that choices for substrates are influenced by
prevailing views.

14.7.1 Bulk oils
The oxidation of bulk oils is a common approach to test the efficacy of
antioxidants. The lipid substrate (e.g., free fatty acid, fatty acid methyl ester,
mixtures of triacylglycerols), which has been stripped of pro-/anti-oxidant
factors, 123 is often oxidized under accelerated conditions in the absence or the
presence of AHs at various concentrations. The accumulation of primary and
secondary oxidation products is followed periodically.
Oxidation of bulk oils is usually carried out through stability tests, such as the
Schaal oven test (40±60 ëC), the Active Oxygen Method (AOM) (100 ëC,
purging air through the sample), or the Rancimat apparatus (T > 100 ëC,
purging air through the sample). The two latter procedures have been criticized