3.5. The Oxygen Radical Antioxidant Capacity (ORAC)

ORAC employs a competitive reaction scheme between antioxidants and a fluorescence probe for a peroxyl radical [63]. As the fluorescent probes, fluorescein or 2′,7′-dichlorofluorescein diacetate are most often used. This assay allows to accurately measure both the inhibition time and the inhibition degree of lipophilic and hydrophilic antioxidants to ensure an accurate measurement of the antioxidant activity. The time of analysis is long as it measures the reaction until its completion and detects fast- and slow-reacting antioxidants. ORAC values were only reported for p-CA and CFA [117], and expressed as Trolox equivalents (Table 3). In both studies, CFA had higher ORAC values than p-CA and thus higher antioxidant activity. Villaño et al. [62] demonstrated that BA derivatives showed lower antioxidant activity compared to CinA derivatives. They observed the effect of the catechol group on the activity towards peroxyl radicals of both BA and CinA derivatives. Indeed, the highest ORAC values were reported for compounds containing a catechol group in their structure.