Flavonoids — quercetin, rutin, and morin — were kinetically studied as antioxidants in the scavenging of tert-butyl peroxyl radical ( \(tert - {\text{ butylOO}}^{ \bullet }\) ) and compared with the reference antioxidant Trolox. For the first time, a direct kinetic electron paramagnetic resonance (EPR) method with pulse injection of reagents was used to determine the anti \(tert - {\text{ butylOO}}^{ \bullet }\) capacity of the selected flavonoids. The antiradical capacities of the studied compounds were measured at − 32 °C and compared with the results obtained using the widely used oxygen radical absorbance capacity (ORAC) method. It was established that the kinetic EPR method with pulse reagent injection allows for effective and highly accurate determination of the anti-peroxyl radical capacities of polyphenolic compounds with multiple active centers, particularly flavonoids. The obtained data provide key insights for understanding structure–activity relationships (SAR) and the antiradical potential of flavonoids as peroxyl radical scavengers at the molecular level.
