Mapping antioxidant mechanisms in plant extracts via reactivity kinetics inhibiting oil autoxidation

• Kinetic data revealed mechanisms of antioxidant action in complex plant extracts. • Lamiaceae extracts showed strongest inhibition due to high rosmarinic acid. • Rosmarinic acid showed highest peroxyl-radical scavenging reactivity. • Kinetics‐driven insights update sustainable food preservation strategies. This study aims to investigate the reactivity kinetics of natural antioxidants in plant extracts from three families ( Asteraceae, Lamiaceae , and Rosaceae ) in inhibiting sunflower oil autoxidation. Extracts obtained via ultrasound-assisted extraction were added to stripped sunflower oil (SSO; natural antioxidants removed) and autoxidation kinetics were monitored using isothermal calorimetry at 30 °C. Of the 15 tested extracts, 11 efficiently inhibited SSO autoxidation, with inhibition rate constants ( k inh ) on the order of 10 4 M -1 s -1 . Satureja montana and Tagetes erecta exhibited the highest k inh values. To better understand antioxidant mechanisms, extracts were characterized for their phytochemical composition, and the major phenolic compounds identified were tested individually. Rosmarinic acid showed the highest k inh value, followed by quercetin ≈ caffeic acid > catechin > chlorogenic acid > ellagic acid > luteolin. The k inh values of the whole extracts were lower than those of the most reactive individual compounds, suggesting competitive interactions among constituents with varying reactivities that diminish overall antioxidant performance. Lamiaceae species, rich in rosmarinic acid, were particularly effective at scavenging peroxyl radicals and demonstrated strong potential as natural alternatives to synthetic antioxidant, BHT. By linking phytochemical composition with kinetic behavior, this study offers mechanistic insights into how antioxidants function in complex systems. The findings support the use of plant-based antioxidants in food preservation and propose a robust, kinetics-based approach for evaluating antioxidant performance in complex mixtures.