Thermal activation in oxidative model drives catechin assembly into theaflavins with enhanced antioxidant capacity

Theaflavins are important bioactive pigments in tea, but their non-enzymatic formation pathways under heating remain incompletely understood. This study investigated the temperature-dependent formation of four theaflavins using aqueous catechin model systems. Potassium ferricyanide was used as a controlled oxidant to initiate catechin oxidation and subsequent coupling reactions. Liquid chromatography-mass spectrometry (LC-MS), ultraviolet-visible spectroscopy (UV–Vis), DPPH and ABTS assays were applied to track product profiles and antioxidant capacity. Moderate temperatures promoted catechin oxidation to ortho-quinones and favored the accumulation of theaflavins, leading to higher antioxidant activity. Low temperatures limited conversion, whereas high temperatures accelerated precursor consumption and theaflavin degradation. Across all model systems, theaflavin levels peaked at 30 min and then declined with prolonged heating. Among the four products, TF3 showed the strongest thermoresponsive and the highest antioxidant capacity. These findings reveal a thermally activated catechin self-assembly mechanism in an oxidant-assisted model system.