Photo-catalytic polymerization of catechin molecules in alkaline aqueous

- Catechin molecule is sensitive to visible blue light in alkaline aqueous.
- Blue light irradiation catalyzes the polymerization of catechins.
- Photocatalytic polymerization of catechins forms B-type proanthocyanidin.
- The dimeric catechin has a promoted antioxidant activity in vitro.

Polyphenols are associated with a wide range of physiological properties. Catechin is a flavan-3-ol with five phenolic hydroxyl groups. After blue light illumination, the transparent solution of catechin became yellowish. The effects of visible light illumination (400-800 nm) were investigated on molecular structures and antioxidant capacities of catechin. Under the neutral or alkaline aqueous with the illumination of blue light, the photolysis and polymerization of catechin were observed in this study. A chromogenic catechin dimer was separated and identified as a proanthocyanidin by the chromatographic technique and mass spectrometry. For quantitative evaluation, the signal intensities of the catechin and the photochemical product show a negative correlation in the liquid chromatograms. The oligomer of flavan-3-ols (catechin dimer) is suggested as a dimeric B type proanthocyanidin, which has the molecular formula C30H26O12 and 578.14 g/mol in exact mass. The mass spectrum of catechin dimer had characteristic ion signals in m/z 577, 560, 439 Da. However, the total phenolic contents and scavenging O2− activity of catechin treated by blue light illumination are not changed significantly at the neutral or alkaline aqueous. Our results of photocatalytic oligomers of catechin provide a novel way to explain the sensory changes of green tea and a biochemical mechanism under the irradiation environments.

Graphical Abstract