UV light-induced photodegradation of condensed tannins: obtaining bayberry tannins with different mean polymerization degrees

Abstract

Condensed tannins (CTs) characterized by a low degree of polymerization (DP) are recognized to have substantial value for applications across diverse industrial sectors, including food production, pharmaceuticals, and wood adhesive manufacturing. To acquire CTs with a low DP, the depolymerization of bayberry tannins (BTs) through a novel approach utilizing UV light-driven photocatalytic degradation, facilitated by the ultrasonic dispersion of TiO₂ nanoparticles was investigated. Under the optimal degradation conditions (a tannin concentration of 6%, a TiO₂ nanoparticles loading amount of 0.20%, and a degradation time of 4 h), the study delineated a discernible linear relationship correlating both the degradation time with the formaldehyde reactivity of the photocatalytic degradation products, and the formaldehyde reactivity with the mean degree of polymerization (mDP) of these photocatalytic degradation products. With the establishment of these correlative relationships, it is feasible to systematically control the degradation process of BTs. The photocatalytic degradation process adhered to the following mechanism: The degradation process of BTs is initiated by the cleavage of the C4-C8 bond which, at the incipient stage of degradation, results in the elimination of one gallocatechin gallate unit and one gallocatechin unit, or alternatively, the removal of a gallocatechin dimer. During the advanced stages of degradation, the opening of the C ring gives rise to different derivatives. Upon establishing optimal degradation parameters, it was observed that the primary constituents of the photocatalytic degradation products were dimers. The utilization of photocatalytic degradation exhibited an ability to break down condensed tannins in a manner that is both controllable and in an environmentally friendly way.