Comparison of the degradation kinetics of A-type and B-type proanthocyanidins dimers as a function of pH and temperature

The degradation behaviors of four different proanthocyanidins dimers including B-type (e)picatechin (E)C dimer and A-type (epi)catechin (E)C dimer, A-type (epi)catechin-3-O-gallate (E)CG dimer and A-type (epi)gallocatechin-3-O-gallate (E)GCG dimer as affected by pH and temperature were compared in this study. The results showed that the stability of proanthocyanidins dimers was not only temperature and pH dependent, but also structure dependent. Proanthocyanidins dimers were found to be unstable at pH as low as 1.5 and physiological pH conditions, and they were rather unstable at alkaline conditions and temperature above 25 °C. Among the four dimers tested, B-type (E)C dimer was the least stable, while A-type (E)C dimer was the most stable. In general, B-type dimers showed less stability than A-type ones. The higher the degree of galloylation and the more the hydroxyl groups in the molecular, the less stable the proanthocyanidins dimers.