Polymerization of proanthocyanidins catalyzed by polyphenol oxidase from lotus seedpod

This study aimed to investigate the profiles change in proanthocyanidins (PAs) catalyzed by polyphenol oxidase (PPO) from lotus seedpod in a model wine system (MWS). Results showed that PAs from lotus seedpod consisted of dimer (74.00 %) and trimer (22.75 %). PPO could tolerate ethanol concentrations below 20 % (v/v). The optimum temperature of PPO activity was 80 °C, and the optimal pH was 9.0. Its molecular weight was approximately 31 kDa, and its secondary structures were α-helix (59.0 %), β-sheet (4.3 %), turns (14.1 %), and random coils (22.6 %). In the MWS, the trimers gradually increased from 22.55 % at 0 h (control) to 100 % at 10 h incubation, while the dimers decreased from 74.33 % (control) to 0 % at 10 h incubation. Moreover, the composition of the precipitate formed at different incubation time points was approximately 16.54 % of monomers, 21.03 % of dimers, and 62.43 % of trimers at 2 h incubation with PPO. The results from this study have provided in vitro evidence for a possible application of PPO in red wine aging.