Component and Structure of Aspergillus flavipes sp.-Biodegraded Bayberry Tannins: A Potential Routine for Condensed Tannin Cleaner Degradation and Disposal
ACS Omega. 2022 Feb 9;7(7):5809-5816. doi: 10.1021/acsomega.1c05768. eCollection 2022 Feb 22.
Chemical degradation is widely used for producing lower-molecular-weight tannin compounds and tannin disposal, but it has negative effects on the environment, such as causing secondary pollution and consuming energy. For overcoming these disadvantages, a cleaner and sustainable degradation and disposal method for condensed tannins was developed through biodegradation. In this study, bayberry tannin solution, one kind of condensed tannin, was biodegraded by Aspergillus flavipes sp. at first; then, gel permeation chromatography and high-performance liquid chromatography were used for separating the biodegraded and original tannins to analyze the differences in components; finally, the changes in the tannin structure after biodegradation were characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and nuclear magnetic resonance. The results showed that the high-molecular-weight components decreased while the low-molecular-weight components increased when bayberry was subjected to A. flavipes sp. biodegradation; furthermore, the molecular weight of the biodegraded bayberry tannin decreased from 3371 to 2658 Da. Meanwhile, the structure of bayberry tannin polyflavonoids, especially A ring and C ring together with the galloyl group, was destroyed and some small fragments were generated during biodegradation. These structural changes resulted in the increase of low-molecular-weight phenols but the decrease of polyflavonoids after bayberry biodegradation. These would be the pieces of evidence showing that A. flavipes sp. consumed simple phenols as nourishment for growth and converted polyflavonoids into low-molecular-weight substances at the same time. To sum up, biodegradation can be used in every field where condensed tannins should be degraded or removed for a cleaner and ecofriendly routine.