Component and Structure of Aspergillus flavipes sp.-Biodegraded Bayberry Tannins: A Potential Routine for Condensed Tannin Cleaner Degradation and Disposal

Abstract

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.

Effects of Fermentation on Bioactivity and the Composition of Polyphenols Contained in Polyphenol-Rich Foods: A Review

“…Hydrolysable tannins are composed of glycosidic and lipid bonds. Condensed tannins, also known as proanthocyanidins, are complex polymers with flavan-3-ol as the base structure [110]. As shown in Figure 2A, Ascacio et al [111] studied the degradation process of prune tannin and found that prune tannin belonged to a polymer of ellagic acid (ellagitannin), in which, under the action of tannase secreted by Aspergillus niger, the lipid bond was broken to form punicalin, and under the action of β-glucosidase, the glycosidic bond was cleaved from polysaccharides to form gallagic acid, and finally an ellagic acid monomer was formed.…”