Degradation of procyanidins by Aspergillus fumigatus: identification of a novel aromatic ring cleavage product

Abstract

Aspergillus fumigatus was able to grow on apple-purified procyanidins (PCs). PCs concentration decreased 30% over the first 60 h of liquid fermentation. The mean degree of polymerization (DPn) of apple-purified PCs increased from 8 to 15 during the fermentation. A fungal enzyme extract from the liquid fermentation was used to study procyanidin B2 [(-)-epicatechin-(4beta-8)-(-)-epicatechin] degradation. The major degradation product (PB2-X) had a retention time of 10.5 min and a molecular mass at m/z 609. High-performance liquid chromatography/multiple fragment mass spectrometry (HPLC/MS(n)) was used for the structural characterization of PB2-X as well as that of thiolysis-treated PB2-X. Twelve fragment ions at m/z 565, 547, 457, 439 (two fragment ions), 421, 413, 377, 395, 351, 287 and 277 were completely identified. It was therefore deduced that the terminal unit of procyanidin B2 dimer was modified by an oxygenase from A. fumigatus leaving the extension unit intact. In addition, FT-IR analysis confirmed a lactone formation in (-)-epicatechin moiety involved in oxidative degradation. Two reaction schemes were postulated for the interpretation of the results.