Production of ellagic acid from degradation of valonea tannins by Aspergillus niger and Candida utilis

Abstract Two fungal strains, effective in converting valonea (Quercus aegilops) tannins into ellagic acid (EA), were isolated from soil contaminated by valonea tannins, and were tentatively identified as Aspergillus niger and Candida utilis. Properties of EA accumulation by the two isolates from valonea tannins' fermentation were studied. Both the strains preferred sucrose to glucose as the additional carbon and energy source. The most suitable concentrations of valonea tannins in fermentation media for EA accumulation by A niger and C utilis were 5.0 and 9.0 g dm−3 with EA yields of 12.1 and 8.9% (w/w), respectively. The optimal temperature for the two strains was 28 °C, while the preferred pH values of the fermentation media were 4.5–5.0 for A niger and 4.8–5.2 for C utilis. The tannin tolerances of A niger and C utilis were adapted to 20 and 25 g dm−3 by gradually increasing the concentrations of valonea tannins in the culture media. The adapted strain of A niger was able to completely degrade 20 g dm−3 valonea tannins with an EA yield of 14.3% in 9 days. Meanwhile, the adapted strain of C utilis decreased the valonea tannins' level from 25 to 9.1 g dm−3 with an EA yield of 11.48%. The degradation ability of A niger came from tannase whose activity in the medium was 63 U cm−3 at the ninth day of fermentation, and that of C utilis was due to both tannase and polyphenol oxidase (PPO) whose activities were 32 U cm−3 and 29 U cm−3 at the ninth day. The coculture of both the adapted strains could completely degrade 25 g dm−3 valonea tannins in only 7 days with a remarkably increased EA yield (21%). The activities of tannase and PPO of the coculture at the seventh day were 66 U cm−3 and 47 U cm−3 respectively, which proved the synergistic effect of the two enzymes on valonea tannins' degradation and EA accumulation. Copyright © 2005 Society of Chemical Industry