3-Methylxanthine production through biodegradation of theobromine by Aspergillus sydowii

Abstract

Background Methylxanthines including caffeine, theobromine and theophylline are natural and synthetic compounds in tea. Theobromine and other methylxanthine could be metabolized by certain kinds of bacteria and fungi. Previous studies confirmed that several isolates from Pu-erh tea could degrade and convert caffeine and theophylline through N-demethylation and related oxidation, respectively. In this study, seven tea-derived fungi were inoculated into various theobromine agar mediums and liquid mediums to assess their capacity in theobromine utilization. Related metabolites with theobromine degradation were detected by using HPLC in the liquid culture inoculated by candidate isolates to investigate potential application in the production of 3-methylxanthine. Results Based on the extent of theobromine utilization, four isolates including Aspergillus niger, Aspergillus sydowii, Aspergillus ustus and Aspergillus tamarii have demonstrated the potential for theobromine biodegradation. Particularly, A. sydowii and A. tamarii could degrade theobromine significantly (p < 0.05) in all given theobromine liquid mediums. 3,7-Dimethyluric acid, 3-methylxanthine, 7-methylxanthine, 3-methyluric acid, xanthine, and uric acid were detected in A. sydowii and A. tamarii culture, respectively, confirming the existence of N-demethylation and oxidation in theobromine catabolism. 3-Methylxanthine was common and main demethylated metabolite of theobromine in A. sydowii and A. tamarii culture. 3-Methylxanthine in A. sydowii culture showed a linear relation with the initial theobromine concentrations that 177.12 ± 14.06 mg/L of 3-methylxanthine was accumulated in TLM-S with 300 mg/L of theobromine. Additionally, pH at 5 and metal ion of Fe 2+ promoted 3-methylxanthine production significantly (p < 0.05). Conclusions This study is the first to confirm that A. sydowii and A. tamarii degrade theobromine through N-demethylation and oxidation, respectively. A. sydowii showed the potential application in 3-methylxanthine production with theobromine as feedstock through the N-demethylation at position N-7.