Abstract: To identify fungi strain involved in caffeine degradation in Pu-erh tea, caffeine liquid medium was used to screen target strain in Pu-erh tea of different stages during solid-state fermentation. The candidate strains were then analyzed for colony morphology, morphological characteristics and 18βS rDNA. The target strain was inoculated into tea for fermentation. Caffeine, theophylline, theobromine and 3-methylxanthine were determined by HPLC during the fermentation process. Results showed that the most effective strain was isolated from Pu-erh tea during solid-state fermentation, which could degrade 87.70% caffeine within 48 hours and was identified as Aspergillus sydowii with similarity of 99.8%. During the inoculated fermentation with Aspergillus sydowii, caffeine declined sharply and only 0.414%±0.077% (w/w) was reserved. Theophylline increased significantly from less than 0.1% (w/w) to 2.129% ±0.246% (w/w) and became the major purine alkaloid. Theobromine was relatively stable without significant change (P<0.05). The 3-Methylxanthine content had an obvious increase by 130%. The fungi stain was firstly isolated and identified to be involved in caffeine degradation, which confirmed fungus will facilitate the production of decaffeinated Pu-erh tea. In addition, caffeine biotransformation products were developed.

Key words: Aspergillus sydowii, caffeine, theophylline, Pu-erh tea, solid-state fermentation