Journal of Tea Science Research, 2024, Vol.14, No.1, 57-63 http://hortherbpublisher.com/index.php/jtsr 58 by the human intestinal microbiota further underscores the complexity of tea's impact on health, with significant interindividual variability in metabolite profiles(Lee et al., 2006; Gross et al., 2010). The purpose of this review is to explore the intricate pathways of caffeine degradation during tea fermentation, mediated by diverse microbial communities. By examining the metabolic and metagenomic analyses of these microbial interactions, we aim to shed light on the potential improvements in tea quality and the associated health benefits. This review will delve into the current state of knowledge on the subject, identify gaps in the literature, and suggest directions for future research. 1 Caffeine Degradation by Fungi in Tea Fermentation 1.1Role of Aspergillus sydowii in caffeine degradation Aspergillus sydowii has been identified as a significant fungus in the solid-state fermentation (SSF) of Pu-erh tea, with a notable capacity to degrade caffeine. Research has shown that when A. sydowii is inoculated into sun-dried green tea leaves for SSF, it has a profound effect on the tea's chemical composition, including amino acids, carbohydrates, flavonoids, and particularly caffeine metabolism (Zhou et al., 2020a). Metabolomic analysis using UPLC-QTOF-MS and HPLC has revealed that A. sydowii can promote the production of various compounds, including ketoprofen, baclofen, and tolbutamide, as a result of caffeine degradation (Zhou et al., 2020a). The primary pathway for this degradation appears to be demethylation, leading to the production of significant amounts of theophylline and other demethylated xanthines (Zhou et al., 2020a). Remarkably, A. sydowii has been shown to convert approximately 93.24% of degraded caffeine into theophylline, producing 27.92 mg/g of theophylline after fermentation (Zhou et al., 2020a). This demonstrates the potential of using A. sydowii as a starter strain for the controlled and efficient biosynthesis of theophylline during tea fermentation (Zhou et al., 2020a). 1.2 Comparative analysis with other fungi The isolation and identification of caffeine-degrading microorganisms from Pu-erh tea have revealed a variety of fungi capable of degrading caffeine and its downstream metabolite, theophylline (Zhou et al., 2020b). Among these, Aspergillus niger and other Aspergillus species, such as Aspergillus ustus and Aspergillus tamarii, have been found to possess the ability to degrade theophylline in liquid culture (Zhou et al., 2020b). Comparative analysis of these fungi has shown that A. ustus and A. tamarii can degrade theophylline significantly, with A. ustus producing (129.48±5.81) mg/L of 3-methylxanthine and A. tamarii producing (159.11±10.8) mg/L of xanthine from theophylline in liquid medium (Zhou et al., 2020b). These findings suggest that different Aspergillus species have varying efficiencies in caffeine degradation and that they follow a similar N-demethylation pathway (Hakil et al., 1998; Zhou et al., 2020b). In terms of efficiency, A. sydowii has been highlighted as particularly effective in converting caffeine to theophylline during SSF of Pu-erh tea (Zhou et al., 2019; Zhou et al., 2020a). In contrast, A. niger, while also capable of degrading caffeine, has been shown to enhance caffeine content and not significantly influence theophylline content under certain conditions (Zhou et al., 2019). This suggests that while both A. sydowii and A. niger are involved in caffeine degradation, A. sydowii may be more efficient in producing theophylline as a specific demethylated product (Zhou et al., 2019; Zhou et al., 2020a). In conclusion, the role of Aspergillus sydowii in caffeine degradation during tea fermentation is significant, with the potential for practical applications in theophylline production. Comparative analysis with other fungi, such as Aspergillus niger, highlights the unique capabilities of A. sydowii and the importance of selecting appropriate starter strains for targeted metabolite production in fermented tea products (Zhou et al., 2019; Zhou et al., 2020a; Zhou et al., 2020b).
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