Journal of Tea Science Research, 2024, Vol.14, No.1, 57-63 http://hortherbpublisher.com/index.php/jtsr 59 2 Caffeine Degradation Pathways 2.1 Demethylation as a primary pathway The demethylation process is a critical pathway in the degradation of caffeine, particularly by the fungus Aspergillus sydowii during tea fermentation. Studies have shown that A. sydowii can significantly influence the metabolic profile of Pu-erh tea during solid-state fermentation (SSF), impacting not only caffeine but also amino acids, carbohydrates, and flavonoids. The utilization of UPLC-QTOF-MS and HPLC methods has revealed that A. sydowii facilitates the degradation of caffeine into demethylated metabolites such as theophylline and 3-methylxanthine. Remarkably, a substantial portion of the degraded caffeine, approximately 93.24%, is converted into theophylline, with a production of 27.92 mg/g after fermentation (Zhou et al., 2020a). Another study corroborates these findings, indicating that A. sydowii NRRL250 is capable of completely degrading caffeine in a liquid medium and significantly increasing the levels of theophylline and 3-methylxanthine as the primary degradation products (Zhou et al., 2018a). 2.2 Alternative degradation pathways Exploration of caffeine degradation by various food microorganisms has revealed alternative pathways. A study focusing on the degradation of caffeine by Lactobacillus casei, Leuconostoc mesenteroides, Rhizopus oryzae, and Saccharomyces cerevisiae has demonstrated that these microorganisms can transform caffeine into dimethylxanthine and subsequently into methylxanthine. Notably, more than 89% of caffeine is converted into paraxanthine, which is then further transformed into either 1-methylxanthine by L. casei and L. mesenteroides or 7-methylxanthine by R. oryzae and S. cerevisiae. This indicates the presence of two distinct degradation patterns: the caffeine-paraxanthine-1-methylxanthine pathway and the caffeine-paraxanthine-7-methylxanthine pathway, with the former being utilized by L. casei and L. mesenteroides and the latter by R. oryzae and S. cerevisiae (Purwoko et al., 2023). In summary, the primary pathway for caffeine degradation in A. sydowii involves demethylation, leading to the production of theophylline and 3-methylxanthine. However, alternative pathways exist in other food microorganisms, resulting in different patterns of degradation and metabolites. These findings are crucial for understanding the metabolic processes during tea fermentation and could have practical applications in controlling caffeine content and enhancing the production of specific metabolites in fermented tea products. 3 Optimization of Caffeine Degradation Conditions 3.1 Analysis of optimal conditions for caffeine degradation by Aspergillus sydowii The degradation of caffeine by Aspergillus sydowii has been a subject of interest due to its potential application in the production of decaffeinated tea products. Research has identified Aspergillus sydowii NRRL250 as an effective strain for caffeine degradation in Pu-erh tea fermentation (Zhou et al., 2018a; Zhou et al., 2018b). The optimal conditions for caffeine degradation by this strain were determined through single-factor analysis, which revealed that a substrate concentration of 1,200 mg/L, a reaction temperature of 30 °C, and a pH of 6 were ideal for the process (Zhou et al., 2018a). Under these conditions, A. sydowii NRRL250 was capable of completely degrading 600 mg/L of caffeine in a liquid medium, and when applied to submerged fermentation of tea infusion, it degraded 985.1 mg/L of caffeine, producing 501.2 mg/L of theophylline (Zhou et al., 2018a). 3.2 Influence of substrate concentration, reaction temperature, and pH on degradation efficiency The efficiency of caffeine degradation by A. sydowii is significantly influenced by substrate concentration, reaction temperature, and pH. A study demonstrated that varying the initial caffeine concentrations (600, 1,200, and 1,800 mg/L) affected the degradation products, with theophylline and 3-methylxanthine being the main products detected (Zhou et al., 2018b). The concentration of caffeine had a significant impact on the production of these degradation products, indicating that higher substrate concentrations could enhance the production of theophylline and 3-methylxanthine (Zhou et al., 2018b).
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