Figures (4)  Tables (1)

    • Figure 1. 

      The chemical structure of the main purine alkaloids in tea plants.

    • Figure 2. 

      Purine alkaloids are synthesized from xanthosine which is produced via two main routes in tea and coffee: SAM route and AMP route (adapted from Ashihara et al.[16]).

    • Figure 3. 

      The main purine alkaloids biosynthesis pathway in tea plants (Adapted from Ashihara et al.[16]). (1) xanthosine 7-N-methyltransferase; (2) N-methylnucleosidase; (3) monomethylxanthine N-methyltransferase; (4) 3,7-dimethylxanthine N-methyltransferase TCS1; (5) 1,3,7-trimethyluric acid N-methyltransferase (CkTcS).

    • Figure 4. 

      The main purine alkaloids catabolic pathway in tea plants (Adapted from Ashihara et al.[16]).

    • Purine alkaloidsTeaCoffeeCacao
      ArabicaRobusta
      Caffeine2.0−5.01−1.52−2.71.5
      Theobromine0.06−1.0TraceTrace1.8
      Theacrine0.5−3.6 (rare)///
      Theophylline0.05TraceTraceTrace

      Table 1. 

      Purine alkaloids in tea, coffee and cacao (%).