Abstract: Nucleotide is a kind of important substrate for the biosynthesis of nucleic acid and caffeine in tea, which is also one of the most important umami substances in tea infusion. Ultra-high performance liquid chromatography-quadrupole/electrostatic field orbitrap high-resolution mass spectrometry was used for the determination of nucleotide contents. Five types of flavored nucleotides including cytidine 5'-monophosphate (CMP), uridine 5'-monophosphate (UMP), adenosine 5'-monophosphate (AMP), inosine 5'-monophosphate (IMP) and guanosine 5'-monophosphate (GMP) in tea were determined within 4 min, and dynamic changes of the above nucleotide contents in the making green process of ‘Tieguanyin’ Oolong tea were analyzed. The results show that the detection limits of the five nucleotides were 0.87-1.47 μg·g^-1, with the limits of quantification of 2.62-4.41 μg·g^-1 and a linear range of 50-1 000 ng·mL^-1. The intra-day and inter-day precisions were 2.17%-4.17% and 2.95%-4.74%, with a recovery rate of 72.89%-91.98%. Three types of nucleotides, AMP, CMP and UMP, were detected in tea cultivar ‘Tieguanyin’, with the UMP content of 16.98-26.78 μg·g^-1, the CMP content of 14.31-17.56 μg·g^-1, and the AMP content of 7.80-9.91 μg·g^-1. The UMP, CMP, and AMP in ‘Tieguanyin’ were ranked in order from high to low and the CMP content increased slowly in late stages of making green process. The total amount of flavored nucleotides in the making green process varied from 40.78 to 56.69 μg·g^-1, showing the trend of mild and stable fluctuation. The method is rapid, accurate and sensitive with high stability and precision, which can be used as an analytical technique for the study of flavor chemistry in tea processing.

Key words: Tieguanyin, umami taste, making green, flavored nucleotide