UHPLC-Q-Orbitrap HRMS测定乌龙茶中呈味核苷酸及铁观音做青过程中呈味核苷酸变化分析

Determination of Flavored Nucleotides in Oolong Tea by Ultra-High Performance Liquid Chromatography-Quadrupole/Orbitrap High Resolution Mass Spectrometry and Changes of Flavored Nucleotides in the Making Green Process of‘Tieguanyin’Tea

核苷酸是茶叶中核酸和咖啡碱生物合成的重要底物,也是茶汤中重要的鲜味物质之一。建立了一种超高效液相色谱-四极杆/静电场轨道阱高分辨质谱法(UHPLC-Q-Orbitrap HRMS)测定核苷酸含量的分析方法,可在4 min内测定茶叶中胞苷-5’-单磷酸(CMP)、尿苷-5’-单磷酸(UMP)、腺苷-5’-单磷酸(AMP)、肌苷-5’-单磷酸(IMP)和鸟苷-5’-单磷酸(GMP)等5种呈味核苷酸,并分析这5种核苷酸在铁观音做青过程中含量的变化规律。结果表明,5种核苷酸的检出限为0.87~1.47μg·g^(-1),定量限为2.62~4.41μg·g^(-1),线性范围为50~1 000 ng·mL^(-1),日内精密度和日间精密度分别为2.17%~4.17%和2.95%~4.74%,回收率为72.89%~91.98%;铁观音茶树品种可检测出UMP、CMP和AMP 3种核苷酸,含量分别为16.98~26.78、14.31~17.56、7.80~9.91μg·g^(-1),由高到低依次为UMP、CMP、AMP,CMP在做青后期缓慢增加;呈味核苷酸总量变化范围为40.78~56.69μg·g^(-1),呈现稳定性波动。该方法快速准确、灵敏度高、稳定性和精密度好,可为茶叶加工过程中风味化学物质分析的研究提供技术支持。

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 0.87-1.47μg·g^(-1),with the limits of quantification of 2.62-4.41μg·g^(-1) and a linear range of 50-1000 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 16.98-26.78μg·g^(-1),the CMP content of 14.31-17.56μg·g^(-1),and the AMP content of 7.80-9.91μg·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 56.69μg·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.