Free amino acids are important metabolites and contributors in green tea quality. Methods were developed to quantitatively analyze free amino acids in particular theanine in tea by Gas Chromatography/Mass Spectrometry (GC-MS) and Gas Chromatography/Flame Ionization Detector (GC-FID). The derivative reagent used in this study was N-tertbutyldimethylsily-N-methytrifluroacetamide (MTBSTFA, ≥95%) with tert- butyldimethylsilyl chloride (TBDMSCl, 1%). Conditions for derivatization (reagent, temperature, time, and acidity) were optimized to give high efficiency. The optimized procedure was as follows: dried amino acids standards or tea extract (water) under N2 gas were re-dissolved in acetonitrile (ACN) and derivatized with MTBSTFA (1:1 to ACN) at 110℃ for 30 min. Analysis of pure amino acid standards showed good linearity (R2≥0.99) within the ranges of 10 to 1 000 nmol. Three peaks were detected for theanine. The MS data indicated that only the third peak (according to peak times) was the completely derivatized product while the first was cyclic and the second was a product of one N-end non-derivatization. Free amino acids in tea sample were quantified by the developed methods and the results were comparable to those analyzed by Amino Acids Autoanalyzer. Recoveries of theanine, alanine, serine, aspartate, glutamate, and glutamine were 85%~108% ranges for spiked tea extract. The developed GC-MS method provided a potential methodology to investigate nitrogen and theanine metabolism in tea plants by quantifying the abundance of 15N labeled amino acids.
ZHANG Jia
,
WANG Chuan-pi
,
RUAN Jian-yun
. Determination of Main Free Amino Acids in Tea by Gas Chromatography-Mass Spectrometry (GC-MS) and Gas Chromatography-Flame Ionization Detector (GC-FID)[J]. Journal of Tea Science, 2010
, 30(6)
: 445
-452
.
DOI: 10.13305/j.cnki.jts.2010.06.007
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