Comparative Analysis of Quality Components in Baked Green Tea Made from Tea Plants Grown at Different Altitudes

In order to explore the relationship between altitude and the major quality components of tea, the contents of the major non-volatile chemical components tea polyphenols and amino acids, as well as the composition and content of aroma components in baked green tea samples made from tea plants from different altitudes were analyzed. Then, the key components that significantly differed among tea samples were identified by multivariate statistical analysis, and their correlation with altitude was evaluated. Results showed that there was a statistical significant difference in the total amount of free amino acids among tea samples (P < 0.05), and that the contents of theanine, glutamine, threonine, serine and arginine in the high-altitude group (650–1102 m) were significantly higher than in the low-altitude group (400–600 m). A total of 298 aroma components were identified from all samples, including aldehydes, alcohols, alkenes, alkanes, ketones, aromatic hydrocarbons, organic acids, esters, lactones, phenols, alkynes, amines, ethers, oxygen heterocyclic compounds, nitrogen compounds and sulphur compounds, with aldehydes and alkanes being the most abundant ones. The results of partial least squares discriminant analysis (PLS-DA), cluster analysis and correlation analysis indicated that the contents of quality components significantly differed (P < 0.05) between the low- and high-altitude groups, and 26 differential aroma compounds such as 3-methylbutanenitrile, α-phellandrene and indole were identified. It was also shown that the contents of total free amino acids, theanine, glutamine, threonine, serine and arginine as well as 3-methylbutanenitrile were higher in the high-altitude group than in the low-altitude group, while the opposite was observed for the contents of 25 aroma compounds such as α-phellandrene and indole. Furthermore, correlation analysis indicated that the contents of theanine, serine, threonine and total free amino acids had a significantly positive correlation with sensory taste scores. Nine aroma compounds including (Z)-2-heptenal, 3-penten-2-one, 4-methyloctane, 3-ethyl-heptane, 1-octen-3-one, α-phellandrene, (E,E)-2,4-heptadienal, 3,4-dimethylfuran-2,5-dione and 4-methylindan had a significantly negative correlation with altitude. It was speculated that the formation and accumulation of aroma precursors may be related to altitude.