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.

In order to explore the differences in the aroma components of baked green tea harvested in different seasons, the composition and content of volatile components in spring and autumn green tea processed from three major tea cultivars in Zhejiang province were systematically analyzed via stir bar sportive extraction (SBSE) combined with gas chromatography-mass spectrometry (GC-MS). Then, key differential volatile components and key aroma-active components were selected by multivariate statistics and odor activity value (OAV) analysis. Results showed that a total of 105 volatile components were identified in spring and autumn green tea, and alcohols, esters and ketones accounted for more than half of the total number. Through principal component analysis (PCA), partial least squares-discriminant analysis (PLS-DA) and significance analysis, 38 compounds such as phytol, 1-octanol and 1-octen-3-ol were found to be the key compounds with statistical differences in spring and autumn green tea (P < 0.05). Combining the results of quantitative analysis and OAV, phytol, hexanal, nonanal, 1-octen-3-ol, octanal and trans-β-ionone were identified as the key aroma active components in baked green tea (OAV > 1). The concentration of phytol in autumn tea samples (967.65 ng/mL) was significantly higher than that in spring tea samples (370.82 ng/mL). It might be related to the sufficient chlorophyll reserve in fresh tea leaves harvested in autumn. However, the concentrations of hexanal and other components were generally higher in spring tea, which might be related to the seasonal changes of enzyme activities related to the formation of fatty acids or carotenoid derivatives.