To investigate the effect of harvesting time on the aroma quality of Langao green tea, volatile compounds in tea leaves collected in early, middle, and late spring were analyzed using stir bar sorptive extraction coupled with gas chromatography-mass spectrometry (GC-MS). Multivariate statistical analysis and odor activity value (OAV) were applied to systematically identify key differential volatile compounds and aroma-active components. A total of 109 volatile compounds were identified, among which terpenes, alcohols, esters, and ketones were the main ones, collectively accounting for 69% of the total volatile content. Principal component analysis, partial least squares-discriminant analysis, and non-parametric tests revealed 23 key differential compounds (P < 0.05) including cis-linalool oxide (furanoid), linalool, cedrol, and 2-methylbutanal, common across different harvesting periods. Based on absolute quantification and OAV analysis, six key aroma-active components (OAV ≥ 1) were identified: 2-methylbutanal, 1-octen-3-one, linalool, α-cubebene, cedrol, and safranal. Among these, linalool and α-cubebene reached the highest concentrations in middle spring, whereas safranal peaked in late spring. These compounds could be used as important indicators for distinguishing Langao green tea from different harvesting periods. This study provides a theoretical foundation for the precise harvesting and quality control of spring tea. Furthermore, it offers potential strategies for enhancing tea quality through targeted modulation of these key aroma compounds.

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 this study, a dynamic headspace (DHS) combined with thermal desorption/gas chromatography-mass spectrometry (TD/GC-MS) method was established to analyze the volatile composition of baked green tea. Extraction parameters including tea amount, trapping temperature, incubation temperature, total purge volume, purge rate, and drying rate were optimized. Furthermore, the key odorants of baked green tea made from different tea cultivars were identified by gas chromatography-olfactometry-mass spectrometry (GC-O-MS). The results indicated that the optimal extraction conditions were as follows: tea amount of 200 mg, trapping temperature of 70 ℃, incubation temperature of 70 ℃, total purge volume of 350 mL, purge rate of 10 mL/min, and drying rate of 10 mL/min. A total of 74 volatile components were identified in green tea made from three representative varieties. Multivariate statistical analysis showed that the aroma compounds of the three green teas varied greatly, and 18 key differential volatile aroma components were identified. The contents of isopropylidesneacetone and linalool in LongJing 43 (LJ 43) baked green tea were the highest among these three teas. Fuding Dabaicha (FDDB) baked green tea contained the highest levels of 6-methyl-5-heptene-2-one, octanal, cyclohexanone, acetophenone, copaene and epicubenol. A total of 28 odorants were identified by GC-O-MS analysis. The odorants were mainly responsible for odor attributes such as green, refreshing, floral, fruity, herbal, woody and sweet aromas. The total aroma intensity of floral and fruity attributes was the highest, followed by the green and refreshing attributes. Taken collectively, linalool, calamenene, δ-cadinene, 6-methyl-5-heptene-2-one and octanal were the key differential odorants among the three green teas. Linalool contributed significantly to LJ 43 baked green tea, and the other four odorants contributed significantly to the formation of the aroma quality of FDDB baked green tea.

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.