关键词: 季节；凌云白毫绿茶；香气成分；动态顶空-气相色谱-质谱；偏最小二乘-判别分析

Abstract: This study aimed to understands the main aroma components of Lingyun pekoe green tea and to explore the differences in aroma components among different harvest seasons. Dynamic headspace-gas chromatography-mass spectrometry (DHS-SPME-GC-MS) was used to determine the aroma components of Lingyun pekoe tea in spring, summer and autumn. Based on the relative content of each aroma component, we used partial least square-discriminant analysis (PLS-DA) to establish discriminant models for tea samples harvested in different seasons, then found out the aroma components crucial to tea sample classification, and finally drew a heat map to determine the distribution pattern of the key aroma components in different harvest seasons using hierarchical cluster analysis (HCA). Results showed that a total of 37 compounds were identified in the tea samples, the predominant ones being alcohols and aldehydes. The main aroma components were linalool, n-amyl alcohol, geraniol, L-menthol, isobutyraldehyde, isoglutaraldehyde, nonaldehyde, ethyl acetate, dimethyl sulfide and indoles. The established PLS-DA model could obviously distinguish tea samples harvested in the three seasons, with good reliability. A total of 12 aroma components, nonaldehyde, betarecolone, l-menthol, 3,5-octadiene-2-ketone, trans-orange-flower tert alcohol, benzyl alcohol, n-amyl alcohol, tridecane, cis-2-pentene-1-alcohol, cis-jasmonone, tetradecane and leaf alcohol were identified as the key compounds to distinguish Lingyun pekoe tea in different seasons. Collectively, the heat map and cluster analysis of the 12 aroma components showed that l-menthol and beta-violetone were the most abundant in autumn tea as its characteristic aroma components, which were different from those of spring tea and summer tea and were mainly associated with floral, fruity and peppermint-like aromas. Benzyl alcohol and n-amyl alcohol were the most abundant in spring tea as its characteristic aroma components, which distinguished spring tea from summer tea and autumn tea and mainly contributed to fruity aromas and apricot kernel-like bitter taste. Nonaldehyde, 3,5-octadiene-2-ketone and trans-orange flower tertiary alcohol were the most abundant in summer tea as its characteristic aroma components and were mainly responsible for lemon-like and sweet fruity aroma.

Key words: harvest seasons; Lingyun pekoe green tea; aroma components; dynamic headspace-gas chromatography-mass spectrometry; partial least square-discriminant analysis