烘焙條件對烏龍陳茶揮發性成分之影響

Effect of Roasting Conditions on Volatile Composition of Aged Oolong Tea

本研究以氣相層析串聯質譜儀（GC/MS），分析陳年烏龍茶（aged Oolong tea），探討不同焙火模式，對揮發性化合物組成之影響。三種不同焙火模式分別為：60°C×8 h（Mode A）；80°C×4 h（Mode B）；100°C×2h（Mode C），代表淺、中、深（種）焙火。結果顯示，焙火強度影響茶葉揮發物的組成。藉由組合關鍵製程的策略，可以得到截然不同的風味的焙火陳茶。本研究鑑定主要茶葉風味有關之揮發性析出物，探討烘焙模式與揮發物的生成與消失以及含量變化之關聯，結合文獻研究揭露的資訊，探討烘焙模式對烏龍陳茶揮發物特性的影響。研究顯示：淺焙火（Mode A）促進部分低沸點化合物如ethyl acetate、2-bornanone（camphor）的釋放與生成，但保留茶葉原有花果香氣。中焙火（Mode B）導致脂質氧化產生hexanal、2-pentylfuran等氧化產物，呈現穀香與烘焙氣息。重焙火（ModeC）則進入深層熱化學階段，生成芳香萜烴如p-cymene、長鏈酯類如oxalic acid, isobutyl nonyl ester，並出現少量含硫化合物（sulfur compounds），賦予深沉、焦糖與堅果特徵氣味。
揮發物的相對強度趨勢分析顯示三種焙火模式展現不同的揮發物特徵：Mode A以醇、醛等初級氧化物為主，香氣清新；Mode B為反應高峰期，烯烴、酮、酯及芳香族化合物同時達峰，香氣最豐富；ModeC揮發物總量下降，轉為穩定的熟香。不同程度的焙火明顯改變化合物平衡，其中Mode B（中等焙火）為最具代表性或化學活性的烘焙條件。半定量分析提供了與烘焙相關的揮發性成分變化的描述性概述，支持基於趨勢的解釋，而非明確的定量結論。

This study employed gas chromatography–mass spectrometry to investigate the influence of roasting conditions on the volatile composition and aroma characteristics of aged oolong tea. Three roasting conditions that corresponded to light (Mode A), medium (Mode B), and dark (Mode C) roasting modes were applied: heating at 60°C for8 h, heating at 80°C for4 h, and heating at 100°C for2 h, respectively. The results revealed that roasting temperature and duration are critical factors determining the transformation of volatile compounds in oolong tea and the resulting flavor profiles.
A comprehensive analysis was conducted to identify major aroma-related volatiles and track their formation, disappearance, and concentration shifts across roasting modes. Light roasting (Mode A) facilitated the generation of low-boiling-point compounds such as ethyl acetate and 2-bornanone (camphor), preserving the tea’s natural floral and fruity characteristics. Medium roasting (Mode B) intensified lipid oxidation, yielding hexanal and 2-pentylfuran, which generated roasted and cereal-like aromas. Dark roasting (Mode C) induced high-intensity thermochemical reactions, producing aromatic terpenes (e.g., p-cymene), long-chain esters (e.g., oxalic acid isobutyl nonyl ester), and minor sulfur-containing volatiles that imparted caramel-and nut-like aromas.
Comparative analysis of the volatile evolution revealed that each roasting mode resulted in a distinct compositional pattern. Mode A was characterized by the formation of fresh oxidation products (alcohols and aldehydes).Mode B was associated with the greatest compositional diversity, with abundant alkenes, ketones, esters, and aromatics being generated. Finally, Mode C led to a reduction in total volatile content but stable roasting characteristics. Overall, roasting intensity strongly affected the chemical balance and sensory attributes of aged oolong tea, with Mode B representing the optimal conditions for achieving aromatic richness and complexity. The semiquantitative analysis conducted in this study offers a descriptive overview of the volatile composition changes associated with the roasting of aged oolong tea, supporting trend-based interpretation rather than definitive quantitative conclusions.