本研究利用熱脫附儀串聯氣相層析質譜儀(TD-GC-MS)分析不同烘培程度的咖啡豆風味，並搭配Tenax-TA吸附管以及低流量的採樣幫浦進行咖啡氣味的採樣。不同烘培條件賦予咖啡豆不同的風味，這些風味成分主要是經由烘培過程中所發生的一系列化學反應而形成。我們利用GC-MS鑑定出17種咖啡豆的主要風味成分，結果顯示大部分成分都隨烘培程度而增加，但Furfurals類的成分卻隨著烘培程度下降。
　　另外，我們也提出在烘培中可能發生的化學反應機制與途徑，加以說明風味成分的變化與趨勢。咖啡豆的存放時間和量測間隔也會影響實驗結果，不同風味成分有不同的隨著存放時間的變化趨勢，而成分的分子量、沸點、與化學結構可能是影響變化趨勢的主要因素；由2-methyl-furan的變化趨勢來看，量測間隔越長，成分的下降速度較為緩慢。

　　This research was to demonstrate the TD-GC-MS system and realize the idea of gas measurement and analysis, roasted coffee beans were chosen as our study target. Tenax-TA adsorbent tubes and a low flow rate pump were used to collect the coffee beans aroma. Then the adsorbent tube was submitted to TD-GC-MS for analysis. Different roasting conditions would give the coffee beans aroma various smells and taste characteristics. This is due to the complex chemical reactions occurred during the roasting process. 17 major components have been identified by GC-MS. Results showed that most components in coffee beans aroma increased with roast levels, while furfurals family had a downward tendency. A mechanism of the formation of furfural was proposed to explain the decrease in furfural. Storage time and monitoring intervals were also two factors that can affect the measurement results. Components had their own specific trends of change in their intensity over the storage period. This can be due to the molar mass, boiling points, and chemical structures. As the monitoring intervals prolonged, which means less sampling frequency, we found that the intensity of 2-methyl-furan significantly decayed at a slower rate.

Chapter 1 Introduction 1
Chapter 2 Literature Review 5
2.1 Methodologies for Gas Analysis 5
2.1.1 Tunable Diode Laser Absorption Spectroscopy (TDLAS) 5
2.1.2 Open-Path FTIR (OP-FTIR) 6
2.1.3 Proton-Transfer Reaction-Mass Spectrometry 7
2.1.4 Gas Chromatography and Mass Spectroscopy (GC-MS) 7
2.2 Related Researches of Analyzing Coffee Beans Aromas Using GC-MS 8
2.2.1 How Many Components in Coffee Beans Aromas? 8
2.2.2 Investigation of Roasting Conditions 9
2.2.3 Investigation of Storage Time 10
2.3 Methods of Sample Pre-treatment and Sample Introduction 11
2.4 Thermal Desorption (TD) 11
2.4.1 TD History 12
2.4.2 TD Applications 13
2.4.3 Why Thermal Desorption (TD)? 13
2.5 Sampling Techniques Comparison 15
Chapter 3 Experimental 17
3.1 Introduction of Sampling Tube (Tenax-TA) 18
3.1.1 Multi-Bed Adsorbent Sampling Tube 18
3.1.2 Preparation and Conditioning for Sampling Tubes 19
3.1.3 Tenax Adsorbent 20
3.2 Instrument and Analytical Parameters 20
3.2.1 Thermal Desorber (TD) 20
3.2.2 Gas Chromatography/Mass Spectrometry (GC-MS) 23
3.3 The Roasting Condition of Coffee Beans 23
3.4 Data Obtained from GC-MS 25
3.4.1 Retention Time 25
3.4.2 Peak Height 25
3.4.3 Peak Area 25
3.4.4 Area% and Height% 26
3.5 Adjusting Sampling Method to Optimize the Measurement Results 27
3.5.1 Is Sequence Analysis Available? 27
3.5.2 Does Sampling Distance Affect the Measurement Result? 29
Chapter 4 Results and Discussion 31
4.1 Standard Gas for Quantitative Analysis 31
4.1.1 Diluting the Isobutene Standard Gas to Different Concentrations 31
4.1.2 Adjustment of the Mass Flow Controllers 32
4.1.3 Drawing the Calibration Curve for Isobutene Standard Gas 34
4.2 Analysis of Coffee Beans Aromas 35
4.2.1 Using Peak Area for Quantitative Analysis 35
4.2.2 Major Compounds in Coffee Beans Aroma 35
4.2.3 Gas Chromatograms of Coffee Beans Aromas 36
4.3 Changes of Aroma Intensity during Storage 39
4.4 The Effect of Monitoring Intervals 49
4.4.1 The Trends of Intensity Change in 2-methyl-furan 49
4.4.2 The Trends of Intensity Change in Other Components 51
4.5 Comparison of Different Roast Levels 56
4.6 PCA Analysis for Coffees According to the Roast levels 60
4.7 Furfurals Removal from Roasted Coffee Beans 65
4.8 Chemical Reactions in Roasting Process 67
4.8.1 Roasting 67
4.8.2 Chemical Reactions during the Roasting Process 68
Chapter 5 Conclusion and Future Perspectives 79
Chapter 6 References 81

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