部分發酵茶的標準茶葉製程包含以下階段：採茶、日光萎凋、室內萎凋（4次攪拌及靜置）、炒菁、揉捻及乾燥。其中室內萎凋為重要的步驟，因為此步驟直接影響了氧化後的茶香及品質，然而現今部分發酵茶的製茶流程控管主要是依據茶場師傅的嗅覺經驗進行，只要稍有誤判，就會造成茶葉的品質下降，而本研究利用市售的氣體感測器建立電子鼻的系統，希望能建立一套嗅覺感測系統，減少製茶過程中的誤判及人力的消耗。本研究首先利用市售的金氧化半導體氣體感測器建立電子鼻的系統，並將製茶中氣味差異較大的樣品分為三個類別：攪拌前的茶葉（除了第一次攪拌以外）、攪拌後的茶葉及第一次攪拌前的茶葉，其線性判別分析的結果顯示，電子鼻成功將三個類別的樣品分群。接著本研究探討感測器對於茶香中主要4個化合物的選擇性及靈敏度，量測的結果顯示，氣體感測器TGS2603、SP3S-AQ2及SP-53B-00的變動數值最大，因此本研究將原本的14顆氣體感測器篩選至3顆（TGS2603、SP3S-AQ2及SP-53B-00）。最後在監控不同茶葉製程的氣味變化時，本研究發現可以將感測器TGS2603用於監控第四次攪拌的氣味變化。而感測器SP3S-AQ2及SP-53B-00在監控第二次、第三次及炒菁前的氣味變化與人的嗅覺有著非常好的一致性。

The standard process of manufacture semi-fermented tea includes withering, four rounds of shaking and setting （fermentation or oxidation）, firing （fixation）, rolling, and drying. Among all steps, four rounds of shaking and setting （fermentation or oxidation） process are the most important one because they have a large influence on the floral smell and favor of the tea. However, the state-of-the-art method of monitoring oxidation process was conducted by tea masters’ olfactory sensory, and it is difficult to find the optimal timing to shake or set. Then, the wrong timing to shake or set will downgrade the tea quality. This study used a commercial metal-oxide-semiconductor （MOS） gas sensor to establish an electronic nose （E-nose） system, and we applied the E-nose system to measure the samples which have larger difference in grassy smell. We successfully distinguished the grassy smell level between the sample of before shaking, after shaking and before first shaking. Selectivity analysis shows the sensors TGS2603, SP3S-AQ2 and SP-53B-00 have largest variation, therefore the sensors in the E-nose were reduced from 14 to 3. Finally, the on-line monitoring experiment was conducted, and the result showed TGS2603 is suitable for forth shaking process. SP3S-AQ2 and SP-53B-00 is fit to evaluate the smell for 2nd shaking, 3rd shaking and fixation.

[1] S. Hirose, K. Tomatsu, and E. Yanase, "Isolation of key intermediates during formation of oolongtheanins," Tetrahedron Letters, vol. 54, no. 51, pp. 7040-7043, 2013.
[2] M.-C. Menet, S. Sang, C. S. Yang, C.-T. Ho, and R. T. Rosen, "Analysis of theaflavins and thearubigins from black tea extract by MALDI-TOF mass spectrometry," Journal of agricultural and food chemistry, vol. 52, no. 9, pp. 2455-2461, 2004.
[3] E. Schaller, J. O. Bosset, and F. Escher, "‘Electronic noses’ and their application to food," LWT-Food Science and Technology, vol. 31, no. 4, pp. 305-316, 1998.
[4] J.-E. Haugen, "Electronic noses in food analysis," Headspace analysis of foods and flavors, pp. 43-57, 2001.
[5] J. Gonzalez, P. t. Coggon, and G. Sanoerson, "A Research Note Biochemistry OF Tea Fermentation: Formation Of T‐2‐Hexenal From Linolenic Acid," Journal of Food Science, vol. 37, no. 5, pp. 797-798, 1972.
[6] T. Tanaka and I. Kouno, "Oxidation of tea catechins: chemical structures and reaction mechanism," Food Science and Technology Research, vol. 9, no. 2, pp. 128-133, 2003.
[7] Y. Wang et al., "Simultaneous determination of seven bioactive components in Oolong tea Camellia sinensis: quality control by chemical composition and HPLC fingerprints," Journal of agricultural and food chemistry, vol. 60, no. 1, pp. 256-260, 2012.
[8] S.-Y. Lin, L.-C. Lo, I.-Z. Chen, and P.-A. Chen, "Effect of shaking process on correlations between catechins and volatiles in oolong tea," journal of food and drug analysis, vol. 24, no. 3, pp. 500-507, 2016.
[9] A. Kobayashi, K. Tachiyama, M. Kawakami, T. Yamanishi, I.-M. Juan, and W.-F. Chiu, "Effects of solar-withering and turn over treatment during indoor-withering on the formation of pouchong tea aroma," Agricultural and Biological Chemistry, vol. 49, no. 6, pp. 1655-1660, 1985.
[10] J. Tsay and W.-C. Chang, "Effects of agitation on tea flush during withering process of Paochong tea," in Proceedings of 2001 international conference on OCHA (Tea) culture and science, 2001, p. 98e100.
[11] N. Subramanian, P. Venkatesh, S. Ganguli, and V. P. Sinkar, "Role of polyphenol oxidase and peroxidase in the generation of black tea theaflavins," Journal of agricultural and food chemistry, vol. 47, no. 7, pp. 2571-2578, 1999.
[12] A. Dey, "Semiconductor metal oxide gas sensors: A review," Materials Science and Engineering: B, vol. 229, pp. 206-217, 2018.
[13] 周瑞福, "氣體感測器原理與應用," 三聯科技股份有限公司.
[14] W. Weppner, "Solid-state electrochemical gas sensors," Sensors and Actuators, vol. 12, no. 2, pp. 107-119, 1987.
[15] M. L. Langhorst, "Photoionization detector sensitivity of organic compounds," Journal of Chromatographic Science, vol. 19, no. 2, pp. 98-103, 1981.
[16] T. Lin, Y. Li, H. Hao, I. Fang, C. Yang, and D. Yao, "Surface acoustic wave gas sensor for monitoring low concentration ammonia," in 2011 16th International Solid-State Sensors, Actuators and Microsystems Conference, 2011: IEEE, pp. 1140-1143.
[17] N. Bhattacharyya et al., "Detection of optimum fermentation time for black tea manufacturing using electronic nose," Sensors and Actuators B: Chemical, vol. 122, no. 2, pp. 627-634, 2007.
[18] N. Bhattacharyya et al., "Monitoring of black tea fermentation process using electronic nose," Journal of Food Engineering, vol. 80, no. 4, pp. 1146-1156, 2007.
[19] N. Bhattacharya, B. Tudu, A. Jana, D. Ghosh, R. Bandhopadhyaya, and M. Bhuyan, "Preemptive identification of optimum fermentation time for black tea using electronic nose," Sensors and Actuators B: Chemical, vol. 131, no. 1, pp. 110-116, 2008.
[20] N. Bhattacharyya, R. Bandyopadhyay, M. Bhuyan, B. Tudu, D. Ghosh, and A. Jana, "Electronic nose for black tea classification and correlation of measurements with “Tea Taster” marks," IEEE transactions on instrumentation and measurement, vol. 57, no. 7, pp. 1313-1321, 2008.
[21] 賴正南(編), "茶葉技術推廣手冊-製茶技術," p. 90, 2001.
[22] X.-T. Yin, J. Li, D. Dastan, W.-D. Zhou, H. Garmestani, and F. M. Alamgir, "Ultra-High Selectivity of H2 over CO with a pn Nanojunction based Gas Sensors and its mechanism," Sensors and Actuators B: Chemical, p. 128330, 2020.
[23] W.-d. Zhou et al., "Optimization of gas sensing properties of n-SnO 2/p-x CuO sensors for homogenous gases and the sensing mechanism," Journal of Materials Science: Materials in Electronics, vol. 31, no. 21, pp. 18412-18426, 2020.
[24] S. Nie et al., "Gas-sensing selectivity of n-ZnO/p-Co3O4 sensors for homogeneous reducing gas," Journal of Physics and Chemistry of Solids, vol. 150, p. 109864.
[25] K. Shan et al., "Diffusion kinetics mechanism of oxygen ion in dense diffusion barrier limiting current oxygen sensors," Journal of Alloys and Compounds, vol. 855, p. 157465, 2021.
[26] K. Shan et al., "Mixed conductivities of A-site deficient Y, Cr-doubly doped SrTiO3 as novel dense diffusion barrier and temperature-independent limiting current oxygen sensors," Advanced Powder Technology, 2020.
[27] X.-T. Yin, D. Dastan, F.-Y. Wu, and J. Li, "Facile synthesis of SnO2/LaFeO3− XNX composite: photocatalytic activity and gas sensing performance," Nanomaterials, vol. 9, no. 8, p. 1163, 2019.
[28] W.-D. Zhou, D. Dastan, J. Li, X.-T. Yin, and Q. Wang, "Discriminable Sensing Response Behavior to Homogeneous Gases Based on n-ZnO/p-NiO Composites," Nanomaterials, vol. 10, no. 4, p. 785, 2020.
[29] X.-T. Yin et al., "Nanostructured tungsten trioxide prepared at various growth temperatures for sensing applications," Journal of Alloys and Compounds, vol. 825, p. 154105, 2020.
[30] N. Barsan and U. Weimar, "Understanding the fundamental principles of metal oxide based gas sensors; the example of CO sensing with SnO2 sensors in the presence of humidity," Journal of Physics: Condensed Matter, vol. 15, no. 20, p. R813, 2003.
[31] J. Zhang, Z. Qin, D. Zeng, and C. Xie, "Metal-oxide-semiconductor based gas sensors: screening, preparation, and integration," Physical Chemistry Chemical Physics, vol. 19, no. 9, pp. 6313-6329, 2017.
[32] X.-T. Yin et al., "A highly sensitivity and selectivity Pt-SnO2 nanoparticles for sensing applications at extremely low level hydrogen gas detection," Journal of Alloys and Compounds, vol. 805, pp. 229-236, 2019.
[33] X.-T. Yin et al., "Tin dioxide nanoparticles with high sensitivity and selectivity for gas sensors at sub-ppm level of hydrogen gas detection," Journal of Materials Science: Materials in Electronics, vol. 30, no. 15, pp. 14687-14694, 2019.
[34] 志尚儀器股份有限公司, "氣體產生器 Series 8000P 簡易操作手冊."
[35] 林書妍, "部分發酵茶茶菁, 製程及成茶中可溶性化學成分與揮發性有機化合物之研究," 園藝學研究所學位論文, 臺灣大學, 2013.
[36] S. Lin et al., "Monitoring volatile compound profiles and chemical compositions during the process of manufacturing semi-fermented oolong tea," vol. 88, no. 2, pp. 159-164, 2013.