啤酒芳香化合物之分析

Abstract

本研究的目的在於建立一套分析啤酒中重要香氣成分的方法，而利用此方法分析市售的臺灣生啤酒。根據文獻回顧，Flavour Dilution (FD) factor，跟 Odour Activity Value (OAV) 可以顯示一個芳香化合物對啤酒香味的貢獻。因此，本研究以十種在啤酒中FD質與OAV較高的化合物作爲目標，建立一個分析方法。研究中探討了有機溶劑萃取的選擇，發現乙醚能夠有效的萃取目標化合物，而萃取率高達 94 醚能夠有效的。跟二氯甲烷相對之下，乙醚也能夠減少目標化合物在減壓濃縮中的流失，降低定量計算的誤差。探討了各個目標化合物在減壓濃縮中不同程度的流失後，此分析方法在計算中以各個化合物的揮發性做調整，確保分析方法的準確性。借由以上的方法，本研究利用 GC-MS分析了臺灣烟酒公司18天生啤酒的芳香化合物，發現結果在一般啤酒的正常範圍内。分析結果顯示，ethyl acetate 的濃度為25.37±0.54 mg/l, ethyl butanoate 低於計算極限，isobutanol 的濃度為14.07±0.34 mg/l，isoamyl acetate 的濃度為1.51±0.05 mg/l，isoamyl alcohol的濃度為60.21±1.61 mg/l，ethyl hexanoate的濃度為0.48±0.02 mg/l，ethyl octanoate的濃度為0.57±0.02 mg/l，3-methylthio 1-propanol的濃度為2.10±0.03 mg/l，2-phenylethyl acetate的濃度為0.44±0.01 mg/l，2-phenylethyl alcohol的濃度為23.89±0.43 mg/l。此外，該研究也探討了這十種芳香化合物經過存放的變化，發現各個化合物都有減低的現象，尤其在第18天之後。

The objective of this study is to establish a protocol to quantitate important aroma compounds found in beer and subsequently, to conduct the analysis on draft beer sold commercially in Taiwan. Flavour dilution (FD) factor and odour activity value (OAV) are generally recognized as a reliable indicator of a compound’s contribution to aroma. Therefore, 10 aroma compounds which were commonly observed to have high OAV and FD factors in beer were chosen to be the target analytes from which a protocol for their analysis could be established. Diethyl ether was found to be a suitable choice of solvent for the extraction of the target analytes in beer with extraction rates ranging from 94 to 100%. The analyte loss during solvent removal was also found to be less than that when using dichloromethane, therefore reducing the margin of error during quantitation. By studying the difference in volatilities of the target analytes, the differences in analyte loss during solvent removal was able to be accounted for by dividing the analytes into low, medium and high volatilities. Using this method, 18 day draft beer from Taiwan Tobacco and Liquor Corporation was analysed using Gas Chromatography – Mass Spectrometry (GC-MS) and the concentrations of the target analytes were found to be comparable to that of typical beers. The concentration of ethyl acetate was found to be 25.37±0.54 mg/l, ethyl butanoate was too trace to measure, isobutanol was 14.07±0.34 mg/l, isoamyl acetate was 1.51±0.05 mg/l, isoamyl alcohol was 60.21±1.61 mg/l, ethyl hexanoate was 0.48±0.02 mg/l, ethyl octanoate was 0.57±0.02 mg/l, 3-methylthio 1-propanol was 2.10±0.03 mg/l, 2-phenylethyl acetate was 0.44±0.01 mg/l and 2-phenylethyl alcohol was 23.89±0.43 mg/l. The change in these aroma compounds were tracked over and beyond the mandated shelf life of 18 day draft beer and it was found that they exhibited a general decreasing trend, especially once past the 18 day mark.