## 3 Results and Discussion  
GC-MS and GC-FID Analyses of Commercial Hop Oils and Hop Oils Hydrodistilled from Commercial Hop Pellets  
GC-MS was used to confirm the identity of seven targeted terpen and methyl hepatomaate contained in seven commercial hop oils and six hop oils hydrodistilled from commercial hop pellets (i) by comparison of their respective retention time (\(t_{\text{R}}\)) values with those of commercial terpene standards, and (ii) by comparison of their mass spectra with those of standards and in the virtual NIST library.  
Quantification of the eight targeted compounds in the hop oils was carried out by GC-FID. Figure 1 shows the chromatograms derived from GC-FID analysis for two hop oils of the same hop variety (Azacca), one commercially obtained and the other hydrodistilled from the hop pellets, as a kind of fingerprint for visual inspection. The parameters of the calibration curves obtained for the eight compounds are summarized in Table 1.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Compound**} & **Retention Time, \(t_{\text{R}}\)** & **Calibration Curve** & **Correlation** & **LOD** & **LOQ** \\  & **[min]** & \(y=ax+b\) & **Coefficient, \(r\)** & **[ng mL\({}^{-1}\)]** & **[ng mL\({}^{-1}\)]** \\ \hline \(\alpha\)-Pinene & 16.1 & \(y=257.4\,x-227.6\) & 0.989 & 0.51 & 1.59 \\ \hline \(\beta\)-Pinene & 17.6 & \(y=256.0\,x-252.7\) & 0.986 & 1.80 & 5.47 \\ \hline \(\beta\)-Myrcene & 17.9 & \(y=233.1\,x-204.6\) & 0.978 & 0.01 & 0.04 \\ \hline Methyl heptanoate & 18.7 & \(y=179.4\,x-156.0\) & 0.955 & 2.26 & 6.86 \\ \hline \(\beta\)-Ocimene & 19.4 & \(y=227.4\,x-140.4\) & 0.963 & 0.58 & 1.76 \\ \hline Limonene & 19.8 & \(y=176.6\,x-164.4\) & 0.977 & 1.87 & 5.66 \\ \hline \(\beta\)-Caryophyllene & 30.5 & \(y=267.2\,x-113.1\) & 0.971 & 2.72 & 8.23 \\ \hline \(\alpha\)-Humulene & 31.1 & \(y=248.2\,x-115.7\) & 0.975 & 20.47 & 62.13 \\ \hline \end{tabular}
\end{table}
Table 1: Retention times (\(t_{\text{R}}\)), calibration curves, and LOD and LOQ values obtained by GC-FID for standard samples of the investigated terpen and methyl hepatomaate (\(n=3\)).  
The contents of the seven terpenenes and methyl heptanoate present in the commercial hop oils and the hydrodistilled hop oils are given in Table 2. From the comparison of quantitative results, it was evident that the differences in the terpene profiles of a set of terpene oils from one technological process (either commercial oils or those hydrodistilled in our lab) were quite similar because all of the investigated hop varieties were from the same botanical species. A distinct feature of the commercial hop oils was a relatively high content of \(\beta\)-myrcene (between 4.21 and 6.40 ug mL\({}^{-1}\) hop oil) in five oils (except Saaz and Ahhhroma). With the hydrodistilled hop oils, the quantitative differences were not very significant either, although Cascade demonstrated an above average content of \(\beta\)-myrcene (6.40 ug mg\({}^{-1}\) dry hop pellet) compared with the remaining varieties. Azacca, Cascade, and Centennial demonstrated perceptibly higher contents of \(\beta\)-caryophylle than the rest, and most hydrodistilled oils (except Chinook) demonstrated relatively high contents of \(\alpha\)-humulene. Some differences between the terpene profiles of individual hop oils presented in Table 2 suggested that the commercial hop oils were derived from hop cones using a process different from hydrodistillation, e.g., solid-liquid extraction with organic solvents or sub- or supercritical fluid extraction with carbon dioxide [46].