5 ArroqueñoMezcal
upon accurate mass and isotope data. GC-MS is the classical approach to separate and identify isomers in a mixture. Quadrupole mass spectrometers like the Q1500 GC are widely used for GC-MS analysis because of their low cost and ease of operation and maintenance. Compounds are identifi ed by searching EI mass spectra against the mass spectral databases and using retention index matching to distinguish isomers having similar database search scores.
Chromatographic deconvolution and statistical analysis were carried out by using AnalyzerPro XD software (SpectralWorks Ltd) which provides powerful and easy-to-use capabilities for chemometric analysis of GC-MS data from the JEOL Q1500GC GC-MS system. AnalyzerPro XD analysis identifi ed differences in the aroma composition between each of the beverages.
Hornitos Reposado Tequila
Three replicate measurements (the minimum number required for statistical analysis) were made for each of three mezcal samples (Arroqueño, Tobala, and Ensamble) and the reposado tequila.
The volcano plot and bar graph in Figure 4 shows that isobutyl acetate is present at signifi cant amounts only in Arroqueño mezcal and reposado tequila.
Figure 1. Negative-ion DART mass spectra for Arroqueño mezcal (top) and reposado tequila (bottom).
Principal Component Analysis (Figure 2) shows clustering of the mezcals visible in three dimensions, but the tequila sample is clearly distinguished from the mezcals. The two Ensamble samples are clearly different. Leave-One-Out Cross Validation (LOOCV) for Support Vector Machine (SVM) classifi cation shows 100% accuracy for identifying the mezcals and tequila.
Figure 4. Volcano plot comparing tequila and Ensamble mezcal and bar graph showing the distribution of isobutyl acetate in 3 mezcals and one tequila.
The Principal Component Analysis (PCA) graph and biplot in Figure 5 show that the four different beverages have distinctive aroma profi les. The same fi gure shows that ethyl propionate (pineapple aroma) is present in all three mezcals, but absent in the reposado tequila.
Figure 2. Principal Component Analysis of the mezcal and tequila samples.
We can view sample-dependent variations for individual components by using box plots or volcano plots. The top image in Figure 3 shows the box plot for m/z 107.049 corresponding to deprotonated cresol and guaiacol, two of the components that gives mezcal a smoky aroma and taste that differentiate it from tequila. Cresol and guaiacol are present in all mezcal samples, but absent in the reposado tequila. The bottom image shows the box plot for deprotonated octanoic acid and vanillin which are indicators of tequila maturation [3].
Figure 5. Principal Component Analysis and distribution of ethyl propanoate in the mezcals and tequila.
Box Plot for 107.04969, Cresol-H; 2.5 Ensamble_new
1.5 2
0.5 1
0 Hornitos_Reposado Tobala Arroqueno Ensamble 0.4 Hornitos_Reposado 0.2 0 0.6 Tobala 0.8 Arroqueno Ensamble Ensamble_new
The box plots in Figure 6 show the differences in the distribution of the two isomers 2-methyl-1-butanol with an odour described as ‘roasted winey onion fruity fusel alcoholic whiskey’ [4], and 3-methyl-1-butanol with an odour described as ‘fusel alcoholic pungent ethereal cognac fruity banana molasses’ [5].
Box Plot for 143.10661, Octanoic acid-H;
100 120
20 40 60 80
0 Hornitos_Reposado
2.5 3
1.5 2
Tobala Arroqueno Ensamble Ensamble_new 0
0.5 1
Box Plot for 151.03683, Vanillin-H; Hornitos_Reposado Box Plot for 123.04460, Guaiacol-H;
Tobala Arroqueno Ensamble Ensamble_new
Figure 3. Box plots showing the distribution of selected compounds in the mezcals and tequila.
Single quadrupole GC-MS: Q1500 GC
Ambient ionisation with the AccuTOF-DART provides rapid and convenient analysis and is sensitive to more polar compounds that may or may not be convenient for analysis by gas chromatography. It is a useful approach for differentiating samples and quickly identifying differences. However, assignments for compounds in a complex mixture are based solely
Figure 6. Distribution of two isomers in the mezcals and tequila.
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Tobala
Arroqueno
Ensamble
Hornitos_Reposado Tobala
Ensamble_new Arroqueno
Ensamble
Hornitos_Reposado
Tobala
Ensamble_new
Arroqueno
Ensamble
Hornitos_Reposado Tobala Ensamble_new Arroqueno
Ensamble
Hornitos_Reposado
Ensamble_new
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