## 3 Results and Discussion
### Relationship between Volatile Compounds, Consumer Scores, and Compositional Analyses  
External preference maps were created to visualize the relationships between the groups of volatile compounds, sensory quality, and other measurements (Figures 3-5). An external preference map for volatile compounds in all cook x muscle treatments (excluding one outlier) explained 66.5% of the variation in the first three principal components (PC; Figure 3a,b). PC1 (36.8%; Figure 3a) differentiates mainly between the two cooking methods on the basis of the quantity of volatiles detected, with most compounds detected to the right of the plot indicating that they were higher in the stewed beef. PC2 and 3 (17.3% and 12.4%, Figure 3b) separate the samples on the basis of the classes of volatile compounds, with most lipid oxidation products (green) to the bottom left and most Maillard products (brown) to the top right of the plot. The stewed beef rather than the roasted beef was associated with Maillard products due to the preparation and sampling methods; the stewed beef was browned before stewing, so some high-temperature compounds would have formed, and the high-temperature Maillard products generated at the surface of the roasted meat would have been lost due to the trimming of the outer surfaces. Flavor liking and overall liking tend to be located to the right side of Figure 3b (to the positive side of PC2), with UMb (USDA marbling score), and are not clearly associated with either of the cooking methods. Figure 3: (**a**) External preference map of stewed and roasted beef samples based on quantities of volatile compounds collected, with consumer scores and compositional analyses plotted on the sameaxes (PC1 vs. PC2). Abbreviations: SM-s--Semimembranosus, stewed; BF-s--Biceps femoris, stewed; RF-s--Bectus femoris, stewed; SM-r--Semimembranosus, roasted; BF-r--Biceps femoris, roasted; RF-r--Rectus femoris, roasted; DMDS--Dimethyl disulfide; DMTS--Dimethyl trisulfide; 2 MeBut--Butanal. 2-methyl; 3 MeBut--Butanal. 3-methyl; 23 But--2.3-butanione; Pent--Pentanal; 2 MeThiop--2-methyl thiophene; 3 Hept-ne--3-Heptanone; 2 Hept-ne;--2-heptanone; Hept--Hept--Heptanal; Benz--benzaldehyde; 2 PeFur--2-Pentyl furan; Oct--Octanal; 2 EtHex--2 ethyl hexanol; Non--nonanal; Oct--octanal; OctAcid--Octanoic acid; FI liking--flavor, liking; UMD--USDA marbling score. (**b**) External preference map of stewed and roasted beef samples based on quantities of volatile compounds collected, with consumer scores and compositional analyses plotted on the same axes (PC2 vs. PC3). Abbreviations: see Figure 3a. Figure 4: (**a**) External preference map of stewed beef samples only (PC1 vs. PC2). Abbreviations: see Figure 3a. (**b**) External preference map of stewed beef samples only (PC2 vs. PC3). Abbreviations: see Figure 3a. There is very little separation of muscles and Figure 3 is dominated by the large differences between the two cooking methods. For this reason, the preference maps were also conducted for the stewed and roasted beef separately (Figures 4 and 5), with three PCs accounting for 68% and 63% of the variation, respectively. Again, PC1 (Figures 4a and 5a) separates the samples mainly on the basis of the overall quantities of volatiles, while PC2 v PC3 (Figures 4b and 5b) separate samples on the basis of the compound group (Maillard products versus lipid oxidation products). Even considering the cooking methods individually, there is no clear separation of muscles and there are no consistent associations between compositional analytes and volatiles. However, the Maillard products (brown) tend to be distinct from the lipid oxidation products (green) in Figures 3b, 4b and 5b. This tendency for compounds from similar reaction pathways to be associated confirms previous results [15,18,34] and is the basis of using marker compounds to represent the different compound classes. Figure 5: (**a**) External preference map of roasted beef samples only (PC1 vs. PC2). Abbreviations: see Figure 3a.