# Characterization of the Aroma Profile of Food Smoke at Controllable Pyrolysis Temperatures
## 3 Results and Discussion
### Effect of Pyrolysis Temperature on the Area and Ratios of Individual Carbonyls and Furans  
In contrast to the phenols and lactones, the carbonyls and furans only showed a medium positive correlation (\(r_{T\text{-}carbonyls}=0.59,p=0.01\)) and, respectively, no linear correlation with the applied pyrolysis temperature. For these two substance classes, the changes in the area of the individual compounds as a function of the pyrolysis temperature were also investigated with the aid of absolute and relative peak areas. The carbonyl cyclotene, which is an important contributor to food flavor formation, increased strongly as the temperature was elevated from 150 \({}^{\circ}\)C to 300 \({}^{\circ}\)C, and then showed a constant peak area (Figure 6a). This indicates heat stability, which may be provided by the ring structure. Hydroxyacetone showed a significantly higher peak area at a pyrolysis temperature of 300 \({}^{\circ}\)C compared to all other temperatures (Figure 6b). For 2-methyl-cyclopenten-1-one (Figure 6c), there was no inference of temperature dependence and diacetyl showed large variations across the temperature spectrum (Figure 6d). Below 450 \({}^{\circ}\)C, hydroxyacetone had the largest share of carbonyls, while above 450 \({}^{\circ}\)C, cyclotene had the largest share. The relative peak areas of each individual carbonyl per applied pyrolysis temperature are given in Table 4.  
Figure 5: Absolute peak areas with standard deviation of individual lactones in food smoke depending on pyrolysis temperature. (**a**) 2-(5H)-furanone and (**b**) butylolactone. Different letters indicate a significant difference in absolute peak area of a substance between different pyrolysis temperatures (\(p<0.05\), \(n=3\)). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Pyalysis Temperature [°C]** & \multicolumn{3}{c}{**Relative Peak Area [\%]**} \\ \hline  & **diacetyl** & **2-methyl-2-cyclopenten-1-one** & **hydroxyacetone** & **cyclidene** \\ \hline
150 & 0.52 \(\pm\) 0.02 \({}^{\rm a}\) & 0.30 \(\pm\) 0.13 & 62.93 \(\pm\) 4.71 \({}^{\rm a}\) & 36.25 \(\pm\) 4.85 \({}^{\rm a}\) \\
300 & 0.65 \(\pm\) 0.06 \({}^{\rm a}\) & 0.38 \(\pm\) 0.11 & 63.25 \(\pm\) 5.50 \({}^{\rm a}\) & 35.72 \(\pm\) 5.10 \({}^{\rm a}\) \\
450 & 0.93 \(\pm\) 0.02 \({}^{\rm b}\) & 0.41 \(\pm\) 0.22 & 32.72 \(\pm\) 1.27 \({}^{\rm b}\) & 65.87 \(\pm\) 12.2 \({}^{\rm b}\) \\
600 & 0.36 \(\pm\) 0.12 \({}^{\rm c}\) & 0.68 \(\pm\) 0.07 & 37.67 \(\pm\) 6.31 \({}^{\rm b}\) & 61.29 \(\pm\) 6.29 \({}^{\rm b}\) \\
750 & 0.64 \(\pm\) 0.27 \({}^{\rm a}\) & 0.68 \(\pm\) 0.41 & 37.69 \(\pm\) 2.98 \({}^{\rm b}\) & 60.99 \(\pm\) 2.27 \({}^{\rm b}\) \\
900 & 0.91 \(\pm\) 0.09 \({}^{\rm a}\) & 0.49 \(\pm\) 0.47 & 32.60 \(\pm\) 3.02 \({}^{\rm b}\) & 66.00 \(\pm\) 2.69 \({}^{\rm b}\) \\ \hline \end{tabular} Different letters indicate a significant difference in absolute peak axes of a substance between different pyrolysis temperatures (\(p<0.05\), \(n=3\)).  
\end{table} 
Table 4: Relative peak areas [°] with standard deviation of individual carbonyls in food smoke depending on pyrolysis temperature. Figure 6: Absolute peak areas with standard deviation of individual carbonyls in food smoke depending on pyrolysis temperature. (a) cyclidene, (b) hydroxyacetone, (c) 2-methyl-2-cyclopenten-1-one and (d) diacetyl. Different letters indicate a significant difference in absolute peak area of a substance between different pyrolysis temperatures (\(p<0.05\), \(n=3\)). Substances belonging to the group of furans are formed by the degradation of hemicellulose and cellulose, which takes place at 200-260 \({}^{\circ}\)C and 280-320 \({}^{\circ}\)C, respectively [6; 13; 14; 15]. During this degradation, monomeric structures are released which are converted to furans by dehydrogenation [35]. One potential formation of the furfural studied here is the degradation pathway of hemicellulose. Released subunits are dehydrogenated at 275-290 \({}^{\circ}\)C and furfural is formed [12].