# Characterization of the Aroma Profile of Food Smoke at Controllable Pyrolysis Temperatures
## 3 Results and Discussion  
Effect of Controlled Pyrolysis Temperature on the Areas and Ratios of Different Substance Classes in Smoke  
Eighteen characteristic target compounds (Table 1) were selected based on pre-results and literature [6; 13; 14; 15]. While some of the compounds can definitely be derived from wood pyrolysis, e.g., phenols, some other compounds might also be derived from the sausage material as well. Lactones as degradation products of fats and furanones as products from the Maillard reaction are described in non-smoked but heated meat products [1]. However, they are also reported as characteristic smoke constituents and are expected to play important a role in the complex overall flavor of smoke and were therefore included from this research [6]. Nevertheless, it should be mentioned that the sausages produced while smoking might have influenced the aroma composition of the smoke at some point due to the outgassing of specific compounds from the sausage matrix into the smoking chamber. Therefore, subsequent research regarding this phenomenon should be undertaken. \begin{table}
\begin{tabular}{c c c c c} \hline
**No.** & **RI** & **Compound** & **Odor Description 1** & **Quantifier Ion \(m/z\)** & **Identification** \\ \hline carbonyls & & & & \\
1 & \textless{}1000 & diacetyl & butter-like, sweetish, creamy, & & \\  & & & & \\
2 & 1283 & hydroxyacetone & pungent, caramel-like & 43 & RI, MS \\
3 & 1352 & 2-methyl-2- & & & \\  & & cyclopenten-1-one & & & \\
4 & 1808 & cyclotene & sweetish, caramel-like, maple-like, & & \\  & & & sugar-like, coffee-like, woody & & \\ \hline \end{tabular}
\end{table} 
Table 1: Target compounds identified by means of GC-MS after HS-SPME in food smoke. The substance classes carbonyls, lactones and 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]. An increase in carbonyl areas with increasing pyrolysis temperature was reported in observations up to 400 \({}^{\circ}\)C [6,31]. This temperature dependence in the formation of carbonyls, where the substances diacetyl, cyclotene, hydroxyacetone and 2-methyl-2-cyclopent-1-one were included, was shown (Figure 1). A sharp increase in peak area was found during pyrolysis at 150 \({}^{\circ}\)C and 300 \({}^{\circ}\)C, but at further elevated temperatures, there were no longer significant differences in peak area between successive temperature steps. The reaction of carbonyls contained in the smoke with proteins leads to the formation of brown dyes. This non-enzymatic carbonyl-amine reaction is an important process in the formation of the characteristic smoke color [6, 7]. Furthermore, the resulting carbonyls contribute to the flavor. Diacetyl, hydroxyacetone and cyclotene contribute to the caramel-like and sweet smell [32]. Cyclopentanones are attributed a grassy, sweetish and bitter odor [2]. Although phenols are the main constituents of the typical smoky aroma [6], the phenolic fraction alone forms only a monotonous aroma [33]. A round odor profile is created by the additional presence of carbonyls, establishing caramel-like, maggi-like and sweetish odor sensations and therefore providing a fragrant and palatable flavor profile [33,34]. The substance class of lactones also showed a significant increase in peak area within the whole temperature range (Figure 1). The two lactones studied exhibit fatty and oily odor characteristics [32]. No temperature dependence was found for the substance class of furans. The pyrolysis reactions of hemicellulose and cellulose occurring at 275 \({}^{\circ}\)C and above were evident in the carbonyls and lactones, both of which increased when the temperature was raised from 150 \({}^{\circ}\)C to 300 \({}^{\circ}\)C. Contrary to expectations, this could not be shown for furans, which are formed during the dehydrogenation of monomeric