# Characterization of the Aroma Profile of Food Smoke at Controllable Pyrolysis Temperatures
## 1 Introduction  
Food smoking is a very popular process in food production. In Germany, for example, 60% of all meat products produced are treated with food smoke [1]. Triggered by current developments in consumers behavior and demands for food (healthy, natural, clean label), as well as current world developments, the meat industry is currently questioning the standardized smoking processes and is looking for alternative processes with a low energy input, as well as individual product development for unique products. Therefore, it is mandatory to better understand the single and overall substance-process-function relationship while smoking. Wood smoke, used in food processing, is produced from the thermal decomposition of wood, which consists of cellulose (50%), hemicellulose (25%) and lignin (25%) [2]. Smoke represents a complex multi-phase system consisting of a gas phase, called the vapor phase, and a dispersed particle phase with liquid or solid particle droplets [3, 4, 5]. It includes air, water vapor, carbon dioxide, carbon monoxide and nitrogen oxide, and over 400 volatile compounds have been identified in food smoke, containing phenols, carbonyls, acids, furans, esters, alcohols, lactones and other compounds [5, 6]. Phenols, carbonyls and furrans are the main substance classes contributing to flavor formation, with phenols being mainly responsible for the food smoke flavor [2]. Carbonys have an important role in color and texture development [6, 7]. Due to the antimicrobial and antioxidant properties of some smoke compounds, food smoke has a preservative effect. Many compounds, such as phenols, carbonyls and acetic acid, have antimicrobial activity on their own and actsynergistically when they coexist, as is the case in smoke [8; 9]. The phenols are formed from the thermal pyrolysis of lignin, while carbonyls, furans, acids and other volatile compounds originate from the thermal degradation of hemicellulose and cellulose [6; 10; 11; 12; 13]. The degradation of hemicellulose, cellulose and lignin each takes place in a specific temperature range and thus the degradation products are formed characteristically for applied pyrolysis temperatures [6; 13; 14; 15]. Consequently, the applied pyrolysis temperature can influence the compounds of smoke and thus the techno-functional properties of the generated smoke. These techno-functional properties include the typical color, texture, shelf-life, smell and taste for the smoked products [6; 7; 16]. Despite the vast number of technologically important characteristics that are generated by smoking food, at present, the controlled generation of smoke is not possible, as the smoke in the smoldering smoke generators currently used in industry is generated under constant plant parameters without further process control [17]. Thus, only the parameters in the smoke chamber where the product is located can be adjusted, but not the smoke generation parameters. Therefore, a newly designed smoldering smoke generator is used, in which pyrolysis temperature, supply airflow during smoke generation and moisture content of the wood can be varied. With this newly designed smoke generator, it is possible to generate smoke in a targeted process and thus to achieve the product-specific techno-functional and sensory properties. Headspace solid-phase microextraction (HS-SPME) offers the possibility to perform a solvent-free, simple, fast, sensitive and reproducible extraction of volatile analytes [18; 19; 20; 21]. HS-SPME was shown to be suitable in the analysis of phenols in food smoke [22]. Among the various coating materials of fibers available, DVB/CAR/PDMS shows a high extraction efficiency for substances with high retention indices in smoked food [23].