# Quality of Sous Vide-Cooked Pork Loin Stored in Refrigerated Conditions
## 3 Results and Discussion
### Volatile Compounds  
The flavour of cooked meat is a combined effect of its taste and aroma. Compounds responsible for those meat characteristics are naturally present in meat or are generated during meat heat treatment, mainly as a result of Maillard reactions and oxidation of lipids [11]. The analysis of volatile compounds in pork loin using gas chromatography coupled with ion mobility spectrometry (HS-GC-IMS) allows for the precise identification and qualitative determination of the compounds responsible for the aroma. Changes in the profile of volatile compounds can be directly related to the perception of freshness, storage stability, and sensory quality of meat. The influence of sous vide processing and storage time on these compounds in pork loin was analysed in the context of different temperatures and processing times, and storage periods of 0, 3, and 7 days. Principal component analysis (PCA) was used to understand patterns and relationships between different samples. PCA allowed to reduce the dimensionality of data, while simultaneously highlighting the most important variables influencing differences in meat quality after processing and during storage [66; 67]. Only 16 volatile compounds were found in raw meat, while in meat heat-treated at temperatures of 57-63 \({}^{\circ}\)C, 29 compounds were identified (Figure 2). Peak intensity for 3-methyl-1-pentene, 2-propanethiol, isobutyl methyl ether, 2,3-butananedione, but-2-enal, 1-butanol, pentanal, 3-methyl-2-buthenal, 1,3-butanediol, heptanal, 2-ethyl-6-methylpyrazine, and 2-decanone increased with increasing thermal treatment temperature. Pentanal, hexanal, heptanal, and octanal are linear aldehydes, which were the dominant volatile aldehydes generated in cooked pork. These compounds were formed as a result of lipid oxidation that occurred during meat cooking and storage, as demonstrated by TBARS analysis (Table 1). A significant increase in pentanal, hexanal, heptanal, octanal, and nonanal, in sous vide cooked lamb loin compared to raw meat was reported by [PERSON] et al. [40]. Hexanal and heptanal are derived mainly from linoleic and arachidonic acid oxidation, whereas octanal is generated as a product of oleic acid oxidation [46]. These compounds are responsible for the grassy and fruity aromas of meat [68]. It was also suggested that hexanal is a more effective indicator of lipid oxidation in meat than other volatile compounds [32]. Ketone compounds such as acetone, 2,3-butananedione, 2,3-pentanedione, and 2,3-hexanedione were present in raw meat and generally increased in concentration after heat treatment. The increase in ketone levels during cooking can be attributed to the breakdown of fatty acids and amino acids, which is more visible under the influence of heat. Unlike aldehydes, which are formed mainly during lipid oxidation, ketones can originate from both the degradation of unsaturated fatty acids and Maillard reactions [46]. However, in our study, Maillard reactions could have had only a limited contribution to the increase in ketone concentration since the relatively low heat treatment temperatures applied in our study did not favour those reactions [11]. Similar research results were obtained for other types of meat where ketone levels were increased, which additionally contributed to the complex flavour profile of cooked meat. For example, the study by [PERSON] and [PERSON] [69] found that the content of ketones, such as 2,3-butanedione and 2,3-pentanedione, increased significantly when meat was cooked, enhancing the buttery and creamy notes of meat aroma. [PERSON] et al. [46] reported the presence of 2,3-octanedione and 2-cyclopentanone as the main ketones observed in braised pork. As for alcohols, although they are derived from the oxidation of fatty acids, they have higher aroma thresholds and are generally not considered important factors affecting the aroma of meat products [46]. For comparison, in the study by [PERSON] et al.