# Quality of Sous Vide-Cooked Pork Loin Stored in Refrigerated Conditions
## 3 Results and Discussion
### Lipid Oxidation  
Lipids present in processed meat are in great extend responsible for its desirable sensory attributes, such as flavour, texture, and juiciness. Nevertheless, they are susceptible to the oxidative processes caused by elevated temperatures and presence of oxygen [20]. In the present study, lipid oxidation in sous vide-cooked pork loin during refrigerated storage was evaluated with the use of TBARS index, which reflects the presence of thiobarbituric acid reactive substances derived mainly from lipids secondary oxidative reactions and is highly correlated with sensory evaluation scores [32]. Oxidative changes in meat, determined shortly after heat treatment at day 0 and at days 3 and 7 during refrigerated storage, are presented in Figure 1. In general, the increasing tendency in TBARS values was noted with increasing heat treatment temperature, as well as extended time of storage. At day 0, samples cooked at 57 \({}^{\circ}\)C/5.5 h, 59 \({}^{\circ}\)C/4.5 h, and 60 \({}^{\circ}\)C/4 h showed significantly lower TBARS values (1.47-1.59 mg MDA/kg) than samples cooked at 61 \({}^{\circ}\)C/4 h and 63 \({}^{\circ}\)C/3.5 h (1.75-1.78 mg MDA/kg). At day 3, only sample cooked at the lowest temperature was characterised by the TBARS value significantly lower (1.54 mg MDA/kg) than samples cooked at 61 and 63 \({}^{\circ}\)C (1.81-1.83 mg MDA/kg) and the same tendency was observed after 7 days of storage (1.58 mg MDA/kg vs. 1.82-1.84 mg MDA/kg, resp.). The decline in TBARS value observed for 60 \({}^{\circ}\)C/4 h treatment after 7 days of storage may result from natural changes occurring in the meat during storage, such as oxidative processes, water loss, or interactions between different compounds present in meat. Malondialdehydedehyde (MDA), which is one the secondary products of lipid oxidation and one of the main contributors to TBARS value [33], is highly reactive, and while, in general, its amount increases as a result of oxidation, it simultaneously reacts with other compounds present in meat, which makes it not detectable in TBARS assay [34]. Therefore, the TBARS values observed for stored meat products do not change in an unambiguous way but rather fluctuate [35], which presumably might have been the reason for the decrease observed in our study for the sample treated at 60 \({}^{\circ}\)C/4 h. Therefore, the highest TBARS values were recorded for samples heated at temperatures of 61 \({}^{\circ}\)C and 63 \({}^{\circ}\)C, which indicates more intense lipid oxidation at higher temperatures. It was shown that the TBARS values of samples were significantly influenced by treatment conditions (\(p<0.001\)) and storage time (\(p<0.01\)), but not by the interaction between them. A comparison of the TBARS value of raw meat (0.65 mg MDA/kg) and TBARS values of meat sous vide cooked and stored in refrigerated conditions (1.47-1.84 mg MDA/kg) suggests that heat treatment was the main contributor to the oxidative changes in meat products observed during short term storage in our study. Slight increases in TBARS values during storage of samples could be attributed to the presence of residual oxygen in the packages [36]. [PERSON] et al. [23] observed an accelerated lipid oxidation in sous vide-cooked chicken breast compared to vacuum packed raw meat over the same refrigerated storage period. It can be seen that vacuum storage may delay, but does not completely prevent, lipid oxidation [37; 38]. In the study by [PERSON] et al. [22], pork loin was cooked using sous vide method at 70 \({}^{\circ}\)C/12 h, then stored at 2 \({}^{\circ}\)C, and evaluated after cooking and after 5 and 10 weeks of storage. The authors observed a significant increase in the TBARS value after 5 weeks storage and a significant decrease in this value after 10 weeks storage, but all TBARS values were below 1 mg MDA/kg. Increasing and fluctuating TBARS values, but lower than 2 mg MDA/kg, were also observed for marinated, sous vide-cooked, and stored up to 8 weeks pork loin by [PERSON] et al. [39].