## 3 Results and Discussion
### Oxidation-Reduction Potential, pH, and TBARS Index
However, the addition of apple vinegar at a 1% level did not significantly affect the ORP values, which were similar to the control sample. After seven days of storage, a significant decrease in the ORP value was observed only in the V3 treatment, while a significant increase in the V1 and V5 treatments was recorded (Table 4). The ORP index value further decreased by 18 mV and 6.6 mV in the C and V5 treatment, respectively, after 14 days of storage compared to the value measured after 7 days of storage (\(p>0.05\)). Acetic acid bacteria are a type of bacteria that undergo oxidative metabolism (\"oxidative bacteria\"). This is because they tend to oxidize certain compounds like ethanol, carbohydrates, and sugar alcohols, resulting in the creation of diverse organic acids, aldehydes, and ketones. The products of these transformations may influence the increase in the oxidation-reduction potential and the amount of secondary fat oxidation products produced [45; 46]. The efficacy of food preservation techniques and the impact of processing on the quality and safety of food can be gleaned through the quantification of secondary products. The TBARS value, which is considered an indicator of the lipid oxidation level, is generally correlated with the off-flavor intensity [47; 48]. The TBARS value of the samples is reported in Table 4.  
Table 4 shows that both apple vinegar and the storage time separately as well as in combination have a significant effect (\(p<0.05\)) on TBARS values. The V3 treatment (with 3% apple vinegar) showed the highest TBARS value of 0.67 mg MDA kg\({}^{-1}\) (\(p<0.05\)), while significantly lower values were found in the V5 treatment (0.55 MDA kg\({}^{-1}\)) directly after production (\(p<0.05\)). After being stored for seven days, the treatment with C showed a lower TBARS value (\(p<0.05\)). However, the treatments with V1 and V5 showed a significant increase (\(p<0.001\)) in the TBARS index value, with the value being higher by 0.1 MDA kg\({}^{-1}\) and 0.14 MDA kg\({}^{-1}\), respectively, compared to the value measured right after production. After fourteen days, no significant differences in the TBARS values (\(p>0.05\)) were found between treatments. However, all treatments showed a significant increase in the TBARS values (\(p<0.05\)) after fourteen days of storage compared to seven days. During the marinating process, free unsaturated fatty acids are oxidized, resulting in secondary oxidation products. These products can have adverse effects on the taste, smell, and safety of the meat. The nutritional value of meat is also reduced due to the loss of essential fatty acids and vitamins resulting from oxidation. Additionally, lipid oxidation produces toxic compounds that are harmful to health. The first change observed due to oxidation is a gradual reduction in the quality of the meat, leading to color, texture, and appearance changes and the development of rancid odors and flavors that affect consumer acceptance. The study did not exceed the threshold for detecting oxidized taste aroma, which in beef is 2 mg/kg [49; 50]. [PERSON] et al. [51] studied the impact of marinating beef steak with different vinegars on its texture, protein profile, and formation of heterocyclic aromatic amines when cooked. However, the marinated and cooked beef steaks did not  
show any significant differences in the TBARS value. According to the authors, the study results can be explained by the reactivity of thiobarbituric acid reactive substances (TBARS) with several compounds present in meat, including protein and amino acids. The reactive nature of TBARS leads to an interaction with these compounds, which sheds light on the observed outcomes. On the other hand, [PERSON] et al. [44] reported that fortifying fresh meat with 5% and 10% of vinegar for preservation at 4 \({}^{\circ}\)C is highly effective.