## 3 Results and Discussion  
### TBARS, Oxidation-Reduction Potential (ORP), and pH Value  
Lipid oxidation is the main cause of undesirable chemical and sensory changes resulting in the decreased quality and limited storage of fermented meat products. TBARS is a frequently used indicator to assess the degree of lipid oxidation. Lipid oxidation is one of the main causes of meat products' declined quality and accumulation of harmful end products. One the of most prominent end products is malondialdehydedehyde (MDA), which reacts with thiobarbituric acid (TBA). MDA is linked to the unpleasant aroma of meat products. However, due to the low specificity of TBARS (TBA reacts with multiply compounds), it is difficult to assess the impact of TBARS value on sensory attributes. In general, despite the criticism, for many years, the TBARS index is a commonly used assay to monitor lipid oxidation [57]. In the presented study, TBARS was used to assess the oxidation effect of the studied treatment [15,58,59]. The secondary oxidation products' TBARS values were significantly (\(p<0\),05) affected by the kind of treatment and storage time (Table 1). After production, hams treated with acid whey showed the highest TBARS index (6.07 mg MDA/kg). TBARS values found in the C and the A samples after production were significantly lower (respectively, 3.76 mg MDA/kg and 3.30 mg MDA/kg). After 8 months of storage, the highest TBARS value was also observed in AW samples (6.12 mg MDA/kg) compared to C and A variants (respectively, 3.53 mg MDA/kg and 5.03 mg MDA/kg). The ability of acid whey to inhibit lipid oxidation in fermented meat products can be ineffective [59]. The TBARS in the studied hams shows much higher values than those found by other authors for other fermented meat products. The TBARS values in Iberian dry-cured hams were below 0.60 mg MDA/kg, 1.51-1.59 mg MDA/kg in salted dry-cured turkey hams, 0.86-1.5 mg MDA/kg in Turkish pastirma, a dry-cured beef product, and below 1.6 mg MDA/kg in fermented eye beef round [13; 60; 61; 62]. Refrigerated storage resulted in a significant (\(p<0.05\)) decrease in TBARS value after 3 months in C and AW samples, which may suggest an inhibition in the rate of the oxidation reaction. The decrease in the value of the TBARS index may be related to the reaction of MDA with proteins [63]. In A treatment, an increase in TBARS value was observed during storage, which was statistically significant (\(p<0.05\)) after 3 months. This can indicate that apple vinegar does not prevent oxidation in these hams during storage. The increase in TBARS value during storage could be due to the further oxidation of unsaturated fatty acids and oxidative transformations of primary oxidation products [64]. The acceptable value of TBARS in meat products without oxidized taste aroma should not exceed 2-2.5 mg MDA/kg [65; 66]. However, higher values of the TBARS index (above 2 mg MDA/kg) do not necessarily indicate the poor quality of fermented meat products [67]. Some oxidative changes in raw-ripened meat products can positively impact the development of a desired and distinctive flavor in fermented meat products [68; 69; 70; 71]. The literature on the TBARS index in relation to sensory attributes and the safety of beef products is infrequent. In a recent study, [PERSON] and [PERSON] used artificial neural networks to predict the value of the TBARS index in an assessment of raw beef storage, including the variants of beef enriched with plant-derived antioxidants. The authors reported the usefulness of the developed prediction model for the monitoring of oxidative beef changes; however, they failed to show a correlation between TBARS and plant-derived antioxidant activity [68].