# Influence of LAB Fermentation on the Color Stability and Oxidative Changes in Dry-Cured Meat
## 4 Discussion
SH groups are one of the most reactive functional groups in proteins, and SH groups of sulfur-containing amino acids (e.g., cysteines) are easily oxidized by hydroxyl radicals, thus forming intra- or intermolecular disulfide bonds [34; 47]. Therefore, SH is another indicator of volatilization in muscle proteins [48]. In this study, free SH groups were probably oxidized to disulfide bonds, creating a relatively tight structure of the protein network. Due to the formation of protein networks, hydrophobic amino acids were probably buried in particles, which led to reduced hydrophobicity [49], as was observed in C, LOCK, and BB tests. A slightly different trend was observed in the BAUER test in which a systematic increase in the HS parameter was observed, reaching the highest surface hydrophobicity in all variants after 12 months (Figure 1) and a simultaneous increase in the SH value (Figure 2). Generally, in the first period of the analysis (in the 6 th month), the effect of BAUER on the reduction in the SH content was observed (\(p>0.05\)),whereas the remaining strains did not affect the SH content compared with the control (C; \(p<0.05\)). The reduction in the SH content observed in BAUER samples was probably related to the oxidation of cysteine SH groups to form disulfide bonds [28]. In the present study, a decrease in the SH content was observed after spontaneous fermentation (C) in 9-month products, whereas LAB tests showed an increased SH content. This increase in the SH content in LAB-inoculated samples might be due to the stretching and unfolding of protein molecules, as a result of which new (previously unidentified) internal SH groups were exposed. Previously, most of the reactive/free SH groups in native proteins were masked from the attack by Ellman factors as they were located in hard-to-reach regions of the polypeptide chain [50]. As the conformational structure of the protein changed over time, the unmasking and activation of SH groups occurred, and they could be detected according to the Ellman reaction protocol. It should be emphasized that in 9-month-old products, the HS index for LAB tests was significantly lower (\(p<0.05\)) than in C, which may indicate limited protein oxidation in these meat products. This study confirmed the relationship between fat oxidation (based on TBARS) and oxidation of myoglobin--as a protein representative (based on Oxi)--as shown in Figure 3. Indeed, HCA showed that TBARS, Oxi, and SH were correlated among themselves, although the interaction of mechanisms in BB12 samples was not as interdependent as in other samples. However, the collinear relationship between fat oxidation (TBARS) and Oxi was strongly significant (\(p<0.05\)) in the BAUER test (Table 4). Indeed, samples fermented by the _L. acidophilus_ Bauer L0938 strain showed a lower (though not the lowest among the LAB variants) TBARS index and a higher Oxi (indicating a lower level of myoglobin oxidation) during aging. Moreover, a strong linear correlation between Oxi and indicators of other parameters reflecting the degree of protein oxidation was observed in BAUER samples (HS and SH). Comparing this finding with the observations described above, it can be concluded that the increase in oxidative changes within proteins (HS and SH) is accompanied by a decrease in the TBARS content in the BAUER test, which may indicate that the intensity of oxidative processes in meat products is dependent on the presence of this LAB strain. Conceptualization, J.S. and P.K. ; methodology, P.K. ; validation, P.K., P.G. and L.S. ; formal analysis, P.K. ; investigation, P.K., P.G. and L.S. ; data curation, P.G. and L.S. ; writing--original draft preparation, P.K. ; writing--review and editing, J.S. and D.K.-K.; visualization, P.K. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Not applicable. Not applicable. Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.