Consumption of food products with a high level of compounds that are products of fat or protein oxidation is associated with the onset of various diseases. Therefore, this study estimated the level of oxidation in a fermented long-maturing tenderloin inoculated with lactic acid bacteria strains. To estimate the level of fat and protein exposure to oxidative factors, thiobarbituric acid reactive substances (TBARS), oxidation–reduction potential (ORP), oxygenation index (Oxi) as well as surface ydrophobicity (HS) of protein, and the content of free sulfhydryl (SH) groups were used as indicators of oxidation status. To validate the results, changes in the color of the products were determined using instrumental methods. This study confirmed the relationship between fat oxidation (based on TBARS) and oxidation of myoglobin as a protein representative (based on Oxi). Indeed, statistical analysis showed that TBARS, Oxi and SH were correlated with each other and could be used as indicators of oxidation in fermented products. The findings of this study also showed the use of LAB as starter cultures for meat fermentation may have an impact on the level of oxidation; in particular, the BAUER strain showed a protective effect on proteins in the final stages of the production of dry-cured pork loins.