## 1 Introduction
Despite the attractive presentation of meat in MAP, especially in the first week of exposure, this packaging method has certain limitations. High O\({}_{2}\) concentration promotes the development of undesirable quality defects, such as the growth of microbiota, increased storage leakage, lipid oxidation, discolouration, loss of nutrients, and changes in meat texture [3; 5; 13; 14; 15; 17; 18]. Therefore, various studies are conducted to mitigate adverse changes. Globally, researchers have explored variable proportions of gasses in packaging, looking for a universal mixture that can maintain the broadly understood quality of fresh meat at the highest level, but these researchers have encountered various obstacles [7; 19; 20; 21; 22]. The main problem indicated in studies was the accelerated process of protein oxidation, which is associated with increased weight loss during storage. Moreover, the gas mixtures used did not show any additional antimicrobial effect, and the results indicated that optimization of the oxygen concentration in the modified atmosphere (MA) is necessary when packaging various retail types of meat to significantly improve their oxidative stability [23; 24; 25]. The possibility of using MAP (30% O\({}_{2}\)/70% N\({}_{2}\) and 10% O\({}_{2}\)/90% N\({}_{2}\)) combined with lowering the storage temperature to \(-3\)\({}^{\circ}\)C was also investigated. However, the limitation of the method proposed was the need to maintain a lower cooling temperature than usually used in home refrigerators [26]. Also, the use of antimicrobial chitosan coating in combination with MAP (20% CO\({}_{2}\) and 80% O\({}_{2}\)) did not provide the expected results due to the increased effect of protein peroxidation [27]. [PERSON] et al. [28] tested the possibility of using MAP with foil containing silver ions due to their commonly known antibacterial properties. However, their research results eliminated the use of a nanosilver coating to extend the shelf life of meat, due to the small impact of the addition of silver on myoglobin forms in the first days of storage and an ineffective attempt to limit the growth of dangerous microflora. Our previous research was an attempt to solve the problem of unfavourable changes in pork meat colour signalled by the meat industry by surface application of oregano essential oil [3]. The study showed that the surface application of the essential oil allows for obtaining sensory-attractive products, but does not limit changes in the colour of meat during storage. The colour of meat might be also associated with the husbandry system. Recent proteomic studies suggest that the type of chicken husbandry system (organic versus antibiotic-free) affected the proteome of chicken breast muscle after slaughter, which consequently modified meat quality [29]. Furthermore, an increased abundance of proteins associated with animal growth processes, such as \(\alpha\)-actin isoforms (ACTA 1) and myosin isoforms (MYH 2), was observed in meat from the antibiotic-free group [29]. [PERSON] et al. [30] indicated that the presence of MYH2 contributed to an increase in muscle mass in pigs. The presence of this fibre types affects many aspects of meat quality, including colour, WHC, tenderness, juiciness, and flavour [31]. The fact that the elimination of antibiotics from animal feeding might affect the quality of meat so deeply, and the lack of studies conducted on antibiotic-free pork loin in terms of colour changes during MAP storage, were drivers for designing our study. Moreover, despite some previous studies on the influence of MAP on meat quality, our experiment was designed to investigate the possibility of solving a particular industrial problem associated with unfavourable colour changes in antibiotic-free pork during storage. Therefore the study is innovative due to its individualised nature, but it also has a practical dimension.