## 4 Discussion
### Colour Changes and Differences
\begin{tabular}{l c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Attributes**} & \multicolumn{3}{c}{**Modified**} & \multicolumn{8}{c}{**Time (T)**} & \multicolumn{8}{c}{_p-Value_} \\ \cline{2-13}  & **LO** & **HO** & **0** & **2** & **5** & **7** & **9** & **12** & **14** & **15** & **A** & **T** & **AxT** \\ \hline pH & 5.48 \(\pm\) & 5.49 \(\pm\) & 5.58 \(\pm\) & 5.45 \(\pm\) & 5.44 \(\pm\) & 5.45 \(\pm\) & 5.45 \(\pm\) & 5.48 \(\pm\) & 5.49 \(\pm\) & 5.53 \(\pm\) & 5.63 \(\pm\) & \multirow{2}{*}{NS} & \multirow{2}{*}{<0.01} & \multirow{2}{*}{NS} \\  & 0.01 & 0.01 & 0.01 & \(\pm\) 0.01 & 0.01 & 0.01 & 0.01 & 0.01 & 0.01 & 0.01 & 0.01 & 0.01 & \\ \hline Free water & 23.8 \(\pm\) & 24.4 \(\pm\) & 22.0 \(\pm\) & 24.7 \(\pm\) & 24.3 \(\pm\) & 23.7 \(\pm\) & 24.5 \(\pm\) & 23.3 \(\pm\) & 24.2 \(\pm\) & 24.2 \(\pm\) & 23.5 \(\pm\) & \multirow{2}{*}{\(\pm\)} & \multirow{2}{*}{NS} & \multirow{2}{*}{<0.05} & \multirow{2}{*}{NS} \\ (\%) & 0.4 & 0.3 & 0.6 & 0.5 & \(\pm\) & 0.5 & 0.6 & \(\pm\) & 0.7 & 0.7 & \(\pm\) & 0.6 & 0.3 & \\ \hline Purge loss & 5.6 \(\pm\) & 5.2 \(\pm\) & - & 2.8 \(\pm\) & 4.7 \(\pm\) & 5.1 \(\pm\) & 5.7 \(\pm\) & 6.5 \(\pm\) & 6.5 \(\pm\) & 6.9 \(\pm\) & 7.4 \(\pm\) & \multirow{2}{*}{NS} & \multirow{2}{*}{<0.05} & \multirow{2}{*}{NS} \\ (\%) & 0.4 & 0.4 & - & 0.2 & 0.3 & 0.2 & \(\pm\) & 0.3 & 0.7 & 0.8 & 0.6 & \\ \hline Cooking loss & 25.9 \(\pm\) & 26.2 \(\pm\) & 22.3 \(\pm\) & 23.7 \(\pm\) & 24.3 \(\pm\) & 23.2 \(\pm\) & 24.8 \(\pm\) & 27.9 \(\pm\) & 30.9 \(\pm\) & 29.8 \(\pm\) & \multirow{2}{*}{NS} & \multirow{2}{*}{<0.01} & \multirow{2}{*}{NS} \\ (\%) & 0.4 & 0.4 & 0.4 & \(\pm\) & 0.3 & 0.3 & 0.3 & 0.2 & 0.5 & 0.5 & 0.7 & \\ \hline \hline \end{tabular}   
due to changes occurring as the meat ages. In addition, the recording of these significant differences may be due to a difference in the activity of enzymes present in the muscle, which are capable of regenerating the pigment and, thus, the pink colour [41]. Also, [PERSON] et al. [23] indicated that the colour changes in meat stored in packages containing more than 25% CO\({}_{2}\) may be due to acidification of the meat surface and denaturation of proteins. They also explained that CO\({}_{2}\) as an agent alone does not affect the oxidation of myoglobin. The observed significant increase in the \(a^{\star}\) parameter, responsible for the red colour, is most likely due to the increased amount of oxygen in the modified packaging atmosphere (LO 55% O\({}_{2}\), HO 75% O\({}_{2}\)), resulting in the oxygenation of myoglobin to oxymyoglobin [38]. This phenomenon was explained by [PERSON] and [PERSON] [42], who indicated that high oxygen content (above 50%) plays a key role in the interrelation of myoglobin and lipid oxidation processes, thus causing visible changes occurring on the meat surface. Myoglobin content and its redox state are responsible for \(a^{\star}\) values, while only the redox state of the pigment affects \(b^{\star}\)[43]. Also, [PERSON] et al. [44] indicated that the formation of reactive secondary lipid oxidation products can affect the redox stability of Mb. This complex interplay of biochemical processes is a key element in understanding the colour changes of meat stored in modified atmosphere packaging. Also, [PERSON] et al. [10] drew attention to the increased redness value (\(a^{\star}\)) in the case of MA-packaged meat compared to the fresh control sample. The \(a^{\star}\) value is particularly important because it is closely related to the redness perceived by the consumer, where a higher \(a^{\star}\) value indicates a brighter red colour [18]. A significant increase in the \(L^{\star}\) parameter throughout the entire storage period in the present study coincides with the results of a study conducted by [PERSON] et al. [18], which revealed that pork packed in MAP is characterized by a lighter appearance than in the case of atmospheric packaging.