## Results and Discussion
### Colour Measurements and Model Development/Validation of a* Value  
Vivid red colour of ground beef is a primary attribute that consumers set as a key for quality acceptance on purchase. In fact, the presence of any discoloration, or metmyoglobin affects consumer preferences and may result in a total loss to retail stores of over $1 billion dollars annually [40]. Thus, colour evaluation becomes an important factor for the meat industry not only for quality control, but also for the commercialization of a product [6; 41]. Considering the above, colour evaluation was included in the present study by monitoring \(L^{*}\), \(a^{*}\), and \(b^{*}\) parameters on the surface and the bottom of ground beef packaged with or without \"_tsipouro_\". Specifically, \(L^{*}\) values remained unchanged (\(p\geq 0.05\)), while \(b^{*}\) decreased (\(p<0.05\)) during storage, at all temperatures, sampling sides (i.e., top surface or bottom) and treatment (data not shown). Notably, on day 0, the recorded \(a^{*}\) values were lower (24.4-28.6) in ground beef samples treated with \"_tsipouro_\" compared to controls (28.5-32.0), suggesting an acute effect of the distillate on the red colour of the product (Figure 5). Moreover, samples treated with \"_tsipouro_\" showed greater stability of \(a^{*}\) value during storage compared to controls. The latter observation is also reflected on the estimated \(k_{colour}\) per treatment (\(p<0.05\)) (Table 3). A possible interpretation may be the antioxidant properties of \"_tsipouro_\" due to the presence of phenolic compounds in its composition, combined with the well-known property of high oxygen MAP for maintenance of the myoglobin pigment in its oxygenated form, oxymyoglobin, inhibiting the rapid formation of metmyoglobin, and thus, enhancing red colour [42; 43]. Moreover, the recorded coloured stability in samples packaged with \"_tsipouro_\" was even higher at the bottom of the ground piece compared to surface. This is possible related to the direct contact of the bottom side of meat with \"_tsipouro_\", contrary to the surface, where any antioxidant activity was indirectly conveyed through vapours. Figure 4: Simulated growth curves and observed data of **(I)**_B. thermosplucta_ and **(II)** LAB in ground beef (500 g) packaged (**a**) without (controls) or (**b**) with absorbent pads supplemented with a total volume of 50 mL \"_tsipouro_\" (40 mL under the ground beef piece and 10 mL under the labelling, facing the headspace) under 80% O\({}_{2}\): 20% CO\({}_{2}\) and stored at dynamic temperature conditions. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sampling Side** & **Treatment** & **Temperature (\({}^{\circ}\)C)** & \(K_{colour}\) (day\({}^{\circ}\)-1)** & \(\mathbf{R^{2}}\) \\ \hline \multirow{8}{*}{Surface} & \multirow{4}{*}{Control} & 0 & \(-0.852\pm 0.095\)\({}^{\mathrm{A}}\) & 0.976 \\  & & 4 & \(-1.079\pm 0.028\)\({}^{\mathrm{A}}\) & 0.949 \\  & & 8 & \(-2.060\pm 0.093\)\({}^{\mathrm{B}}\) & 0.937 \\  & & 12 & \(-5.322\pm 0.032\)\({}^{\mathrm{C}}\) & 0.971 \\ \cline{2-5}  & & 0 & \(-0.343\pm 0.004\)\({}^{\mathrm{A}}\) & 0.769 \\  & & 4 & \(-0.737\pm 0.057\)\({}^{\mathrm{A}\mathrm{B}}\)\({}^{\mathrm{A}}\) & 0.961 \\  & \({}^{\prime\prime}\)_\({}^{\prime\prime}\)_ & 8 & \(-0.838\pm 0.047\)\({}^{\mathrm{A}\mathrm{B}}\)\({}^{\mathrm{A}}\) & 0.888 \\  & & 12 & \(-0.953\pm 0.284\)\({}^{\mathrm{B}}\)\({}^{\mathrm{A}}\) & 0.887 \\ \hline \multirow{8}{*}{Bottom} & \multirow{4}{*}{Control} & 0 & \(-0.472\pm 0.074\)\({}^{\mathrm{A}}\) & 0.846 \\  & & 4 & \(-1.027\pm 0.021\)\({}^{\mathrm{A}}\) & 0.972 \\ \cline{1-1}  & & 8 & \(-1.039\pm 0.153\)\({}^{\mathrm{A}}\) & 0.869 \\ \cline{1-1} \cline{2-5}  & & 12 & \(-2.966\pm 0.532\)\({}^{\mathrm{B}}\) & 0.906 \\ \hline \multirow{2}{*}{_“Tispouro”_} & \multirow{2}{*}{4} & 0 & \(-0.242\pm 0.031\)\({}^{\mathrm  
Thus, \(a^{*}\) which corresponds to red colour, was selected as the critical one for modelling purposes among the three parameters.