# Is Prolonged Ageing a Necessity for Improving the Quality of Sous-Vide Cooked Beef?
## 3 Results and Discussion
### The Influence of Ageing on Sous-Vide Cooked Beef  
Sous-vide cooking changed the colour of beef (Tables 2 and 3). The colour of the surface of sous-vide steaks, regardless of the ageing time, was darker, less red and less yellow compared to the cross-section colour, which results in less saturated and vivid (lower chroma) colour (Table 3). The colour of cooked meat, described as dull brown, has been associated with heat-induced myoglobin denaturation ([PERSON] et al., 2018). Myoglobin denaturation starts around 55-65 \({}^{\circ}\)C ([PERSON] et al., 2018); therefore, it occurs at the temperature of 60 \({}^{\circ}\)C, which was used in the present study in sous-vide cooking. According to [PERSON] et al. ([PERSON] et al., 2018), heat treatment during cooking induces a non-uniform distribution of protein denaturation in macro meat systems, which might explain the differences in colour between the surface and cross-section area. Moreover, the outer surface of sous-vide cooked products was subjected to longer contact with the temperature of 60 \({}^{\circ}\)C, which provoked more intense myoglobin denaturation. Moreover, there is a strong relationship between the chemistry of myoglobin (its redox form) in uncooked meat and cooked products, which affects the colour of cooked meat ([PERSON] et al., 2018). The thermal stability of myoglobin depends on its redox state--deoxymyoglobin is more resistant to heat-induced denaturation than oxymyoglobin, whereas oxymyoglobin is more resistant than metmyoglobin ([PERSON] et al., 2018). Probably, on the outer surface of beef steaks, there was a higher proportion of less resistance to heat-induced denaturation myoglobin forms (oxymyoglobin and metmyoglobin) than in the centre of beef steaks. \begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**Attribute**} & \multicolumn{4}{c}{**Ageing Time (days)**} & \multirow{2}{*}{**Significance**} \\ \cline{2-2} \cline{4-4}  & **4** & **14** & **21** & \\ \hline Surface colour & & & & \\ \(L^{*}\) & 32.7 \({}^{\text{b}}\)\(\pm\) 0.6 & 32.3 \({}^{\text{b}}\)\(\pm\) 0.4 & 35.2 \({}^{\text{a}}\)\(\pm\) 0.5 & * \\ \(a^{*}\) & 8.22 \(\pm\) 0.23 & 7.40 \(\pm\) 0.17 & 7.84 \(\pm\) 0.21 & NS \\ \(b^{*}\) & 6.69 \({}^{\text{ab}}\)\(\pm\) 0.16 & 6.37 \({}^{\text{b}}\)\(\pm\) 0.11 & 7.05 \({}^{\text{a}}\)\(\pm\) 0.12 & * \\ \(C^{*}\) & 10.68 \(\pm\) 0.27 & 9.84 \(\pm\) 0.22 & 10.65 \(\pm\) 0.18 & NS \\ \(h^{\circ}\) & 39.1 \({}^{\text{b}}\)\(\pm\) 0.7 & 40.6 \({}^{\text{ab}}\)\(\pm\) 0.6 & 41.9 \({}^{\text{a}}\)\(\pm\) 1.0 & * \\ Cross-section colour & & & & \\ \(L^{*}\) & 49.0 \(\pm\) 0.7 & 48.8 \(\pm\) 0.6 & 49.4 \(\pm\) 0.6 & NS \\ \(a^{*}\) & 18.4 \({}^{\text{a}}\)\(\pm\) 0.4 & 16.6 \({}^{\text{b}}\)\(\pm\) 0.3 & 16.1 \({}^{\text{b}}\)\(\pm\) 0.3 & *** \\ \(b^{*}\) & 8.4 \({}^{\text{a}}\)\(\pm\) 0.1 & 7.73 \({}^{\text{b}}\)\(\pm\) 0.12 & 7.90 \({}^{\text{b}}\)\(\pm\) 0.08 & ** \\ \(C^{*}\) & 20.2 \({}^{\text{a}}\)\(\pm\) 0.4 & 18.3 \({}^{\text{b}}\)\(\pm\) 0.3 & 17.98 \({}^{\text{b}}\)\(\pm\) 0.29 & *** \\ \(h^{\circ}\) & 24.8 \(\pm\) 0.5 & 25.1 \(\pm\) 0.4 & 26.2 \(\pm\) 0.4 & NS \\ \hline \hline \end{tabular} Data are presented as the mean \(\pm\) standard error of the mean (SEM). \({}^{\text{ab}}\) mean values in rows with different letters differ significantly at \(p\) < 0.05; NS—non-significant differences (\(p\) > 0.05), * differences significant at \(p\) < 0.05; ** differences significant at \(p\) < 0.01; *** differences significant at \(p\) < 0.001; \(L^{*}\)—lightness, \(a^{*}\)—redness, \(b^{*}\)—yellowness, \(C^{*}\)—chroma, \(h^{\circ}\)—hue angle.  
\end{table} 
Table 3: The effect of wet ageing on the colour of sous-vide cooked _longissimus lumborum_ steaks. After the sous-vide cooking process, significant differences in the colour of the surface and cross-section area of the beef steaks subjected to different ageing times were recorded (Table 3, Figure 1). The surface of the samples aged for 4 days showed lower \(L^{*}\) and \(h^{\circ}\) values when compared with that of samples aged for 21 days (\(p<0.05\)).