# 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
A reduction in \(a^{*}\), \(b^{*}\) and C* values was also noted on the cross-section of the steaks after 14 days (\(p<0.05\)), which indicated that the meat aged for longer periods was less red and yellow. This finding might indicate that myoglobin was more resistant to heat in 4 d aged samples compared to 14 d and 21 d aged samples. It might be explained by differences in the redox status of myoglobin in uncooked meat. As mentioned above, deoxymyoglobin content decreases during ageing [42]. Therefore, it might be assumed that in 4 d aged beef, there was a higher proportion of deoxymyoglobin, which is more resistant to heat-induced denaturation than other myoglobin forms [43], which contributed to the lower denaturation of myoglobin after sous-vide cooking compared with 14 d and 21 d aged beef. Generally, the colour of the heat-treated beef surface might also result from the Maillard reaction, which is associated with brown colour formation. However, in sous-vide cooked meat products, the Maillard reaction and its impact on cooked meat colour is low [45]. Additionally, it should be pointed out that Maillard reaction products being created on the external surfaces of meats during cooking do not affect the colour of the cross-section area of cooked meat [43]. Cooking loss and the textural attributes of the beef steaks are shown in Table 4. The ageing time did not affect cooking loss (\(p>0.05\)), which was also reported in earlier studies [4; 7; 11]. During heating (even at 60 \({}^{\circ}\)C), meat proteins undergo denaturation, which results in shrinkage in the sarcomere length and transverse shrinkage, creating greater gaps between fibres and reducing the ability of the proteins to hold water [17; 46]. Figure 1: The appearance of sous-vide cooked beef steaks produced from _longissimus lumborum_ aged for 4, 14 and 21 days. WBSF decreased along with the ageing time, and the lowest values were noted after 21 days of ageing compared to 14 d and 4 d aged samples (\(p<0.05\)). The results obtained from the TPA test proved a significant improvement in sous-vide beef texture during ageing in terms of hardness, springiness and chewiness. The changes in these texture attributes were specifically noted between 4 and 14 days, except for springiness, which significantly decreased after 21 days compared to 4 days (\(p<0.05\)). The changes in the texture parameters (WBSF and TPA attributes) noted in this study reflect proteolytic changes that occur during meat ageing [18]. Post-mortem proteolysis conducted by the endogenous enzymatic system during the ageing of meat is used widely in the meat industry to improve meat tenderness; however, it is associated with increased production costs [47]. During ageing structural proteins, including the C-protein, M-protein and cytoskeletal proteins such as titin, nebulin, desmin, dystrophin and vinculin, are broken down by endogenous enzymes (calpains), whereas actin and myosin (being the major contractile proteins) are minimally affected (but they might be regarded as tenderisation markers). During long-term ageing, lysosomal enzymes, cathepsin, and other enzyme groups are also involved in tenderisation [18; 48]. During ageing, changes in collagen structure also occur as a result of the degradation of proteoglycans which stabilise the bonds between collagen fibrils, which is demonstrated by increasing the proportion of total soluble collagen and acetic-acid soluble collagen, as well as a decrease in insoluble collagen concentration in cooked meat [49]. The extent of post-mortem proteolysis affects meat tenderness, but it is also independently shaped during the heat treatment of meat [18]. Moreover, these proteolytic changes continue during sous-vide cooking. In the present study, beef tenderisation was achieved by the combined effect of ageing and sous-vide cooking.