# Is Prolonged Ageing a Necessity for Improving the Quality of Sous-Vide Cooked Beef?
## 1 Introduction
Moreover, at temperatures of 55-60 \({}^{\circ}\)C, the activity of proteolytic enzymes that degrade myofibrillar proteins including calpain, cathepsin B and cathepsin L is partially maintained [19]. There are also changes in connective tissue related to the action of the collagenase [20]. Bearing in mind all the changes occurring during the heating of meat, in the present study, sous-vide cooking was conducted at 60 \({}^{\circ}\)C. As a result of sous-vide cooking, changes in meat microstructure occur. As shown by [PERSON] et al. [21], sous-vide cooking proceeded at 60 \({}^{\circ}\)C increased the percentage of space between muscle fibres compared with uncooked or boiled beef. This increase resulted from a reduction in the diameter and cross-sectional area of muscle fibres and gradual dissolution of the collagen being part of the intramuscular connective tissue, and was accompanied by a reduction in shear force compared to boiled beef. In the study, the sous-vide cooking of beef steaks from _longissimus humporum_ was proceeded at 60 \({}^{\circ}\)C for 4 h. This combination of a sous-vide time and temperature falls within the range indicated in many culinary guidelines, such as the Culinary Pro website [22], and ensures a pasteurisation effect [13]. [PERSON] et al. [23] reported that beef steaks sous-vide processed at a similar temperature to that used in the study (62.5 \({}^{\circ}\)C) just after 120 min of cooking met the standards specified for this kind of product (a reduction in bacterial counts for more than five log cycles). Sous-vide cooking at 60 \({}^{\circ}\)C produces lower cooking losses in meat than higher temperatures (i.e., 70 \({}^{\circ}\)C and 80 \({}^{\circ}\)C) [24]. Increasing the processing time also leads to increased cooking loss [24], which in turn might decrease products' juiciness [25]. Therefore, a proposed combination reflected issues associated with food safety, tenderness development, cooking loss and the juiciness of products. The sous-vide temperature and time combination (60 \({}^{\circ}\)C 4 h) was also used in our earlier studies [26; 27; 28]. In a preliminary study, the microbial safety of meat products after sous-vide cooking at 60 \({}^{\circ}\)C for 4 h was confirmed (not published data, total viable counts 2 log\({}_{10}\) cfu/g, psychrotrophs 1 log\({}_{10}\) cfu/g, _Salmonella_ sp. and _L. monocytogenes_ were not detected in 25 g of meat samples). In many countries, including Poland, Hungary, Czech Republic, Germany and Austria, where the proportion of beef breeds is low [29], beef is produced from dairy breeds. In dairy herds, male cattle offspring are sold to beef producers for further fattening. It is estimatedthat in Poland, over 50% of beef is produced from young dairy (mainly Holstein-Friesian) bulls [30]. Therefore, beef obtained from young Holstein-Friesian bulls was used in the study. Our previous study showed that prolonging the ageing time of _longissimus lumborum_ muscle obtained from Polish Holstein-Friesian young bulls from 9 to 14 days did not affect tenderness and shear force after sous-vide cooking [26]. However, no information is available on the tenderness of beef sous-vide cooked products obtained from Holstein-Friesian beef aged for wider periods. Based on the assumption that sous-vide cooking enables obtaining tender meat products even from tough meat pieces [14; 15] and the fact that ageing meat before its placing on the market requires time and energy, the hypothesis was set that the ageing time of beef subjected to sous-vide cooking might be shortened to 4 days with no quality deterioration. Therefore, in the present study, the quality of sous-vide cooked _longissimus lumborum_ muscle after 4, 14 and 21 days of wet ageing was determined.