Changes in meat quality characteristics of two beef muscles during ageing

During the ageing period, meat organoleptic properties change, in particular tenderness due to proteolytic and derivative processes. The aim of this study was to evaluate the development of this qualitative parameter in beef during the first 10 days post-mortem in two different muscles (longissimus thoracis -LT and semitendinosusST) of 8 young bulls. Shear force in cooked meat was higher in ST than in LT and decreased during ageing for both muscles (from 101.9 N to 64.2 N for ST and from 89.4 N to 52.7 N for LT). However raw meat shear force showed a rapid fall at 2 days, particularly for LT muscle, successively increasing and decreasing again after 5 days to reach the minimum value the tenth day. While insoluble collagen content showed the maximum value during the second day post mortem (4.5 mg/g for ST and 3.2 mg/g for LT). Thanks to Partial Least Squares multivariate analysis it was possible to estimate the correlation between the first derivative deformation curves of shear force and insoluble collagen. Introduction Tenderness is the most important factor related to consumers' acceptability of meat, and it is known to improve during post-mortem storage. This improvement has been found to be influenced principally by the connective tissue and by the proteolysis of key myobrillar proteins and other associated proteins (Koohmaraie 2006). Both factors, myofibrillar degradation and connective tissue properties, have been reported to be highly influenced by the length of the ageing period (Palke, 2003) and by the studied muscle (Strandine et al., 1949). Therefore the aim of the present work was to determine tenderness changes during ageing period, testing miofibrillar degradation and intramuscular connective tissue properties of two muscles (longissimus thoracis and semitendinosus) by analyzing collagen content and its thermal stability. Materials and methods The longissimus thoracis (LT) and semitendinosus (ST) muscles were studied in eight 18 month-old bulls. As reported by González et al. (2008), both muscles were removed from carcass 3 h after slaughter and subdivided in portions to analyze physiochemical characteristics at different ageing times (1, 2, 5, 8, 10 days). Total (Kolar, 1990) and insoluble collagen (Hill, 1966), expressed as percentage of total collagen, and myofibrillar fragmentation index (MFI) (Culler et al., 1978) were determined on freezing meat. For each ageing time a slide of fresh meat was used to perform shear force on raw meat. Another one was cooked in plastic bag, immersed in a water bath at 80°C until it reached an internal temperature of 75°C and cooled in fresh water for one hour to obtain shear force in cooked meat (Christall et al., 1994). WarnerBrätzler shear force (WBS) on raw and cooked meat was determined in four 1 x 1cm cross section strips using an INSTRON 5543 texturometer. A 50-kg compression load cell and a crosshead speed of 100 mm/min were used. Force-deformation curves from the Warner-Brätzler shear device were obtained on cooked meat by steps of 0.5 mm. From the curves only 85 central data were analyzed (Figure 1) and transformed in first derivative, calculated with the Savitzky-Golay derivative function (Figure 2), to accentuate the curve oscillations depending of variability in myofibrillar structure.