A comparative study on the rate and the extent of tenderness in buffalo, beef and yak: preliminary results

The proteolytic fragment appearance is related to the rate and extent of meat tenderness. In this study we report the results of a preliminary screening on muscle exudates and on the toughness of Semitendinosus (ST) muscle of different species (Buffalo BUF, Maremmana MM and Yak ). The exudates originating from four animals for each species have been analyzed for total protein content and drip loss. The shear force data analyzed at 7d from slaughter have been correlated to the rate of proteolysis, while Magnetic Resonance Imaging (MRI) has been used to monitor the ageing from slaughter to 7d post-mortem. Obtained data point out a higher rate and extent of proteolysis for Yak, giving a lower toughness of its meat. MRI data point out a dark spot in the centre of BUF samples and a MM meat anomalous T2 trend. Introduction The loss of proteinic fluid from meat (called drip or exudate) during ageing is an important factor to determine not only the final meat quality but also to understand the mechanism of tenderisation. It is widely studied in pig meat (Savage et al., 1990) and the structural basis of its formation has been overviewed (Offer & Knight, 1988). The appearance of proteolytic fragments in beef exudates is related to meat tenderness (Kolczak et al., 2003). Moreover, drip loss is inversely proportional to the water holding capacity of meat, which depends on the extent of post-mortem myofibrillar shrinkage and the correlative changes in the extracellular compartments (Renou et al., 2003). A novel approach to determine the WHC is based on MRI. (Renou et al., 2003; Ruiz-Cabrera et al., 2004; Herrero et al., 2007). This technique permits spatial resolution of water content and coupled with NMR parameters defines the state of water interaction with other molecules. The aim of this study is to analyze the biochemistry of the exudates of Semitendinosus muscle coming from different animal species (Buffalo, beef and Yak). Our attention has been focused on the biochemical composition of the proteinic fractions obtained from these drip samples. We have also investigated the correlations of these data with the physical ones (water holding capacity and shear force), at 7d ageing and we have monitored the conditioning of Semitendinosus muscles through MRI. Materials and methods At slaughter, ST muscles have been taken from right half carcasses of four Yak bulls (average live weight: 282.7±24.84), four (BUF) buffalo bulls (average live weight: 333.6±30.30) and four beef (MM) Maremmana bulls (average live weight: 501.7±45.49). In the centre of the muscle two slices (2.00 cm height) have been taken, vacuum-sealed and stored at 4°C. In the first one 3 cores have been sampled (2.54 cm in diameter), cut in parallel to the muscle fibres with a hand-held steel cork borer. These cores have been used to carry out the MRI analysis from 1d to 7d of cold storage. After 7d, the second slice has been used to carry out other analyses on raw and cooked meat. The analysed parameters have been: drip loss percentage (DRIP), Warner Bratzler Shear force (WBSF) and drip protein content (PC). The amount of drip has been measured as reported by Savage et al. (1990). Drip soluble protein content has been determined spectrophotometrically by Bradford’s method, at different ageing time, (Bradford, 1976) using the Bio-rad assay kit and bovine IgG as standard and the total amount of protein lost (PL) has been calculated as reported by Savage et al. (1990). WBSF analysis has been performed on cooked meat (in a water-bath to a final internal temperature of 75°C). Four strips (10mmX10mmX20mm) have been cut parallel to the fibre direction, using an Instron universal testing machine (Model no. 5543, Instron Corporation, UK) fitted with a Warner-Bratzler shear attachment. MRI analysis have been recorded by using a Bruker AVANCE spectrometer (Bruker Biospin, Milan, Italy) with the H frequency resonating at 300.13 MHz, equipped with cylindrical birdcage single-tuned nucleus (H) coil probe head with an inner diameter of 60.0 mm. Water signal has been monitored and used for the image reconstruction. Gradient-Echo (GEFI), T1and T2-weighed images have been obtained with standard MRI sequences. All data have been analyzed with analysis of variance (ANOVA) using the PROC GLM procedure in SAS (SAS, 2001). Pearson correlation coefficients have been generated to describe the relationship between WBSF values and PC ones, using the PROC CORR