Myofibrillar activityfrom two different musclesof Gentile di Puglia lambs

Different studies suggest that the disparity in functional properties among various muscles or fiber types can be attributed mainly to myofibrillar proteins. The myosinis different in istochemical, biochemical, enzymatic properties and degradation on postmortem storage. Proteolytic enzyme activity participates in myofibrillar breakdown and continues to be active in muscle post-mortem influencing tenderization of meat. Age and type of muscle are two factors which are involved in the proteinases activity. In this study activity of cathepsin D and Warner-­ Bratzler Shear (W.B.S.), were measured in the longissimus lumborum (LL) and in the semimembranosus (SM)muscles of 24 lambs slaughtered in two different ages (70 and 110 days). Samples from each muscle were prepared in the lysing buffer (sodium trate buffer, EDTA and Triton) and pH adjusted to 5. Haemoglobin was used as substrate at the 0.6 and 2.0 final concentrations (in %, w/v). The extraction of cathepsin D was also determined with Lowry method. Cathepsin D activity increased with substrate concentrations, reaching the maximum value in the LL muscle with 2% of haemoglobin (P< 0.01) in sample of animals 70 days old. Values of the specific activity (37.12 vs 23.15 mg of tyrosine/g protein/h t 45° C ) and total activity (mg of tyrosine/g muscle/h at 45 °C) of cathepsin D showed the same trend observed above. These data are confirmed by the rheological (W.B.S.) values of the LL muscle compared to SM (2.21 vs 3.25 kg/cmsq; P<0.01) that correlate the amount of the cathepsin D with tenderization of th meat. Between the two ages the younger lambs showed better, but not significant, results for amount of cathepsin D and for shear values.