| Tenderness is the most important beef palatability attribute, and aging is the basic resolution to this problem. To date, however, the mechanism of beef aging is not fully understood. The purpose of this research is to elucidate the mechanism of beef aging and to demonstrate the palatability changes of beef produced by Chinese yellow cattle during postmortem storage.1 Fresh yellow cattle spleen (within 30 min postmortem) was sampled and treated with procedures such as homogenization, ionic exchange, hydrophobic chromatography, molecular sieve etc., in the last step purified μ-calpain, m-calpain and partly purified calpastatin which were verified by way of SDS-PAGE and casein zymography and with specific activity 38.4U/mg, 39.7U/mg and 14.1U/mg respectively were resulted. Research results on some calpain System kinetics showed that, when frozen, calpain System activity declined with storage time extended, calpastatin, however, was far more sensitive to freezing than calpains; The calcium concentrations required for half maximal activity of u-calpain and m-calpain were ca. 50μM and 330μM; To assay calpain activity accurately, reaction time should be within 60 min, and activity less than 0.45. The Km and Vmax of m-calpain and μ-calpain were 3.185mg/ml, 0.015U/min, and μ-calpain 5.320mg/ml, 0.017U/min.2 Based on hypotheses of Calpain System, calcium and Lysosomal cathepsins with respect to beef aging, purified μ-calpain, calpastatin, myofibrils and leupeptin were used in six different reaction mixtures. After being incubated for different periods in mixed salt solution(MSS) formulated on the basis of the postrigor beef muscle composition and at 4℃ ,SDS-PAGE and western blotting were conducted, the results showed that calcium(100μM)had no effects on myofibrils ,while, μ-calpain, when incorporated with calcium, could degrade desmin and troponinT and the products degraded were similar with that of aged beef; Calpastatin was not capable of inhibiting u-calpain activity completely; No degradation occurred for actin in reaction mixture or aged beef at different time postmortem points. These evidences indicated that it is most possible that μ-calpain degrade cytoskeletal proteins when being activated by calcium, and as a result, improved beef tenderness; nevertheless Lysosomal cathepsins contribution to beef tenderness at earlyaging time period is little.3 Three crossbred yellow cattle (Luxix Limusin) were slaughted according to standard slaughting practices, after being chilled for 20 h, samples were acquired from carcasses and were injected (10% of weight) with distilled water(control), 200 Calcium chloride, 200mM EGTA, 200 mM Znic chloride, 0.2mg/ml Leupeptin, 0.2mg/ml Leupeptin plus 1% Triton X-100, and 1% Triton X-100 respectively. The result indicated that exogenous calpains inhibitors, Leuptptin and Znic chloride, slowed beef aging process significantly, and made beef with higher Wamer-Bratzler shear force(WBS), lower Myofibrillar fragmentation index, extended μ-calpain activity and minor ultrastructure changes, on the controy, however, calcium chloride injection greatly shortened beef aging period, and the shear force value of beef injected with calciun chloride and aged for 4 days was not significantly different with that of control aged for 16 days.4 The quality of six major beef cuts (longissimus dorsi, psoas major, semimemb-ranosus, gluteus medius ,triceps brachii and semitendinosus) sampled from three groups of intact bulls finished with different diet level and slaughted according to standard slaughting procedures, was studied. The results showed that different finishing diet level only had slight effects on beef quality indices except for pH value (P<0.05)and the shear force of psoas major, gluteus medius and triceps brachii (P<0.05), beef drip loss and cooking loss were increased (P<0.05),shear force and color score decreased significantly( P<0.05) with the aging time duration extended, and that different primal beef cuts responses to...
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