Inhibition of protease activity. Part 1. The effect on tenderness and indicators of proteolysis in ovine muscle

To examine the effect of particular enzyme groups on tenderness specific cy steine protease inhibitors were injected into muscle early post-mortem. The protease enzyme inhibitor E-64 was injected into the m. longissimus thorac is et lumborum (LTL) on the right side of 12 lamb carcasses within 15 min o f death and in another 12 carcasses with the protease inhibitor Z-Phe-Ala-C HN2. The left LTL (control) was injected with saline (0.25 M NaCl). To crea te variation in the rate of pH decline alternate carcasses were electricall y stimulated (low voltage). The LTL was divided into cranial and caudal por tions and aged for 1 or 2 days. Muscle samples at 1 day post-mortem were us ed for measurement of osmolality and sarcomere length (n = 48), and others at I and 2 days post-mortem for shear force determination (n = 96). The myo fibrillar fragmentation index (MFI) was determined on samples taken at pH 6 .2 and 1 and 2 days post-mortem (n = 144). Other muscle samples were obtain ed at death, pH 6.2 and 6.0 and then at 1 and 2 days postmortem (n = 215). These samples were used for determination of protein solubility and the con centration of free amino acids. Stimulation caused a faster (P < 0.05) decl ine in pH. There was no effect of stimulation (P > 0.05) on shear force val ues, but injection of inhibitor and ageing both had effects (P < 0.001). Th e inhibitor E-64 prevented any improvement in tenderness with ageing, where as the inhibitor Z-Phe-Ala-CHN2 and the control samples showed a similar ag eing response. In the latter two treatments there was an average reduction of 1 kg in shear between 1 and 2 days post-mortem, whilst the inhibitor E-6 4 maintained shear force on average 2 kg higher than control samples. Injec tion and ageing had an effect on MFI (P < 0.001) and there was an interacti on (P < 0.05) between stimulation and ageing for MFI, such that as stimulat ed muscle aged the rate of change of MFI was greater. There was an interact ion between injection and ageing (P < 0.05) for protein solubility such tha t samples treated with E-64 showed a minimal increase in protein solubility with ageing, whereas in samples treated with Z-Phe-Ala-CHN2 and the contro l samples there was a significant increase. There was also an interaction b etween stimulation and ageing such that between sampling at pH 6.0 and 2 da ys post-mortem, stimulated muscle exhibited greater solubility (P < 0.05). There were no effects (P > 0.05) on the concentration of free amino acids. The evidence indicated that the cysteine proteases were responsible for pos t-mortem proteolysis and tenderisation, in particular the calpains, whereas the cathepsins (B and L) were unlikely to contribute to proteolysis and su bsequent tenderisation in meat. (C) 2001 Elsevier Science Ltd. All rights r eserved.