The role of ionic strength in the postmortem tenderization of meat

Typescript (photocopy).To investigate the role of ionic strength in the postmortem tenderization of meat, myofibrils from bovine longissimus muscle at 2 hr postmortem were incubated in 0.1 to 0.35M ionic strength buffers under various conditions. Increasing ionic strength or increasing incubation time increased myofibrillar dissociation, and decreased the turbidity of the samples. The dissociation of M-protein, C-protein, actin, tropomyosin and/or paratropomyosin, and myosin light chain-1 from myofibrils increased as ionic strength increased. Lactate (sodium salt) was less effective in dissociating myofibrils than KCl or NaCl. Low pH was also less effective, but the dissociation pattern was different from that caused by elevated ionic strength, as indicated by gel electrophoresis. Samples incubated at pH 5.5 appeared to have more dissociation of a-actin in and tropomyosin/paratropomyosin, while samples incubated at pH 7.0 appeared to have more dissociation of M-protein and actin. Electron micrographs of control samples indicated wide variations in dissociation even with the same ionic strength treatment. In most cases, the Z-line remained intact and the M -line had disappeared. The area corresponding to the C-protein location on the thick filament appeared to be more resistant to dissociation and left two distinct lines parallel to the Z-line. Trypsin incubation of glycerinated myofibrils markedly increased myofibrillar dissociation, and this dissociation was synergistic with that caused by ionic strength. With 10 min trypsin incubation, myofibrillar structures were still apparent at 0.10M ionic strength, but were no longer identifiable at 0.30M. It is concluded from these data that ionic strength is one of the mechanisms responsible for the postmortem tenderization of meat. In pre-rigor muscle, the high ionic strength and low pH caused by electrical stimulation could reduce the amount or strength of rigor bond formation. During conditioning, the high ionic strength would cause the resolution of actomyosin and weaken the structural integrity of muscle