The Sm and the Ld muscles cut at 24 hours p.m. which had ultimate pH lower than 5.8 and pH higher than 6.2 were treated as normal and as abnormally high pH meat, respectively. The relationship between viscosity (Pa.'s) of the Sm and Ld muscle homogenates and shear rate (kxDr)n-1 for various pH groups (pH < 5.8 and pH > 6.2), matched perfectly the Ostwald and Waele equation : eta= kx(Dr)n-1, where k and n values, presented in Table 1, are parameters determined experimentally.
All meat homogenates exhibited pseudoplastic flow (s-1). There was no influence of aging time and type of muscle on the parameter n value (Table 1). Viscosity of SmpH>6.2 and LdpH>6.2 muscle homogenates increased with aging, reaching a maximum after 72 hours p.m. and then insignificantly decreased. The same increasing trend, but during the total aging time, was observed for homogenates from LdpH<5.8, however, after 72 and 96 hours p.m. viscosity values were not significantly different. Aging up to 96 hours had no influence on viscosity of SmpH<5.8 muscle homogenate (Table 1). Apparent viscosity of LdpH<5.8 and LdpH>6.2 muscle homogenates after 48 hours p.m. increased significantly when compared with corresponding values after 24 hours p.m. by 31.45% and 28.95%, respectively. In contrast, for SmpH>6.2 significant change in viscosity occurred after 72 hours p.m. by 71.62% and by 34.17% when compared with its value after 24 and 48 hours p.m., respectively. This data partly corresponds with our previous results which suggest that Sm and Ld muscles cut 24 hours p.m. from normal pH should be further processed within 48 hours p.m. (the highest viscosity) and within 72 hours p.m. (insignificant changes in apparent viscosity between 48-96 hours p.m., Table 1). Comparison of viscosity of homogenates from Sm and Ld muscles of different pH indicate that apparent viscosity of SmpH<5.8 was significantly higher than that of SmpH>6.2 after 24 and 48 hours p.m. and viscosity of LdpH<5.8 was significantly higher than that of LdpH>6.2 after 96 hours p.m. Moreover, after 24 and 48 hours p.m. viscosity of SmpH>6.2 muscle homogenate was significantly lower than viscosity of homogenates from the remaining muscles. Likewise, after 96 hours p.m. viscosity of SmpH<5.8 and SmpH>6.2 muscle homogenates was lower than that for Ld muscles of both pH values. Observed differences in apparent viscosity between normal pH Sm and Ld muscle homogenates after 96 h p.m. can be explained by different distribution of specific fiber types in the Sm and Ld muscles (the Sm has significantly more white fibers and less oxidative fibers -red and intermediate, than the Ld muscle (Batjoens, 1991; Hertzman, et al. 1993; Olsson, et al.1994; Solomon, et al. 1986) and more rapid degradation of the myofibrillar structure in the Ld than in the Sm muscle (O'Halloran, et al.,1997) and maybe differences in myofibrillar proteins extractability from both muscles since it is pH dependent (Xiong and Brekke, 1991).