Evaluation of the rheological properties of myofibrillar proteins from different beef muscles is important in meat processing. These properties can affect consistency as well as handling of the comminuted meat products (Xiong and Blanchard, 1994). The rheological behavior or flow of "tacky" salt soluble extracts is often expressed by measuring viscosity. Viscosity has also been used to determine the degree of fish and duck myofibrillar proteins denaturation and aggregation during frozen storage (Jimenez-Colmenero, and Borderias, 1983; Lesiów, 1994) which is hypothesized to be related to changes in actomyosin (Borderias, et al., 1985). In a number of recent investigations conducted mainly on poultry myofibrillar proteins, viscosity has been evaluated and compared in relation to the following factors: protein concentration, ionic strength, pH, shear rate, time of storage, temperature and type of ions in solution. Increase in protein concentration and a raise in pH increased viscosity of actomyosin from chicken breast, pork Ld and hacke muscles (Cofrades et al., 1993) and salt soluble proteins (SSP) from white and red chicken muscles (Xiong and Blanchard, 1994). Viscosity decreased with higher ionic strength in both chicken and hacke actomyosin according to Cofrades et al. (1993) and this was possibly due to the fact that an increase in salt concentration was accompanied by an increase in number of actomyosin monomers, so that the molecules were smaller which resulted in smaller viscosity values. Depending on pH and ionic strength myosin molecules have different arrangements. At low ionic strength and neutral pH myosin molecules are packed as filaments but at ionic strength greater than 0.3, myosin molecules dissociate and disperse as monomers (Cofrades et al., 1993). Lesiów (1997) reported that chicken breast homogenate at pH 6.3 exhibited greater viscosity than chicken thigh homogenate at pH 6.6. Moreover, breast homogenate prepared at 48 hours p.m. and thigh homogenate after 48 and 72 hours p.m. had greater viscosity when homogenates prepared from both type of muscles after 24 hours p.m. The Sm and Ld muscle tissue functional properties during aging were published in recent papers (Lesiów and Ockerman,1998a,b) but the viscosity of the homogenates from Sm and Ld muscles were presented in only one of the twelve possible shear rate values.
The objective of this study was to examine under different shear rate apparent viscosity of homogenates prepared from Sm and Ld muscles cut 24 hours p.m. and additionally aged up to 96 hours p.m.