Other researchers have also reported the effect of fat tissue on tenderness: adipose tissue deposits in the longissimus muscle appeared to disrupt the structure of intramuscular connective
tissue (Nishimura et al. 1999) and matrix metalloproteinases (MMP), while the expression increased during adipocyte differentiation (Bouloumie et al. 2001), improving meat tenderness (Phillips et al. 2000).These reports suggest that meat tenderness was affected by not only the chemical composition but also by protease activity, resulting in piecewise linear regression that was difficult to identify, as shown in Fig. 5. In the present study the SFV decreased when the fat level increased (Fig. 5), although there was little change in the protein content in beef containing fat