Muscle fiber characteristics and postmortem quality of , and from Chinese Simmental bulls.

Using Chinese Simmental cattle , , and samples, we assessed muscle fiber characteristics and postmortem quality. The type I, IIA, and IIB fiber diameters were greater in and relative to , with , , and having the highest respective percentages of type I, IIB, and IIA fibers. had the highest and values and lowest values at 1- and 6-hr postmortem. had the lowest Warner-Bratzler shear force (WBSF), hardness, and chewiness values. The trends of WBSF, hardness, and chewiness changes decreased with increasing aging time. had higher changes in WBSF than , and the number % type I fibers was correlated negatively with % changes of WBSF. Therefore, muscles with a high proportion of type IIB fibers and a low proportion of type I had lower tenderness and higher tenderization rate. Further research should be done to seek the optimal composition of muscle fiber type in order to improve beef quality, as muscle fiber type has opposite effect of tenderness background and tenderization rate.