Effects of different protein phosphorylation levels on the tenderness of different ultimate pH beef

This study investigated the relationship between tenderness and protein phosphorylation levels of normal ultimate pH (pH(u), 5.4-5.8, NpHu), intermediate pH(u) (5.8-6.2, IpH(u)) and high pH(u) (>= 6.2, HpH(u)) Longissimus lumborum from beef. During 21 d of ageing, the HpH(u) group had the lowest Warner-Bratzler shear force (WBSF) values, while the IpH(u) group showed the highest and even after 21 days of ageing still had high levels. In the late stage of the 24 h post-mortem period the faster degradation rate of troponin T and earlier activation of caspase 9 in the HpH(u) group were the key reasons for the lower WBSF compared with the NpHu and IpH(u) groups. The activity of caspase 3 cannot explain the tenderness differences between IpH(u) and HpH(u) groups, since their activities did not show any difference. At 24 h post-mortem, 17 common differential phosphorylated peptides were detected among pH(u) groups, of which nine were associated with pH(u) and WBSF. The higher phosphorylation level of glycogen synthase may have caused the delay of meat tenderization in the IpH(u) group.