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

[Display omitted] • Beef steaks were divided into three groups according to ultimate pH (pHu): N, I, H. • IpHu and HpHu group showed the highest and lowest shear force. • The earlier activation of caspase 9 contributed on the better tenderness of HpHu beef. • Nine differential phosphorylated peptides were detected to link with pH u and WBSF. • Phosphorylation of glycogen synthase may cause the delay of tenderization of IpHu beef. This study investigated the relationship between tenderness and protein phosphorylation levels of normal ultimate pH (pH u , 5.4–5.8, NpH u), 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 NpH u 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. [ABSTRACT FROM AUTHOR]