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 pHu 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 (pHu, 5.4 - 5.8, NpHu), intermediate pHu (5.8 - 6.2, IpHu) and high pHu (≥ 6.2, HpHu) Longissimus lumborum from beef. During 21 d of ageing, the HpHu group had the lowest Warner-Bratzler shear force (WBSF) values, while the IpHu 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 HpHu group were the key reasons for the lower WBSF compared with the NpHu and IpHu groups. The activity of caspase 3 can not explain the tenderness differences between IpHu and HpHu groups, since their activities did not show any difference. At 24 h post-mortem, 17 common differential phosphorylated peptides were detected among pHu groups, of which nine were associated with pHu and WBSF. The higher phosphorylation level of glycogen synthase may have caused the delay of meat tenderization in the IpHu group.