Technical Abstract: The objective of this study was to determine the effects of hydrodynamic pressure processing (HDP) and postmortem aging on the sarcoplasmic protein fraction of beef strip loins. Loins (n=12) were halved at 48 h postmortem and assigned to HDP or control treatments. Following treatment, each half was divided into three portions which were aged for 0, 5, and 8 days. Sarcoplasmic protein fractions of the muscle samples were isolated and analyzed by capillary electrophoresis (CE) and reversed-phase high performance liquid chromatography (RP-HPLC) to detect differences in protein profiles. Significant HDP by aging interactions were not detected within the sarcoplasmic muscle fractions using either separation technique. With CE analysis, no significant HDP effects were observed but eight peaks corresponding to proteins ranging in size from 17 to >200 kDa were influenced by postmortem aging. Chromatograms from RP-HPLC separation of sarcoplasmic fractions showed that HDP influence the relative size of two protein peaks while nine peaks were influenced by postmortem aging. Various changes in the sarcoplasmic protein fraction detected by both CE and RP-HPLC were significantly correlated to Warner-Bratzler shear force measurements. Overall, data demonstrates that HDP and aging have additive effects on sarcoplasmic proteins and suggest that changes in sarcoplasmic protein profiles may be useful indicators of tenderness.