Influence of ultimate pH on bovine meat tenderness during ageing.

The aim of this work was to evaluate the influence of ultimate pH and ageing at 2±2°C on the tenderness of beef. The m.longissimus thoracis et lumborum from 23 young bulls excised at 28 h post mortem were grouped into: Normal (pH 5.5 to 5.8) moderate DFD (mod DFD) (5.8<pH<6.2) and DFD (pH 6.2 to 6.7). The toughness as measured by Warner-Bratzler shear force (WBSF) and sensory evaluation, was significantly (p<0.05) lower in the DFD group than in the Normal one and a significant (p<0.001) linear relationship was found between ultimate pH and tenderness as evaluated by both methods. The myofibrillar protein solubility (MPS) at pH 7.0 was significantly higher in the DFD group at all post mortem times whereas for myofibrillar fragmentation index (MFI) higher values (p<0.05) were only found in the DFD group at day 1. In all three groups toughness decreased (p<0.05) from 1 to 6 days, with no further decrease to 13 days. This decrease in toughness was associated with an increase of MFI in all pH groups. Collagen solubility in all three groups was not affected by ageing. No significant (p>0.05) differences in soluble collagen and myofibrillar protein solubility (MPS) at pH 5.5 were found between the pH groups at any time. The tenderness evaluated by both methods was significantly (p<0.05) related to MFI, MPS at pH 7.0, cooking loss and juiciness. Total and soluble collagen, sarcomere length, intramuscular fat and MPS at pH 5.5 were not significantly (p>0.05) related with tenderness.