Contribution of Early-Postmortem Proteome and Metabolome to Ultimate pH and Pork Quality

This study's objectives were to identify how subtle differences in ultimate pH relate to differences in pork quality and to understand how early-postmortem glycolysis contributes to variation in ultimate pH. The hypothesis was that elements in early-postmortem longissimus thoracis et lumborum proteome and metabolome could be used to predict quality defects associated with pH decline. Temperature and pH of the longissimus thoracis et lumborum were measured at 45 min, 24 h, and 14 d postmortem. Quality measurements were made after 14 d of aging. Groups were classified as normal pH (NpH; x̄ = 5 . 59 [5.53–5.67]; NpH, n = 10) and low pH (LpH; x̄ = 5 . 42 [5.38–5.45]; LpH, n = 10) at 14 d postmortem. Metabolites from 45 min postmortem were identified using GC-MS. Relative differences between proteins were quantified with two-dimensional difference in gel electrophoreses, and spots were identified with MALDI-MS. Western blot analyses were used to measure phosphofructokinase, peroxiredoxin-2, and reduced and non-reduced adenosine monophosphate deaminase-2 at 45 min and 14 d postmortem. Ultimate pH classification did not affect 45-min-postmortem pH (P = 0.64); 14-d pH was different between groups (P < 0.01). NpH had less purge loss (P < 0.01), was darker (P < 0.01), had lower star probe (P < 0.01), and had less intact day-7 desmin (P = 0.02). More pyruvate (P = 0.01) and less lactate (P = 0.09) was observed in NpH, along with more soluble lactate dehydrogenase (P = 0.03) and pyruvate kinase (P < 0.10). These observations indicate that differences in enzyme abundance or solubility may produce more pyruvate and less lactate. Fructose 6-phosphate was more abundant (P = 0.08) in the LpH group, indicating that phosphofructokinase may be involved in glycolytic differences. Furthermore, greater abundance of heat shock proteins, peroxiredoxin-2 (P = 0.02), and malate (P = 0.01) early postmortem all suggest differences in mitochondrial function and oxidative stability that contribute to quality differences. These results show that even subtle changes in ultimate pH can influence pork quality. The proteome and metabolome at 45 min postmortem are associated with variation in the extent of pH decline.