A total of 376 distinct protein spots were visualised and 89 were identified by mass spectrometry. They were used to build a 2DE database which is available as Porcine Database in the University College Dublin 2D PAGE database. Most of the proteins fell into one of three groups representing structural proteins, stress response proteins or metabolic enzymes and many were found in several spots, showing that isoforms must be present.
Some interesting proteins were detected within this large group. For instance, breakdown products of myofibril structural proteins that have previously been linked to meat tenderness were detected, so they might be useful as biomarkers of pork tenderness. Peroxiredoxin, a second protein associated with tenderness, was also identified.
Within these proteins, the abundances of 20 were found to vary significantly between the three phenotypes. The changes were visualised by principal components analysis which showed clear clustering of the phenotypes using two principal components.
When the high and low drip loss phenotypes were compared, triosephosphate isomerase, creatinine kinase M-type, serum albumin and transferrin were less abundant in the high group, while β-tropomyosin was more abundant.
Three stress-related proteins were also found to be differentially expressed. One of them, stress-induced phosphoprotein, was less abundant in the high and low drip loss samples than in the intermediate one, the first time that an association with WHC has been reported.
Some myofibrillar proteins also varied in abundance between phenotypes, including titin, tropomyosin α-1 chain and β-tropomyosin. Their changes indicate rapid degradation of the cell structure following animal death.
Although this is a preliminary investigation into the WHC of pork, the results will help to decipher the molecular mechanisms involved while the new protein database will be useful for other researchers in this area. In the long-term, it may be possible to control drip loss and maintain the yields of pork meat during storage.
The samples were run again by 2D PAGE but this time on preparative gels and the protein spots were cut out for analysis by mass spectrometry. MALDI MS and MS/MS were carried out in the first instance and the peptide masses were searched against a porcine database. When spots could not be identified this way, the proteins were reanalysed by LC-tandem-MS.