Proteome analysis of the sarcoplasmic fraction of pig semimembranosus muscle: implications on meat color development.

Two-dimensional electrophoresis was used to investigate sarcoplasmic protein expression in pig Semimembranosus muscles sampled 20 min after slaughter. Two groups (light and dark) of 12 animals were selected from 1000 pigs, based on meat L values measured 36 h postmortem. Twenty-two proteins or fragments (p < 0.05) were differentially expressed. Muscles leading to darker meat had a more oxidative metabolism, indicated by more abundant mitochondrial enzymes of the respiratory chain, hemoglobin, and chaperone or regulator proteins (HSP27, alphaB-crystallin, and glucose-regulated protein 58 kDa). Conversely, enzymes of glycolysis were overexpressed in the lighter group. Such samples were also characterized by higher levels of glutathione S-transferase omega, which can activate the RyR calcium channels, and higher levels of cyclophilin D. This protein pattern is likely to have severe implications on postmortem metabolism, namely, acceleration of ATP depletion and pH fall and subsequent enhanced protein denaturation, well-known to induce discoloration.

Characterisation of PSE zones in semimembranosus pig muscle.

Pig semimembranosus muscles, sampled from normal hams or from PSE-zones of defective hams, were analysed by histochemistry and electrophoretic techniques. PSE zones were characterised by a disorganisation of fibre alignment and a significant increase of inter fibre spacing (26.2% vs. 16.9%, p<0.05). Protein solubility was significantly lower in defective muscle (55.4 vs. 91.5mg/g, p<0.001). SDS-PAGE evidenced in such samples a lower abundance of the 97, 40 and 26kDa bands in the sarcoplasmic fraction and a higher abundance of the 97, 58, 34, 31, 15 and 11kDa bands in the myofibrillar fraction. Intensity of the MHC band (200kDa) was lower in PSE zone samples. By 2-D electrophoresis, it was shown that troponin T, MLC 1 and alpha-crystallin were less proteolysed in defective muscles, while creatine kinase fragments were more represented. One form of HSP 27 was absent from PSE zone samples. Overall, meat from PSE-zones and fast pH fall-PSE meat show numerous histological and biochemical similarities, particularly in their protein characteristics.

Proteome changes during pork meat ageing following use of two different pre-slaughter handling procedures.

The influence of postmortem storage time and pre-slaughter conditions (transport the day before slaughter or immediately before slaughter) on proteome changes of pork meat was investigated over a 72 h ageing period. Intensities of 37 spots varied significantly (p<0.05) with ageing time. Changes indicated proteolysis of troponin T, actin, α-crystallin, myokinase, creatine kinase and mitochondrial ATPase, but also of proteins constitutive of the Z-lines, namely cypher proteins and myozenin. Other modifications were the intensity increase of a full-length protein of the sarcoplasmic reticulum, which may be linked to its increased extractibility after membrane disruption, and a gradual shift in pHi towards alkaline values of some forms of myosin light chains (MLC) 2 and 3. The pre-slaughter conditions affected significantly (p<0.05) 8 spots. Mitochondrial ATPase was over-expressed in the group transported immediately before slaughter, also characterised by a faster pH fall, and the shift in pHi of MLC 2 was more pronounced. The pre-slaughter conditions had no significant effect on the above proteolytic events.

A note on the relationships between cured-cooked and dry-cured ham processing yields.

Right and left hams from 353 pigs slaughtered at around 100 kg body weight were processed into cured-cooked hams and dry-cured hams, respectively. Weights and yields at various stages of each process, carcass lean content and fresh meat quality traits were registered. Technological yield of cured-cooked processing (saleable cooked ham weight/defatted-deboned fresh ham weight) was more closely correlated to ultimate pH (r=0.51, p<0.001) than to carcass leanness (r=-0.13, p<0.05) whereas the reverse situation -r=0.15 (p<0.01) and r=-0.62 (p<0.001), respectively--was found for technological yield of dry-cured processing (saleable dry ham weight/trimmed fresh ham weight). The correlation between the two technological yields was significantly positive but of fairly moderate magnitude (r=0.36). The correlation between the overall yields (saleable processed ham weight/entire fresh ham weight) of the two processes revealed to be very close to zero (r=-0.01).