Tenderness is an important quality trait of dry-cured ham for which changes in the solubility and integrity of the muscle structural proteins are considered to be the main mechanisms responsible for the tenderization of hams during dry-curing. Monin et al. (1997) pointed out that the hardness and chewiness of hams increase during the initial stages of processing due to a decrease in protein solubility and water content and subsequently which decreases as proteolysis progresses. However, intense proteolysis can induce textural defects that may reduce the acceptability to consumers. The relationship between excessive proteolysis and defective texture was first reported in Italian dry-cured hams (Parolari et al. 1994, Virgili et al. 1995). However, although pastiness and softness have been related to increased proteolysis measured as amino acid and peptide contents (Parolari et al. 1988, Careri et al. 1993, Virgili et al. 1999), but the proteins implicated have not been identified. The endogenous lysosomal cathepsins of muscle are thought to be the enzymes mainly responsible in this process (Parolari et al. 1988, Schivazappa et al. 2002). However, several factors have been reported to affect proteolysis: genetic type, sex, age, meat pH and processing (salting, temperature and time) (Buscailhon et al. 1994, Arnau et al. 1998, Garcia-Garrido et al. 1999, Tabilo et al. 1999).

Right and left hams from 353 pigs slaughtered at around 100kg 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).

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.

The role of the 20S proteasome proteolytic effects was revisited using an ultrastructural approach with the aim to explain some particular structural changes identified in type I muscles and in high pH meat. In both types of meat, major changes observed after ageing are an increase in the thickness of the Z-line followed by the appearance of an amorphous protein structure spreading out over the I-band. This was followed by a total degradation of this amorphous structure and of the Z-line. Partial transversal fragmentation of the myofibrils within the I-band can also be detected. The data reported clearly demonstrate that the 20S proteasome was able to mimic these sequential structural changes, a feature never obtained with either calpains or cathepsins. It is the first time that a direct implication of this complex in postmortem muscle is postulated.

The review is aimed at presenting the state of current knowledge into the structure of a glycogen molecule as well as its synthesis and degradation during post mortem changes in muscle tissue. Currently-accepted model of the structure of glycogen molecule is that suggested by Whelan [Immonen, 2000; & Poso Puolanne. 2005 ]. It has been demonstrated that the structure of a molecule is very well adjusted to the functioning of glycogen in muscles through strong packing of glucose panicles and that glucose is well available for glycogenolytic enzymes due to strongly branched structure. The review provides results of research ai pigs referring to the analysis of a variety of interactions of factors (mainly genetic ones, as HAL n /RYR T and RN- genes) on the activity of enzymes related with synthesis and degradation of glycogen in muscles. Recent results of research into factors affecting the activity of glycogen debranching enzyme have shown that fast chilling of carcass is likely to limit the occurrence of PSE defect. Another aspect described in the review is the effect of residual glycogen on meat quality, whose occurrence has been reported in both pigs and cattle. It has been shown to lower the yield of meat in cooking, to affect a decrease in protein content of muscle tissue and to influence the sensory quality of meat.

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.

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.

Investigation was carried out on 96 [(Polish Large White × Polish Landrace) × (Duroc × Pietrain)] fatteners. The results concerning the influence CAST × RYR1 genes interaction on some meat quality parametres suggest that incidence of faulty, exudative meat appearing in some stress-resistant fatteners (CC genotype in relation to RYR1 locus) and also normal meat in some stress-sensitive fatteners (TT genotype in relation to RYR1 locus) may be due to simultaneous modifying effect of genotype in relation to CAST gene on post mortem changes in muscle tissue.

Pigs of the same genetic type at the RN and HAL loci, i.e. rn(+)RN(-)/NN were reared in similar conditions of feeding and housing. They were slaughtered in two abattoirs (referred to as A1 and A2) using a mixture of air (30%) and CO(2) (70%), at a rate of 300 pigs per hour per slaughterline. One hundred and thirty-two pigs from 11 farms were slaughtered in A1 using a corusinga restrainer and 127 pigs from 5 farms were slaughtered in A2 with the backloading technique. pH at 40 min, 2.5 h and 24 h after slaughter and colour (L*, a*, b*) at 24 h after slaughter were measured in the semimembranosus muscle. Meat quality of the ham was scored as follows: 1, no PSE-zone; 2, doubtful; 3, PSE-zones in the semimembranosus and sometimes on the internal flexor muscles; 4, PSE-zones in all the flexor muscles. The muscle pH value was higher in A2 than in A1 at 40 min post mortem (P<0.01), but not at 2.5 and 24 h. L* (P<0.001) and b* (P<0.05) were higher in A1 than in A2. There was a remarkable difference in meat quality scores, with 50% of the hams scoring 3 or 4 in A1, vs 13% in A2. Lairage time before slaughter affected (P<0.01) the pH value at 2.5 h (5.69 vs 5.93). The values of pH1 and pH2.5 decreased with increasing the meat quality score. The values of L* and b* increased markedly with the score. The results of the present study indicate that the method of bringing the slaughter pigs to the stunning device affects the frequency and importance of PSE meat in the ham. The automated driving of groups of animals to the stunning machine combined with the backloading of a nacelle, compared to a traditional system driving pigs in single file using electrical goads and a restrainer was beneficial with respect to both meat quality and animal welfare.

This article illustrates the main problems of technological and sensory quality encountered in pork production and processing using examples taken from the French pork industry. It describes how in the recent past genomics has allowed a clear improvement of the mean technological quality of pig meat produced in France, and presumably in many other countries, by helping to reduce or eliminate the most striking defects (pale soft exudative – PSE and acid meats). It gives a list of foreseeable applications of genomics to adapt technological and sensory qualities to the requirements of meat end-users, in order to deal with growing market segmentation. Finally, it is concluded that in the future the difficulty will rest much more in the choice of carcass types to produce than in the implementation of the selection tools needed for their production.

Stress occurring in pigs, before and during slaughter favours destructured meat (Franck et al., 2000, 2002). We supposed that a restraint stress provoked by immobilising hind limbs by links during a few minutes should be sufficient to induce destructured meat lesions. This kind of stress may be divided into a physical component (muscular effort) and an emotional component (fear). In order to study the two components separately we compared the effects of immobilisation by physical links with the effects of immobilization by chemical muscle relaxation. An infusion of succhinylcholine was used to induce leg paralysis without conscience lost. The situation is considered to be emotionaly very painful.

Rabbit triceps brachii muscle was perfused with bovine red cells medium. Changes in phosphorus compounds and intracellular pH were followed using (31)P NMR during 15 min in the perfused muscle and during 50 min in muscle made anoxic by perfusion stop. Potassium levels in perfusate was maintained at 4 mM (normal plasma concentration at rest) during all perfusion in one muscle and at 4 mM for 10 min then 10 mM during 5 min before perfusion stop in the contralateral muscle. The intracellular pH and phosphorylated compounds content remained stable in the perfused muscle whatever the potassium concentration of the perfusate. Five min after perfusion stop a decrease in phosphocreatine (P<0.05) and pH (P<0.01) and an increase in sugar-phosphates (P<0.01) were observed independently of potassium concentration. The lack of effect of increasing circulating potassium indicates that hyperkalemia does not affect, by itself the muscles energetic metabolism.

The Trade Union of turkey in France (CIDEF) and National Institute of Agronomical Research (Research Meat station of INRA) study the turkey breast meat color to predict meat transformation yield and the consumers' acceptability of fresh fillets. They have asked to Cemagref to develop a new tool based on color numerical vision to determine the relevant objective color measurements which could give prediction of the breast transformation yield to minimize economic loss of the production of turkey ham. In this research project we devised a vision system to research and measure turkey breast meat visual features. A color vision system was developed and calibrated to grab color images and segmentation methods were applied to locate tissues of breast and to measure their color. To find efficient aspect variables, the color results were studied, in relation to breast transformation yield and other measurements included meat pH.

This article is aimed to review the research works carried out to date about structurless pig meat by three French organisations, i.e. ENVL and INRA in the Rhone Alpes region (South East), ITP and INRA in the West of France and Pen Ar Lan Company in Brittany. The results from the 3 groups are gathered and compared. It appears that the lesion is of a PSE type, however this syndrome recovers maybe various pathologies with different mechanisms but an identical expression. All genetic types together, the rate of structurless hams is of 10 to 20 % on average, with a strong variation according to slaughter series, season (more structurless meat in Summer); the heaviest and meatiest pigs show more defects, but this trend is not related to the growth rate. The HAL gene is a predisposing factor, but it is not the only one, as marked differences are observed among genetic types and among boars within-genetic type, although the latter observation should be confirmed. Regarding environmental factors, lairage conditions in the abattoir is noticeable, but other factors are probably involved. The biochemical mechanisms underlying the defect of structurless meat probably involve a deficiency in intracellular Ca++ as in PSE meat. Colour measurements appear as interesting indicators of the muscle destructuration. Moreover they have the interest to replace the subjective scoring by an objective and quantitative measure. Research is currently in progress to assess the possibility of using of video image analysis to quantify the intensity of the defect and to sort the hams in industrial conditions.

Biceps brachii muscle was isolated from anaesthetized New Zealand rabbits and perfused for 30 min with bovine red cells, while electrically stimulated at 0.1 Hz, 50 V. Temperature was maintained at 34 (physiological temperature of this muscle), 36 or 38 °C in the first experiment (Exp 1). In the second experiment (Exp 2), temperature was maintained at either 34 or 38 °C and the muscle was perfused with 2 ng/ml adrenaline and 10 ng/ml noradrenaline for 5 min during the perfusion. Whatever the temperature, twitch force decreased (P<0.01) during perfusion indicating muscular fatigue. Total turnover rate of "energy-rich" phosphate was higher at 38 °C than at 34 °C (P<0.05) during the first 30 min after the perfusion was stopped in Exp 1 and tended to be higher between 30 and 60 min (P<0.10) in Exp 2. Catecholamine perfusion had no effect on contraction and on muscle metabolism whatever the temperature. Our results show that an increase in temperature of 4 °C above the physiological temperature decreases the resistance of oxygenated rabbit muscle to fatigue. In anoxic muscle, temperature increase accelerates the turnover of "energy-rich" phosphate compounds, which is known to be detrimental to meat quality.