RESUMO
One hundred and ten pigs were fed test diets containing 1·1%, 3·3% or 5·5% fishmeal, 10% rape-seed or 15% rape-seed meal. The control diet contained soya-bean meal. From each carcass M. longissimus dorsi, including subcutaneous fat, was taken and analysed for fatty acid composition and intramuscular fat content. Accelerated oxidation test was carried out on fresh samples. Sensory analyses as well as peroxide and aldehyde analyses were carried out after 0, 4, 6 and 9 months of freezer storage. The sensory properties of fresh meat and fat were not affected by any of the feed components tested. After 6 months of freezer storage slightly increased levels of off-flavours were noted with 3% fishmeal or more in the diet. Also, the peroxide value after storage increased at the same fishmeal level. With rape-seed or rape-seed meal in the diet the scores for off-flavours increased only slightly. A much lower storage stability was noted in fat from pigs fed a combination of rape-seed and fishmeal. Extra vitamin E in diets did not increase the storage stability of pork fat. Special attention was paid to the incorporation of dietary polyunsaturated fatty acids (PUFA), especially marine-PUFA, into body fat. It was found that the incorporation of C22:6 was a very good indicator of the amount of fishmeal in the diet.
RESUMO
Post-mortem metabolism was followed by phosphorus-31-NMR in muscle samples obtained from freshly slaughtered pigs and lambs. Resonances for creatine phosphate (CP), ATP, inorganic phosphate (Pi) and sugar phosphates (SP) could be discerned and the intracellular pH could be determined from the spectra. The rates of post-mortem metabolism varied in the following fashion: porcine muscle > ovine muscle > bovine muscle. However, the course of post-mortem metabolism was, in all cases, the same. CP disappeared first and then ATP. Simultaneously, Pi increased, while SP remained relatively constant. The intracellular pH decreased to pH 5·5 in all tissues. In a separate set of experiments the post-mortem metabolism during thawing was studied in bovine muscles that had been frozen immediately after slaughter. Again, the same course of post-mortem metabolism was observed, but the thaw shortening was accompanied by an extremely rapid post-mortem metabolism, which was more than ten times as fast as that measured for fresh bovine muscles. The intracellular pH decreased from 7·2 to 5·5 in 45 min. This rapid metabolism started only after the sample ha reached 0°C. Resonances for metabolites were broadened in frozen muscles due to the limited motions that are allowed within the ice lattice.
RESUMO
Proton and carbon-13 NMR was used to investigate post-mortem metabolism in bovine muscles at 26°C during the first 10h after slaughter. WALTZ-16 decoupling was used to eliminate the proton couplings in the (13)C spectra and the 'jump and return' pulse sequence was used to suppress the water resonance in the (1)H-NMR experiments. With carbon-13 NMR the glycogen breakdown and the lactate development could be followed. This was compared with the lactate, creatine and phosphocreatine development as measured by proton NMR. The intracellular pH was estimated from the chemical shift of the abundant dipeptide, carnosine, as measured in the (1)H- and (13)C-NMR spectra. These were compared with similar measurements obtained earlier using phosphorus-31 NMR. The three independently determined pH profiles were in excellent agreement with one another, as well as with results obtained with the standard iodoacetate extraction method. In the course of these studies we observed that the post-mortem metabolism in cow and heifer was slow and that it took four more hours to complete compared to bull or young bull. After 10 h the pH was 5·9 in bull and 6·1 in cow. Phosphocreatine had completely disappeared after 3·5 h in bull samples while the lactate continued to increase even after 10h. The curves obtained by carbon-13 and proton NMR for the increase in lactate during the first 10 h post mortem were very similar. Moreover, plots for the increase in the lactate level versus the intracellular pH decrease showed a linear relationship, indicating that anaerobic glycolytic activity is the main determining cause for the intracellular pH decrease. Various other parameters, such as the ratio of unsatirated to saturated fatty acid side chains and the presence of amino acids and taurine, could be measured from the in vivo carbon-13 NMR spectra. However, no gross changes occured in any of these parameters during the first 10 h post mortem.
RESUMO
Meat bulls were assigned to three treatment groups-high voltage intermittent electrical stimulation, low voltage electrical stimulation and no stimulation. Both stimulation methods resulted in a significantly more rapid pH fall in the longissimus and adductor muscles during the first 8 h post mortem. Carcass cooling rates were relatively slow, since temperatures of the longissimus and adductor muscles were 15°C, respectively, at 8 h post mortem. Samples of stimulated longissimus, cut at 24h post mortem and vacuum stored at 3°C for 6 days, had a brighter red colour, higher drip and heating loss, lower shear force values and scored better in taste panels, compared with samples from control carcasses. No significant differences were observed between high and low voltage electrical stimulation in quality traits measured. Although the combined result of pH and temperature measurements during the first 8 h post mortem suggest an absence of cold shortening conditions in control carcasses, a lower sarcomere length was found in samples of the longissimus muscle taken from these carcasses at 24 h post mortem.
RESUMO
Phosphorus-31 Nuclear Magnetic Resonance ((31)P-NMR) has been utilized to follow non-invasively the post-mortem metabolism of the major phosphorylated metabolites in muscles from beef slaughter carcasses. In addition to adenosine-5'-triphosphate (ATP), creatine phosphate (CP) and inorganic phosphate (P(i)) considerable amounts of glucose- and fructose-6-phosphate (G6P and F6P, respectively) as well as glycerol-3-phosphate (Glyc3P) were detected. ATP was mainly present as a Mg(2+)-ATP complex. Adenosine-5'-diphosphate (ADP) appeared to be mainly bound to muscle proteins. A good quantitative agreement was found for the levels of ATP, CP and sugar phosphates (SP) when estimated by NMR or enzymatic assays. Since the chemical shifts of the P(i) and sugar phosphate resonances are a function of the pH, the intracellular pH could be directly deduced from the NMR spectra. Values obtained in this manner were, within the errors of both methods, the same as those determined in iodoacetate/KCl homogenates. The pH gradients within the tissue never exceeded 0.3 pH units. In a final set of experiments we used (31)P-NMR 10 study the effects of electrical stimulation on the intracellular pH and post-mortem metabolism. It was concluded that (31)P-NMR, due to its non-invasive nature plus the fact that some of the NMR parameters are sensitive to the intracellular environment, provides a useful complement to existing methods for the study of post-mortem metabolism.
RESUMO
After designing a method of handling cattle so that they reproducibly developed DFD meat, pH and temperature in cattle developing DFD and normal meat, respectively were studied. The influence of low voltage stimulation on both groups was also investigated. Depending on final pH and other characteristics of the meat, the carcasses could be assigned to subgroups representing pronounced DFD, slight DFD and normal meat, with and without electrical stimulation. In normal and in pronounced DFD carcasses electrical stimulation speeded up the pH drop but did not affect the final state of the meat. In stressed animals the pH values are variable for the first few hours post mortem. This effect is enhanced by electrical stimulation which, in carcasses with slight DFD (from stressed but not exhausted animals), may produce extremely fast pH drop and PSE-like meat. There is no evidence that electrical stimulation would influence the incidence of DFD in cattle slaughtered under commercial conditions. In normal animals electrical stimulation raised the carcass temperature during the first few hours post mortem by approximately 2°C. Carcasses from stressed animals had a higher temperature, independent of stimulation.
RESUMO
The physical and sensory properties of meat from sixteen exhausted and sixteen gently treated young bulls were investigated. The influence of electrical stimulation was also studied. The meat was divided into three groups-meat with ultimate pH ≤ 5·80 (normal meat), 5·81-6·19 (medium meat) and ≥6·20 (DFD meat), respectively. DFD meat showed typical DFD properties and had a higher initial tenderness but a smaller increase in tenderness than normal meat during storage. The medium meat was tough and behaved in some ways as DFD meat and in others like normal meat. Lower correlation between shear force measurement and sensory evaluated tenderness was obtained for DFD than for normal meat. The cooking loss of DFD meat was about 10% lower than that of normal and medium meat. No significant correlation could be found between storage loss, cooking loss, frying loss and juiciness. The electrically stimulated meat was-especially for normal meat-more tender and juicy than unstimulated meat. No obvious influence due to electrical stimulation was noticed on colour, cooking loss, frying loss or storage loss. Electrical stimulation of stressed, but not exhausted, animals may produce meat with PSE properties.
