Post mortem energy metabolism and pH development in porcine M. longissimus dorsi as affected by two different cooling regimes. A (31)P-NMR spectroscopic study.

(31)P-NMR spectroscopy was carried out on M. longissimus dorsi samples chilled by two different cooling profiles corresponding to commercial batch and tunnel chilling. The half-life of post mortem phosphocreatine (PCr) degradation was found to be significantly less in muscle samples exposed to tunnel chilling (rapid) compared with muscle samples exposed to batch chilling (soft) conditions, while no difference in the post mortem ATP degradation was found. Moreover, the post mortem pH development in the muscle samples differed considerably between the two cooling regimes. A maximum difference of approx. 0.25 pH units between the two cooling profiles was observed around 150 min post mortem. Theoretical calculations of the registered pH difference between rapid and soft chilling of muscle samples revealed that the temperature effect on the buffer capacity of muscle is the major determining factor in the detected difference in intracellular pH between the two cooling profiles, while any contribution from a temperature-induced delayed progress in the lactate formation post mortem seems negligible. Moreover, calculations on the effect of the registered pH difference between rapid and soft chilling of muscle samples resemble a 2.5 times greater denaturation of myosin in samples which were chilled softly compared with samples chilled more rapidly. Finally, the relationship to the functionality of meats from soft and rapid chilled pork carcasses is discussed.

Origin of multiexponential T(2) relaxation in muscle myowater.

To obtain a further understanding of the nature of the multiexponential T(2) relaxation seen in muscle tissue water (myowater), relaxation measurements were carried out on whole, minced, and homogenized pork of three different qualities with regard to water-holding capacity (normal, red soft exudative, and dark firm dry). Whole, minced, and homogenized pork all resulted in multiexponential T(2) relaxation (three components) independently of the quality, even though microscopic studies on homogenized meat revealed considerable disruption of the macroscopic structure. This states that the relaxation behavior in meat cannot be explained by intra-/extracellular compartmentalization of the water as suggested in earlier studies. Subsequent studies of T(2) relaxation in either whole meat, where the structure integrity was changed by the introduction of dimethyl sulfoxide (membrane disruption) or urea (protein denaturation), or minced meat with added NaCl (inter-/intraprotein interactions) lead to the suggestion that in whole meat (i) the fastest relaxation component reflects water tightly associated with macromolecules, (ii) the intermediate relaxation component reflects water located within highly organized protein structures, for example, water in tertiary and/or quaternary protein structures and spatials with high myofibrillar protein densities including actin and myosin filament structures, and (iii) the slowest relaxation component reflects the extra-myofibrillar water containing the sarcoplasmatic protein fraction. Finally, relaxation patterns in heat-set gels of superprecipitated actomyosin and bovine serum albumin similar to that identified in whole meat support the proposed nature of T(2) relaxation in muscle myowater.

Non-invasive investigation of parenchymal liver disease using 31P NMR spectroscopy.

Four 31P NMR spectroscopy parameters were measured non-invasively in the liver of 11 healthy pigs and 9 pigs with CCl4-induced liver disease: (i) absolute molar concentration of phosphorous metabolites; (ii) pH based on the chemical shift of the P(i) peak; (iii) T1 of the peaks in the 31P NMR spectrum; and (iv) changes in ATP, P1 and phosphomonoester after fructose administration. Liver disease was verified by histology and blood chemistry. The concentration of ATP decreased from 3.0(2.8-3.1) to 2.0(2.0-2.4) mM (median and quartiles) when liver disease was induced (p < 0.05). The concentration of phosphodiesters (PDEs) decreased from 14.8(11.4-19.5) to 8.7(7.4-11.6) mM (p < 0.05). pH increased by 0.1 unit. T1 relaxation times for the gamma-, alpha- and beta-ATP peaks increased from 320(249-471) to 577(506-638) ms (p < 0.01), from 765(611-786) to 906(820-1058) ms (p < 0.05) and from 402(327-509) to 579(543-743) ms (p < 0.01), respectively, while T1 for the PDE peak decreased from 2204(1909-2404) to 1758(1502-1894) ms (p < 0.05). In the healthy animals injection of fructose was followed by a reduction of ATP (beta-ATP). In diseased livers this reduction was significantly smaller. In conclusion, it was possible non-invasively to show differences between healthy and diseased livers in all NMR parameters evaluated. This means that 31P NMR spectroscopy may have a potential as a non-invasive diagnostic method for studying liver disease.

Magnetic field shimming by Fourier analysis.

The homogeneity of the magnetic field of an Oxford 85/310HR magnet was optimized with the use of passive shims (i.e., pieces of steel) and room-temperature electronic shims. Both the characteristics of the passive shims and the current settings for the room-temperature electronic shims were calculated with the goal of minimizing field inhomogeneities as assessed by Fourier analysis of data from circular field plots. The measurement techniques, the methods of data analysis, and the techniques employed in correcting the magnetic field are presented. Difficulties and constructive approaches are suggested in these descriptions. The final results show a field of excellent homogeneity over a 10-cm-diameter spherical volume, with a peak-to-peak variation of 3.2 ppm, which is better than the manufacturer's expected specification of 5 ppm. A water-filled sphere of 10 cm diameter gave a half-height linewidth of 0.14 ppm after a small amount of additional touch-up shimming. The field homogeneity as corrected is much improved over its original state, allowing the acquisition of improved spectra from samples of a size several centimeters in each linear dimension. Thus the field homogeneity is more useful for in vivo spectroscopy, the purpose for which the magnet was intended.