title: Combined high-field 13C CP MAS NMR and low-field NMR relaxation measurements on post mortem porcine muscles.
abstract: Changes in postmortem muscle characteristics are investigated in muscles from eight pigs exposed to different combinations of preslaughter stress (exercise on treadmill) and stunning method (CO(2) vs electrical stunning). Solid-state (13)C cross-polarization (CP) magic-angle spinning (MAS) NMR experiments are carried out on a total of 16 rapidly frozen M. longissimus muscle biopsies taken in vivo the day before slaughter and at 45 min postmortem. Simultaneously, low-field NMR T(2) relaxation time measurements are carried out on samples from M. longissimus. Glycogen and lactate are estimated from the (13)C CP MAS spectra, and correlations of r = 0.89 and r = 0.70, respectively, to subsequent biochemical determinations using partial least squares regression (PLSR) are established. Moreover, PLSR reveals that, besides the 72 ppm signal (carbons in glycogen), a signal around 38 ppm, which increases concomitantly with lactate, is also significantly correlated to changes in glycogen/lactate. With the assumption that the 38 ppm signal reflects CH(2) in phosphocreatine/creatine, altered mobility of creatine as a result of dephosphorylation is indicated. Finally, PLSR on the 45 min (13)C CP MAS spectra also reveals correlation (r = 0.54) to the slowest relaxing T(2) population (50 min postmortem), known to reflect extra-myofibrillar water. Subsequently, evaluation of the loading plot in the PLSR analysis reveals that the correlation exclusively is associated to the 52 ppm resonance intensity. With the assumption that this resonance reflects methyl groups in choline/phosphatidyl choline, the intensity changes in the 52 ppm resonance imply alterations in membrane properties. Accordingly, the data indicate a relationship between membrane properties and the amount of water being expelled from muscle cells postmortem, which supports the hypothesis that disruption of membranes is implicated in the postmortem mobilization of muscle water.
authors.affiliation: Department of Food Science, Danish Institute of Agricultural Sciences, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark. HanneC.Bertram@agrsci.dk
authors.forename: Hanne Christine
authors.initials: HC
authors.lastname: Bertram
authors.forename: Hans Jørgen
authors.initials: HJ
authors.lastname: Jakobsen
authors.forename: Henrik Jørgen
authors.initials: HJ
authors.lastname: Andersen
mesh_terms: D000818:Animals; D001834:Body Water; D002462:Cell Membrane; D006003:Glycogen / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000032:analysis; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D018482:Muscle, Skeletal / Q000737:chemistry*; D011180:Postmortem Changes; D013552:Swine
chemical_list: D019344:Lactic Acid; D006003:Glycogen