Identification of the early postmortem metabolic state of porcine M. semimembranosus using Raman spectroscopy

The metabolic conditions in the early postmortem muscle determine meat quality. Raman spectroscopy is shown to follow the early postmortem metabolism (0.5–10 h) of porcine M. semimembranosus (N = 10). To this end the Raman spectra, pH and lactate kinetics were measured in the laboratory. Raman difference spectra were utilized to identify the spectral changes and to assign them to metabolic and structural alterations in the pre-rigor (50–120 min) and rigor (2–8.5 h) phases. In the Raman spectra, the decreasing pH was indicated by three signals assigned to phosphorylated metabolites and inorganic phosphate. Furthermore, the degradation of glycogen to lactate and a reduction of signal intensity of α-helical proteins were revealed. In the pre-rigor phase, degradation of phosphocreatine to creatine and reduction of oxy- to deoxymyoglobin was found. In the rigor phase, additionally, degradation of ATP to inosine monophosphate (IMP) was observed. Good agreement was achieved between measured and simulated Raman difference spectra. In the pre-rigor and rigor time frame, normal and deviating meat quality could be distinguished based on signals of phosphocreatine, ATP, IMP and α-helical proteins. This work provides a deeper understanding and the first semi-quantitative description of the early postmortem Raman spectra of meat which show potential for the non-invasive and early detection of the metabolic state of meat, and hence for the identification of deviating meat qualities.