Combination of NMR and MRI Techniques for Non-invasive Assessment of Sea Cucumber ( Stichopus japonicas ) Tenderization During Low-Temperature Heating Process

The purpose of this study was to develop and test the combination of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) method to assess the proton changes of sea cucumber body wall during low-temperature heating process. NMR relaxometry and MRI measurements indicated a significant proton change in the internal structure for sea cucumber body wall when the heating temperature increased from 45 to 55 °C. Differential scanning calorimetry (DSC) analysis revealed that the denaturation temperature of sea cucumber body wall was in the range of 45–55 °C with an endothermic peak at 51 °C, which is in accordance with the result observed in NMR and MRI. Rheological study showed similar trend to the DSC thermogram. The band change in amide I region of Fourier transform infrared (FTIR) spectra indicated the decrease in α-helix content and possible formation of other secondary structures. Scanning electron microscopy (SEM) further confirmed that the low-temperature heating did induce microstructure changes. The analysis of the Ringerʼs soluble fraction (RSF), enzyme-labile fraction (ELF), and total unaltered fraction (TUF) for sea cucumber body wall during low-temperature heating provided more detailed information on the cause of structure change observed in NMR and MRI. The NMR parameters were highly correlated with the rheology storage modulus (G′), relative enzymatic assay parameters, RSF, ELF, and TUF. All these results demonstrated that it could be possible to use NMR and MRI to assess sea cucumber tenderization during low-temperature heating process.