Spectroscopic imaging: Nuclear magnetic resonance and Raman spectrometry for the detection of collagen cross-linking from giant squid mantle, fin, and tentacle tissues

The application of proton nuclear magnetic resonance (¹H-NMR) imaging and Raman spectrometry is described for the detection and structural characterization of collagen cross-linking (pyridinoline) in soluble and insoluble collagen fractions obtained by cation-exchange separation of the mantle, fins, and tentacles of giant squid (Dosidicus gigas). The pyridinoline was detected using a fluorometric procedure only in the soluble collagen fractions. However, the pyridinoline was detected using high-performance liquid chromatography (HPLC) only in the insoluble collagen fraction from the tentacles. Meanwhile, in all samples, pyridinoline was detected by ¹H-NMR and Raman spectrometry. The higher peak intensities in both methods were observed in the insoluble collagen fraction from the tentacles. The muscles showed a lower decrease in shear force after 30 min of cooking. ¹H-NMR and Raman spectrometry provides an assay which is more sensitive than fluorescence and HPLC for pyridinoline detection in squid tissues, suggesting greater potential for the analysis of different types of tissue and collagen fractions.