Elucidation of the effect of formaldehyde and lipids on frozen stored cod collagen by FT-Raman spectroscopy and differential scanning calorimetry

The effect of frozen storage (-10 and -30 degreesC), formaldehyde, and fish oil on collagen, isolated from cod muscle, was investigated. Salt- and acid-soluble collagen fractions as well as insoluble collagen indicated changes in solubility on frozen storage. Differential scanning calorimetry (DSC) showed a highly cooperative transition at 28.2 degreesC for isolated collagen. Changes in the thermodynamic properties of collagen were observed on frozen storage at -10 degreesC compared with the control at -30 degreesC because of changes in structure. In the presence of formaldehyde, there were no changes in the DSC collagen transition; however, in the presence of fish oil there was an increase in enthalpy and an extra peak was observed at 44.6 degreesC, indicating collagen-fish oil interaction. Structural changes resulted in a decrease in the solubility of collagen in salt and acid solution. FT-Raman spectra obtained for collagen at -10 degreesC and -30 degreesC confirmed the alteration of the conformation of coliagen not only at -10 degreesC but also in the presence of formaldehyde and fish oil.