Raman spectroscopic study of structural changes in hake (Merluccius merluccius L.) muscle proteins during frozen storage

This paper examines changes in the structure and functionality of fish muscle proteins at frozen storage temperatures known to render very different practical storage lives (-10 and -30 degreesC). Apparent viscosity and dimethylamine (DMA) content showed drastic temperature-related differences during storage. Raman spectroscopy revealed the occurrence of some structural changes involving secondary and tertiary protein structures. The changes in secondary structure were quantified, showing an increase of beta-sheet at the expense of alpha-helix structure. The vC-H stretching band near 2935 cm(-1) increased in intensity, indicating denaturation of the muscle proteins through the exposure of aliphatic hydrophobic groups to the solvent. These structural changes were more pronounced at -10 degreesC but occurred at both storage temperatures, whereas changes in apparent viscosity and DMA only occurred in storage at -10 degreesC. The possible utility of these structural changes for quality assessment is discussed.