Abstract: In this paper Raman spectroscopy was used to study the changes of protein structure and amino acid residue microenvironment in grass carp surimi during frozen storage. Grass carp surimi was frozen at ?18 ℃ for 2 or 8 weeks and then scanned with a Raman spectrometer. The amide III region, C—C, S—S, and C—H stretching vibration bands were analyzed as well in the variation in I850/I830 intensity ratio, and the secondary structures of proteins in the amide I region were quantified. The results showed that the protein backbone conformation was transformed from an ordered to disordered state. The contents of α-helix and random coil structure in fresh surimi were 34.31% and 13.47%, respectively, which decreased to 15.33% and increased to 30.89% after 8 weeks of frozen storage, respectively. The I850/I830 intensity ratio was 1.81, 1.89 and 1.99 for fresh, two-week-frozen and eight-week-frozen surimi, respectively. Tyrosine residues were exposed to the surface of polypeptide chains during surimi processing and this phenomenon was more significant after frozen storage. The conformation of some disulfide bonds was transformed from trans-gauche-trans to gauche-gauche-trans within 2 weeks of frozen storage. The Raman peak of C—H stretching vibration near 2 900?cm-1 was weakened whereas the hydrophobic interaction of aromatic amino acid side chains was enhanced. The structure of surimi proteins became disorderly and scattered with micro-environmental changes of amino acid residues during frozen storage.

Key words: Raman spectroscopy, protein structure, frozen storage, grass carp surimi, amino acid residue