于拉曼光谱解析冻藏过程中鱼糜蛋白的结构变化

采用拉曼光谱技术研究冻藏过程中草鱼鱼糜蛋白结构和氨基酸残基微环境的变化。草鱼鱼糜经－18?℃冻藏处理2?周和8?周后进行拉曼光谱扫描，得到光谱数据；对酰胺III区及C—C、S—S、C—H伸缩振动谱带进行解析，对比I850/I830强度变化，同时对酰胺I区蛋白质二级结构进行定量分析。结果表明：冻藏过程中草鱼鱼糜蛋白质主链构象由有序向无序发展，α-螺旋结构从新鲜状态的34.31%下降到冻藏8?周后的15.33%，无规卷曲相对含量从13.47%上升到30.89%；新鲜、冻藏2?周和冻藏8?周的鱼糜蛋白I850/I830分别为1.81、1.89和1.99，鱼糜加工过程使酪氨酸残基暴露在多肽链表面，冻藏引起暴露更加彻底；部分二硫键构象在冻藏初期（2?周内）基本完成由反式-扭式-反式向扭式-扭式-反式转变；2?900?cm－1附近C—H伸缩振动的拉曼峰减弱，芳香族氨基酸侧链疏水作用力增强。冻藏过程中鱼糜蛋白的结构逐渐疏散无序，氨基酸残基微环境发生改变。

Analysis of Structural Changes of Surimi Proteins during Frozen Storage by Raman Spectroscopy

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.