Insights into the Binding Mechanism of Polyphenols and Fish Myofibrillar Proteins Explored Using Multi-spectroscopic Methods

As the most abundant protein existing in fish, myofibrillar protein (MP) is likely to hydrolyze which affects the quality of fish during preservation. Polyphenols, which are some of the most popular antioxidants and antimicrobials, have been widely used in freshwater fish preservation and storage to prevent protein degradation. However, their binding behavior and mechanism is still unclear. In this study, the binding mechanisms of two types of polyphenols (chlorogenic acid (CGA); quercetin (QUE)) and MP extracted from grass carp were investigated through multi-spectroscopic methods. Different spectroscopic methods (fluorescence spectroscopy and synchronous fluorescence spectroscopy) were used to explore the interaction modes between polyphenols and fish-extracted MP. In addition, circular dichroism spectroscopy was used to detect microstructure changes of MP under different preservation approaches. Results showed that nanocomposites were generated when MP interacted with either CGA or QUE. The addition of CGA did not affect the α-helix content of MP, whereas QUE diffused the β-turns of myofibrillar proteins and promoted the formation of α-helices. At the same time, the fluorescence-quenching effect of CGA/QUE on MP was static quenching, and the binding constants, number of binding sites, and corresponding thermodynamic parameters of MP were calculated. It was concluded that the binding of CGA to MP depends on Van der Waals forces and hydrogen bonds, while QUE binds to MPs on the basis of electrostatic interactions. In addition, the fluorescence quenching of MPs with CGA is related to tryptophan and tyrosine residues, while the fluorescence-quenching effect of QUE on MPs is related only to tryptophan residues.