Influence of repeated freeze–thaw treatments on the functional and structural properties of myofibrillar protein from mirror carp (Cyprinus carpio L.)

The influence of repeated freeze–thaw (F-T) treatments (0, 1, 3 and 5) on the functional and structural properties of myofibrillar protein (MP) from mirror carp (Cyprinus carpio L.) was investigated according to the changes in rheological properties, particle distribution, Zeta (ζ)-potential, molecular force, Fourier transform infrared (FTIR) spectra and sulfhydryl content. After F-T treatment with five cycles, a significant decrease in the storage modulus values (G'), loss modulus values (G), ζ- potential, total sulfhydryl content and reactive sulfhydryl content of MP was observed (P < 0.05). The particle size increased within the third F-T cycles, but it decreased in the fifth F-T treatments (P < 0.05). The hydrogen bonds, hydrophobic interactions and disulfide bonds of protein were broken during multiple F-T treatments. In addition, as the F-T cycles increased, the α-helix and β-turn contents decreased (P < 0.05), and the β-sheet and random coil content increased (P < 0.05). Therefore, repeated F-T treatments damaged the structure of MP and reduced the functional properties of MP from mirror carp.