Analysis of "soft flesh"-affected Atlantic mackerel based on a systematic study of histology and protein structure

This study focused on the "soft flesh"-affected Atlantic mackerel caused by Kudoa under different degradation levels and investigated the changes of tissue morphology, protein structural characteristics, and protein molecular weight. Results showed that the protease activity of cathepsin L in "soft flesh"-affected Atlantic mackerel was positively correlated with the degree of myoliquefaction. With the onset of myoliquefaction, a fragmentation of muscle fibers was observed, accompanied by a concurrent increase and subsequent decrease in free sulfhydryl groups and surface hydrophobicity. The results of gel electrophoresis confirmed that myoliquefaction were primarily associated with the degradation of myosin heavy chains. Additionally, the degraded protein had a molecular weight of approximately 150 kDa and was primarily composed of myosin rod. Fourier transform infrared spectroscopy revealed that the relative content of α-helix structure rose while that of β-sheet structure decreased as myoliquefaction occurred. Collectively, these findings suggested that the alterations in protein structure within "soft flesh"-affected Atlantic mackerel, particularly in secondary structure, could serve as effective tools to distinguish myoliquefied meat.