Interaction Mechanism of Moderately Oxidized Myofibrillar Proteins with Selected Aldehyde Compounds

A hydroxyl radical generating system consisting of 0.1 mmol/L FeCl₃, 0.1 mmol/L ascorbic acid, and various H₂O₂ concentrations (0, 0.25, 0.5, 1.0, 2.5, 5, 10 and 25 mmol/L) was established and used to investigate the interaction mechanism of differently oxidized myofibrillar proteins (MPs) with 3-methyl butanal, pentanal, hexanal and heptanal. First, the binding capacity of oxidized MPs to the four aldehydes were determined by gas chromatography-mass spectrometry (GC-MS). Then, ultraviolet (UV) absorption spectroscopy, fluorescence spectroscopy (quenching mechanism and thermodynamic analysis) and circular dichroism (CD) spectroscopy were used to reveal the interaction mechanism between oxidized MPs and aldehydes. The results showed that heptanal had the strongest binding capacity with MPs, and the binding capacity of oxidized MPs with a H₂O₂ concentration of 1.0 mmol/L to all four aldehydes was the highest (P < 0.05). UV absorption spectra and fluorescence spectra demonstrated that oxidized MPs interacted with the four aldehydes via static and dynamic quenching. The maximum absorption peaks of both tyrosine and tryptophan residues were red-shifted with an increase in heptanal concentration, indicating that the tyrosine and tryptophan residues of MPs were exposed to a more hydrophilic environment. Thermodynamic analysis showed that the interaction between MPs and heptanal was mainly driven by hydrophobic interaction. The CD spectra showed that the α-helix content decreased from 19.24% to 16.88% (P < 0.05) and the β-sheet content increased from 24.59% to 26.47% (P < 0.05) with increasing heptanal concentration, and the structure of MPs changed from the ordered to the disordered state. This study provides a theoretical basis for flavor regulation of meat products.