Chemical interactions involved in microwave heat-induced surimi gel fortified with fish oil and its formation mechanism

The present study was conducted to elucidate the gelation mechanism of surimi protein-fish oil composite gels heated by microwave. Changes in chemical interactions, secondary structures, protein profiles and microwave-absorbing ability were investigated. The results clearly indicated that microwave heating could markedly (P < 0.05) intensify non-covalent bonds (ionic bonds, hydrogen bonds, and hydrophobic interactions) formation. The significant (P < 0.05) decrease of sulfhydryl groups was consistent with remarkable (P < 0.05) increase of disulfide bonds, suggesting that microwave heating also promoted the covalent bonds crosslinking. Moreover, the appearance of polymerized protein band of SDS-PAGE indicated that mild oxidation induced by microwave heating is also a potential pathway for gel properties enhancement. Raman spectral analysis demonstrated that the a-helix content decreased to 45.55%, while the beta-sheet content increased to 26.85%, compared to the traditional heating. The results of microwave-absorbing ability analysis indicated that the reflection loss was decreased from -4.47 dB to -3.02 dB at 2450 MHz as the FO concentration up from 9% to 12%, indicating the decline 14.16% of microwave absorptivity. Similarly, the microstructure of gel heat-induced by microwave was more compact, thus resulting in a greater stabilization of liquid phase with avoidance of oil coalescence and water migration throughout the gel network. These results provide an understanding of gelation mechanisms of composite gels and electromagnetic interaction under microwave field, which could be meaningful for the functional surimi products fabrication.