Effects of power ultrasound on oxidation and structure of beef proteins during curing processing

• Ultrasound treatment (PUS) could increase lipid and protein oxidation significantly.
• Protein aggregation occurred according to SDS–PAGE analysis.
• Free sulfhydryl contents and protein surface hydrophobicity increased after PUS.
• FTIR showed the increases in β-sheets while decreases in α-helix structures after PUS.

The aim of this study was to evaluate the effects of power ultrasound intensity (PUS, 2.39, 6.23, 11.32 and 20.96 W cm−2) and treatment time (30, 60, 90 and 120 min) on the oxidation and structure of beef proteins during the brining procedure with 6% NaCl concentration. The investigation was conducted with an ultrasonic generator with the frequency of 20 kHz and fresh beef at 48 h after slaughter. Analysis of TBARS (Thiobarbituric acid reactive substances) contents showed that PUS treatment significantly increased the extent of lipid oxidation compared to static brining (P < 0.05). As indicators of protein oxidation, the carbonyl contents were significantly affected by PUS (P < 0.05). SDS–PAGE analysis showed that PUS treatment increased protein aggregation through disulfide cross-linking, indicated by the decreasing content of total sulfhydryl groups which would contribute to protein oxidation. In addition, changes in protein structure after PUS treatment are suggested by the increases in free sulfhydryl residues and protein surface hydrophobicity. Fourier transformed infrared spectroscopy (FTIR) provided further information about the changes in protein secondary structures with increases in β-sheet and decreases in α-helix contents after PUS processing. These results indicate that PUS leads to changes in structures and oxidation of beef proteins caused by mechanical effects of cavitation and the resultant generation of free radicals.