Effect of ultrasound pretreatment with mono-frequency and simultaneous dual frequency on the mechanical properties and microstructure of whey protein emulsion gels

Abstract The effect of ultrasound pretreatment with mono-frequency ultrasound (MFU) and simultaneous dual frequency (SDFU) on rheology, texture, water holding capacity (WHC) and microstructure of whey protein emulsion gels was investigated. Also, the protein structure was displayed using circular dichroism and fluorescence spectrum. The Results showed that ultrasound could improve mechanical properties and change the microstructure of whey protein emulsion gel compared with the control. It was also found that, ultrasound could lead to decreasing in α-helix and increasing in random coil thereby exposing more tryptophan residues. As storage modulus (G'), texture hardness and WHC were negatively correlated with α-helix content, however, they had positive correlation with random coil content. Simultaneous dual frequency ultrasound exhibited the highest effect among the ultrasound pretreatments. It was indicated that the composite of oil droplet particulate aggregate network and protein aggregate network in the microstructure of emulsion gel might have resulted from enhanced molecular interactions of protein by ultrasound pretreatment. In conclusion, the dual frequency ultrasound was effective in improving the mechanical properties of whey emulsion gel when compared with the mono-frequency ultrasound.