Effects of different ionic strengths on the physicochemical properties of plant and animal proteins-stabilized emulsions fabricated using ultrasound emulsification

In this study, high intensity ultrasound (HIU) was used to produce food protein stabilized emulsions under different ionic strengths (0, 25, 50, 100, 200 and 300 mM NaCl). Five plant and animal food proteins, whey protein isolate (WPI), soy protein isolate (SPI), bovine gelatin, peanut protein isolate (PPI) and corn zein were selected as protein emulsifiers. PPI and zein could not form emulsions using ultrasound emulsification at all ionic strengths (from 0 to 300 mM NaCl). However, ultrasound could induce stable emulsions using SPI, WPI and gelatin as emulsifiers. Moreover, different ionic strengths and protein types influenced the physicochemical properties of HIU induced emulsions obviously. It was found that the droplet sizes of gelatin emulsions were lower than those of SPI and WPI emulsions at salt concentrations of 300 mM NaCl. Furthermore, gelatin emulsions had better stability against environmental stresses (salt and temperature) than that of SPI and WPI emulsions. Moreover, the adsorbed protein (%) at the oil/water interface of SPI emulsions was higher than those of WPI and gelatin emulsions. However, the adsorbed protein amount of all proteins stabilized emulsions increased significantly after salt addition. The absolute 1-potential values decreased with the increase of salt concentrations. The microrheology results indicated that the SPI emulsions formed a gel-like structure at high salt concentrations (> 50 mM NaCl) as SPI emulsions exhibited higher elasticity than WPI and gelatin emulsions. In conclusion, the ultrasound as a green emulsification technique could be used to fabricate emulsions stabilized by plant and animal proteins.