Effect of Ultrasonic Treatment on Protein Structure and Physicochemical and Foaming Properties of Liquid Egg White

The effect of pulsed ultrasonic treatment on the foaming properties, Raman spectroscopy, endogenous fluorescence spectroscopy, static rheological properties, particle size, physicochemical properties and structural characteristics of liquid egg white (LEW) was investigated. Correlation analysis was also conducted. The results showed that the disulfide bond conformation of egg white protein (EWP) was changed by ultrasonic treatment, and the viscosity and total sulfhydryl group content of LEW were decreased accordingly. LEW was still a pseudoplastic fluid after ultrasonic treatment. The particle size, surface sulfhydryl content, thermal denaturation enthalpy (ΔH) and α-helix and β-sheet contents of EWP gradually decreased with increasing ultrasonic treatment time up to 15 min, whereas the endogenous fluorescence intensity and surface hydrophobicity increased. The tryptophan residues tended to be exposed on the protein surface. Meanwhile, the foaming capacity was gradually improved, and the foam stability was reduced marginally. The micromorphology of the foam was smaller and more evenly and closely arranged after ultrasonic treatment. The content of β-sheet continued to decrease with increasing ultrasonic time, whereas the opposite was observed for particle size, surface sulfhydryl content, ΔH, α-helix content, intensity ratio of tryptophan residues (I1 363/I1 338) ratio, endogenous fluorescence intensity and surface hydrophobicity. Meanwhile, foaming capacity gradually decreased, while foam stability increased. The correlation analysis showed that foam capacity was positively correlated with I1 363/I1 338 ratio and surface hydrophobicity, and negatively correlated with surface sulfhydryl content, ΔH, average particle size, and α-helix content. In addition, foam stability was negatively correlated with surface hydrophobicity. © 2019, China Food Publishing Company. All right reserved.