Effects of Different Drying Methods on Physicochemical and Functional Properties of Egg White Protein

In order to explore the effects of different drying methods on the functional characteristics and the internal mechanism of egg white protein (EWP), egg white protein powder was prepared by spray drying or vacuum freeze drying, respectively. The protein structure, physicochemical properties and functional properties of spray dried egg white powder (EWP-P) and freeze dried egg white powder (EWP-D) were studied. The results showed that compared with the liquid egg white (EWP-C), spray drying could greatly decrease the endogenous fluorescence intensity of EWP, while improve the surface hydrophobicity and free sulfhydryl group content. Fourier transform infrared spectroscopy showed that the α-helix, β-fold and β-turn of EWP-P were 16.30%, 25.72% and 40.23%, respectively, and EWP-D were 20.43%, 24.32% and 35.69%, respectively. Under different pH, the solubility of EWP-D was higher than EWP-P, and the surface tension was lower than EWP-P. In addition, the contact angle of EWP-P was 99.62°, which was higher than EWP-D (65.97°), indicating that spray drying could significantly improve the hydrophobicity of EWP. The emulsifying ability index, emulsifying stability index and foaming characteristic of EWP-D were higher than EWP-P at different pH values, but the foaming stability of EWP-D was lower. The results of fluorescence inverted microscope and confocal laser scanning microscope showed that the liquid droplets of EWP-D emulsion were smaller and more uniform, and the emulsion stability was higher than EWP-P. In conclusion, EWP-P had higher contents of β-fold structures and free sulfhydryl groups on the surface, and higher surface hydrophobicity, which resulted in the better gel properties. EWP-D had lower surface hydrophobicity, smaller surface tension and greater solubility, thus possessed the better emulsifying capacity and foaming characteristic.