Effect of ultrasonic vacuum drying on the structural characteristics of whole-egg protein powder

This study investigated the effect of single- and dual-frequency ultrasonic vacuum drying on protein structure, endogenous fluorescence spectrum, surface hydrophobicity, sulfhydryl group content, emulsification, and emulsification stability of whole-egg powder. Experiments were carried out using the infrared spectroscopy, fluorescence spectroscopy, and ammonium salt of 8-phenylamino-1-naphthalene sulfonate (ANS) fluorescent probe methods. The ultrasonic treatment changed the secondary structure of proteins in whole-egg powder, increasing the content of α-helix, random curl, and β-rotation structures, and decreasing β-folding content. Ultrasonic treatment promoted the gradual transformation of the disulfide bond conformation of the sample from the twist-twist-twist conformation to the twist-twist-trans. Tyrosine and tryptophan residues in the samples were exposed, and the intensity ratio of the Fermi resonance spectra of tryptophan (I1363/I1338) in the single-frequency treatment, dual-frequency treatment, and the control group was significantly different (P < 0.05). The fluorescence intensity of the whole-egg powder samples treated with single and dual-frequency ultrasound was significantly reduced, and surface hydrophobicity and emulsification were significantly improved after ultrasonication, compared with that of the control group. However, the emulsification stability and sulfhydryl content were decreased. This research will be valuable to optimize whole-egg protein production and broaden its applications.