The present paper investigated gel properties and secondary structures of egg white-bovine gelatin composite hydrogels with different mass ratios upon ultrasound and transglutaminase pretreatment. The free sulfhydryl content increased with increasing gelatin in proteins mass ratio; however, longer probe sonication had an opposite effect on free sulfhydryl content and hydrogel solubility. The hydrogel solubility data revealed that proteins ratio and the pretreatment conditions (ultrasound duration and transglutaminase concentration) determined the contribution of non-covalent bonds (including electrostatic bonds, hydrogen bonds, and hydrophobic interactions) and covalent bonds (i.e., Ssingle bondS bridges) in the formation of composite hydrogels. Moreover, the hardness and storage modulus of hydrogels were improved with increasing gelatin in proteins mass ratio and ultrasound duration. Based on Fourier transform infrared spectroscopy and rheological data, helical structures had a great portion in composite hydrogels. Finally, the microstructure investigations showed that hydrogels formed the most porous structures at 50E:50G and 40E:60G (E: egg, G: gelatin) mass ratios.

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