Influence of ultrasound probe treatment time and protease type on functional and physicochemical characteristics of egg white protein hydrolysates

The objective of this study was to discover the relationship between the ultrasound probe treatment (UPT) on egg white proteins (EWPs) before EWPs hydrolysis by different proteases, and the functional properties of the obtained hydrolysates. To fulfill this goal, the protein solubility, foaming, and emulsifying properties were studied as a function of the UPT time and then related to the surface characteristics and structural properties. The changes in the hydrolysates microstructures and macromolecular conformation, induced by the UPT, were followed using scanning electron microscope analyzis (SEM) and Fourier transforms infrared spectroscopy (FTIR). The results showed that UPT influenced (P < 0.05) the proteolysis of egg white proteins for all examined treatment times. Alcalase hydrolysates (AHs) and papain hydrolysates (PHs) were found to have a higher solubility, as a consequence of their relatively higher foaming, and emulsifying properties compared to the untreated hydrolysates. The changes in surface hydrophobicity, sulfhydryl content and surface charge of AHs and PHs indicated unfolding of EWPs affected by ultrasound. SEM analyzis showed that UPT destroyed the microstructures of AHs and PHs, while FTIR spectra indicated remarkable changes in the macromolecular conformation of AHs and PHs after UPT. This study revealed that by combining ultrasound pre-hydrolysis treatment under controlled conditions with thoughtful proteases selection, hydrolysates with improved functional properties could be produced, enhancing utilization of EWPs in food products.