Characterization of enzymatically modified liquid egg yolk: Structural, interfacial and emulsifying properties

Abstract

There is considerable interest in using enzymatic hydrolysis to control the rate and extent of egg yolk so as to develop the better-quality emulsions in food industry. The purpose of this study is to evaluate the effect of dual enzymatic hydrolysis of neutrase and trypsin on structural and emulsifying properties of liquid egg yolk (LEY) at varying hydrolysis times (0.5, 1.5, 2.5, 3.5 and 4.5 h). The results showed that the emulsifying activity, emulsification capacity and stability of emulsion of LEY could be enhanced after the enzymatic hydrolysis. The solubility of yolk proteins was increased from 24.2% to 58.0% over 1.5 h, with a degree of hydrolysis (DH) of 2.2%. The residual protein concentration at the continuous phase of emulsion was analyzed by SDS-PAGE. We also found hydrolysis could significantly increase the surface hydrophobicity. In addition, CD spectra was carried out to determine the secondary structures before and after the heat treatment. We have found that, not only the protein flexibility, but also the emulsion thermostability was improved after enzymatic hydrolysis. At last, the hydrolyzed LEY showed the superior emulsifying activity and capacity, while the emulsion prepared by it has excellent stability. This is consistent with the observation from ζ-potential and droplet size distribution. It was proved that, with the increase in solubility, surface hydrophobicity and molecular flexibility of the hydrolyzed proteins, emulsifying properties were improved.