Characterization of liquid egg yolks hydrolyzed by phospholipase: Structure, thermal stability and emulsification properties

Abstract

This study aims to clarify the difference between phospholipase A1 (PLA1) and phospholipase A2 (PLA2) in terms of hydrolyzing egg yolk (EY). The results indicated that the disintegration of the lipoprotein micelle structure after phospholipase hydrolysis induced an enhanced solubility of proteins. The solubility after PLA1 and PLA2 treatment (91.36 %/83.49 %) was significantly higher than that of the untreated egg yolk (27.89 %). Simultaneously, the disintegration of the lipoprotein micelle structure induced structural unfolding of proteins with hydrophobic chains buried inside the spatial structure, while charged amino acids and hydrophilic chains exposed on the surface. This structural deformation contributed to the increased thermal stability of EY, thereby increasing intermolecular electrostatic repulsion. In comparison, PLA1 hydrolyzed EY showed relatively better thermal stability than PLA2, due to the lower surface hydrophobicity. However, PLA2 hydrolyzed EY (up to 225 mL) had greatly higher emulsifying capacity than PLA1 (up to 159 mL), due to the better stability and emulsifying ability of the generated 1-lyso-phospholipase. Furthermore, we discovered that proteins and phospholipids jointly functioned at the interface to influence the particle size and stability of emulsions. Specifically, the emulsifying activity of phospholipids may play a more decisive role in determining the particle size, while the interfacial adsorption of proteins or protein particles may be more crucial in ensuring the stability of the emulsions. These findings had significant implications for the application and advancement of phospholipase-catalyzed egg yolk hydrolysis, providing practical guidance for the production of EY with high thermal stability or emulsifying capacity.

Keywords: Egg yolk; Emulsifying ability; Enzymatically hydrolyzed lecithin; Heat stability.