Mechanism of the Discontinuous Structure in Heat-Induced Natural Egg Yolk Mediated by Accumulation of Yolk Sphere Microgels: Morphology, 4D-DIA Proteomics, and Physicochemical Properties

The heat-induced natural egg yolk is a discontinuous object formed by the accumulation of yolk spheres. However, the reason why yolk spheres form individual microgels rather than continuous gels has not been elucidated. This study investigated the different gelation behaviors in the yolk sphere exterior (EYSE) and the yolk sphere interior (EYSI) by using 4D-DIA proteomics, electron microscopy, and multispectral techniques. Results demonstrated that vitellogenin-1, -2, and -3 (EYSI/EYSE fold change: 3.36, 3.53, and 2.42, respectively) were key proteins corresponding to continuous gel structure formation of EYSI. However, the high levels of apolipoprotein A-I (FC: 0.18) and heat shock protein found in EYSE with a special hydrophobic domain for lipid binding impeded the continuous gel formation. Thus, the EYSE formed some small-volume aggregates without continuous gel, which separated individually the microgel of yolk spheres. This study will provide theoretical guidance for the quality regulation of egg yolk products.