| Egg yolk is a natural ultra-stable emulsification system assembled from water,lipid and protein.Its stability is closely related to the specific assembly structure of protein and lipid in egg yolk.At present,the characteristic changes of egg yolks and their components during ultrasonic physical processing and their related mechanisms have not received attention.In this study,the high-intensity ultrasonic treatment(HIU)was used as the scene.Through the research on the structure and physical and chemical characteristics of egg yolk and its components under HIU treatment,the related mechanism of the changes in the functional properties of egg yolk during HIU treatment was initially explored.The main results are as follows.First,the effect of high-intensity ultrasonic treatment on egg yolk functional properties and component aggregation structure was studied.After HIU treatment,the emulsifying activity,emulsifying stability and foaming capacity of egg yolk solution were increased by 4.27-7.07%,5.40-31.87%,and 108.33-63.88%,and the thermal gel properties were also enhanced,but the foam stability decreased by 7.23-34.89%.SDSPAGE results showed that there was no significant change in the yolk protein bands,indicating that the yolk protein did not undergo covalent crosslinking or degradation.The HIU treatment increased the Zeta-potential of the egg yolk component in the aqueous solution(increased by 12.28-15.31%)and the content of free sulfhydryl groups(increased by 4.30-13.64%).In addition,the average particle size of the egg yolk component in the solution was significantly reduced,and the particle size distribution changed significantly.It is speculated that HIU treatment may cause the aggregation of egg yolk low-density lipoprotein and the partial dissociation of egg yolk granules.These results show that HIU treatment can affect the solution properties of egg yolk by changing the aggregation of egg yolk components,and ultimately lead to changes in the functional properties of egg yolk.On this basis,the mechanism of the effect of HIU treatment on the aggregation structure and functional properties of yolk granules was further studied.Based on the results of SEM,protein conformation and particle size analysis,it was confirmed that the HIU treatment induced partial dissociation of the yolk granules,causing a significant change in their aggregation state.After HIU treatment,the emulsifying activity(3.78-9.54%),Zeta-potential(6.24-97.09%)and surface hydrophobicity(2.92-10.52%)of the yolk granule were improved,and the free sulfhydryl groups content(3.41-9.38%)was decreased.SDS-PAGE results showed that ultrasound treatment did not cause cross-linking or degradation of protein molecular subunits in the yolk granules.In addition,after centrifugation of the yolk granule solution treated by ultrasound,the content of dry matter,soluble protein,calcium,and phosphorus in the supernatant increased,indicating that ultrasonic treatment can cause the dissolution of some substances in the yolk granules.These results indicate that HIU treatment can induce a certain degree of deagglomeration of the yolk granules,leading to changes in the surface properties of the yolk granules and dissolving some of the substances in the particles.These changes ultimately have an impact on the functional properties of the yolk particles.In addition,the effects of physical processing(HIU)and solvent treatment(ethanol treatment)on the molecular aggregation and properties of yolk LDL were compared.HIU treatment can improve the solubility and emulsion stability of LDL,and increase its Zeta-potential(119.56%)and surface hydrophobicity(10.81%).Based on particle size analysis and transmission electron microscopy analysis,LDL partially aggregated after HIU treatment,the average particle size increased by 15.69%,and the protein molecular interface became softer.After ethanol treatment,the solubility,emulsification activity and emulsion stability of LDL decreased by 74.75%,46.91% and 81.58%,respectively,and the average particle size of LDL increased by 13.3 times to 937.85 nm,indicating that ethanol treatment induced extensive aggregation of LDL.These results initially revealed the mechanism of the influence of physical processing(HIU)and solvent processing(ethanol)on the functional properties of egg yolk LDL. |
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