Research On High Pressure And Heat Treatment On The Protein Of Egg Yolk

Hen's egg yolk (EY) is a key ingredient in many food products. Egg proteins add a high nutritional value to egg containing foods and they are also associated with several functional properties for industrial applications. These include gel formation, foaming capacity and emulsifying ability among others. To ensure that egg products are free from pathogenic bacteria and particularly Salmonella, egg yolk need to be pasteurized under certain conditions. Egg processors are concerned about these time-temperature treatments because the products should not only be microbiologically safe but should also perform satisfactorily.Egg yolk was fractionated by a low speed centrifugation into granules and plasma. The composition, solubility and emulsifying properties of granules and plasma were investigated. SDS-PAGE indicated that plasma contained mainly low-density lipoproteins (LDL) and livetin, high-density lipoprotein (HDL) and phosvitin in granules. The solubility was different at different salt concentrations. At iron strength 0.5M sodium chloride, the protein solubilities were above 90%. And at this solubility we found plasma had the best emulsifying activity and granules the best emulsion stability.The effects of high pressure (HP) treatment on some physicochemical and functional properties of egg yolk were investigated. The viscosity, protein solubility, emulsifying activities, emulsion stability, differential scanning calorimetric characteristics, surface hydrophobicity (H0), free sulfhydryl (SH) content were evaluated. HP treatment at 100-500MPa resulted in a decline in solubility, and a slight decline in H0. Free SH content of EY was significantly decline after HP treatment at 300MPa. HP treatment at 100MPa slightly decreased emulsifying activities, but increased emulsion stability.Then we investigated heat treatment on the properties of EY. The emulsifying properties, extent of protein denaturation, free sulfhydryl content and rheology properties were investigated in various thermal conditions. Most of the yolk were turned into gel after 3.5min at 68℃. Other properties were the same at 62℃and 65℃. Native-PAGE indicated theγ-vitelline denaturated after 2.5min at 62℃. We also studied other properties of yolk protein at 65℃from different times including viscosity, surface hydrophobicity and protein solubility. We found the hydrophobic groups revealed after 3.5min at 65℃. They might collect again if prolonged the time. The protein denaturation told us it was a reversible process.FTIR indicated the second structure of yolk protein:β-replicate32.6%,β112.83%,α-helix15.85%,T-corner18.58%,γ20.15%。...