Research On The Emulsifying Property Of Phosvitin From Hen Egg Yolk

Deep processing of functional active ingredients was an effective way toimprove the value-added and expand the industrial application of egg products. Pv,from hen egg yolk, was a protein with high content of phosphours. The core in theform of an elongated chain contained negatively charged phosphatidylserine. Phosvtinacted as a bipolar molecule with the hydrophic amino acid in the C-terminal. Itshowed an application potential as the natural biosurfactant in food, medical, andcosmetic industry. Generally, the components in food system would have an interationwith Pv and then influenceits emulsifying behavior, and there was barely literature onthis subjuct. At the same time, the little hydrophobic terminal in Pv would limit itsabsorption behavior in the interfacial layer of oil-in-water. The lack of branchedstructure in Pv would aslo limit the forming of an effective steric-hinerance instabilizing the oil-in-water emulsion. In our research, the improvement technologyfrom both the external and internal points of view was tried to enhance theemulsifying property of Pv. The physicochemical properties were also characterizedto better understand the mechanism of emulsifying actions.Two Pv-isolated technology, salty and PEG, were applicated to extract Pv fromhen egg yolk with no organic solvent used. The yield and N/P ratio of Pv by saltymethod were91.05%and3.45respectively. The proportions of polar and hydrophobicAA residues were70.7%and19%respectively. At the same time, the secondarystructure of Pv was loose and the unfolding structure accounded for91%. Theemulsifying activity index (EAI) and emulsion stability index (ESI) of Pv were19.80and67.60resepctively, higher than that of sodium caseinate (Sc). However, thefoaming capacity (FC) was12.42%, lower than that of soybean protein isolated (SPI).The yield and N/P ratio of Pv by PEG method was49.28%and2.89respectively. Theproportions of polar and hydrophobic AA residues were80.2%and13.5%respectively. Part of hydrophic properties of Pv were screened and the secondarystructure was changed by PEG6000. The proportion of α–helix and β–structure(including β–folding and β–turn) were17%and26%respectively, and the unfoldingforms occupied of35.8%. The EAI and ESI of Pv isolated by PEG method were11.37and49.89respectively, lower than that by salty method. The FC was only8.33, alsolower than that of SPI.The normal food additives, such as glycerol, pectin and trehalose showed asynergistic interaction with Pv on the emulsifying behavior. The presence of0.5% glycerol significantly increased EAI of Pv from19.8to20.9and ESI from67.6to75.1. The addition of0.1%pectin and0.5%trehalose also resulted in a betteremulsion stability of Pv. The pattern of CD spectra indicated a typical unfoldingsecondary structure, and all the tested additives displayed slight effect on theunfolding structure of Pv. Furthermore, fuorescence spectra pattern demonstrated thatglycerol and trehalose increased the hydrophobicity of Pv, while pectin showed anopposite effect. All emulsions exhibited a shear-thinning behavior and the fowbehavior was ftted to the power law model. Frequency sweeps of all tested emulsionsillustrated that they behaved like a viscous liquid.To enhance the steric hindrance effect of Pv and in turn improve the emulsionstability, the Pv-Dex conjugates were prepared in an aqueous solution at the initialstage of Maillard reaction. The optimum conjugation condition chosen was per Pvglycosylated with4-fold dextran (Mw40kDa) at100℃for6h. The content of freeamino groups in the glycosylated Pv decreased to77.4%. The new bandII inSDS-PAGE gel and the shift of main peak in SE-HPLC from9.16min to8.87minand the minor peak from6.56min to6.13min both confirmed the formation ofcovalent conjugates. CD spectra demonstrated that the unfolding structure decreasedto72.1%, and α–helix increased to20.8%after glycosylation reaction. No significantdifference occurred to the solubility of Pv after conjugation with Dex when pH rangedfrom5.0to8.0, but a remarkable increase from53.0%to79.3%appeared at pH4.0.The hydrophobicity was decreased and the surface charges were slightly screenedafterDex attaching to Pv, while the interfacial thickness of Pv was prominentlyincreasedat the acidic condition. The emulsifying properties characterized byturbidimetric method, droplet-size distributions and confocal laser scanningmicroscopy illustrated that glycosylation of Pv would be an effective method toimprove the emulsion stability against unfavorable pH environment.To link a hydrophobic tail to Pv and then improve the emulsifying property andfoaming property, FA was activated through esterification and then attached to Pvthrough acylation. The slight higher andwider bands in SDS-PAGE gel indicated thatdifferent carbon chain length of FA had been convalent binded to Pv. Differentdegrees of shift of maximum UV absorbance wavelength were caused by lauric acid(C12), myristic acid (C14), palmitic acid (C16) grafting with Pv, and the absorbanceswere in the following order: Pv-C14＞Pv-C16＞Pv-C12. The reaction extent of C12,C14and C16with Pv were16.45%，30.56%，27.02%respectively and the solubilityof relevant products decreased to51.00%56.77%22.14%respectively. The unfolding structure was also increased from35.8%to38.3%69.3%45.6%respectively. Pv-C14displayed the highest EAI of16.26, ESI of74.41, and FC of33.33%in the neutral condition, and showed the strongest resistance to theunfavorable pH environment. Pv-C12also increased the EAI to14.54, ESI to62.23,and FC to20.83%, and resulted in a certain resistance to acidic conditions. Pv-C16enhanced FC to28.57%. All the resultes demonstrated that the covalent binding of FAto Pv was an effective way to improve the processing properties of Pv.