Study On The Structure And Properties Of Egg White Picked With Mental Ions

Studies on physicochemical changes and the relevant mechanism of production of traditional foods is one of the most important scientific problems. Salt-curded eggs are one of the most famous traditional foods in China. The egg yolk and white have suffered a series of physicochemical changes during pickling. The changes and the mechanism of salt egg albumen are surprisingly less studied than egg yolk, most studies only observed an increase in salt and decrease in moisture and viscosity. In this experiment, the changes of thick white and thin white during salting as well as effect of metal ions on rheology and gelation properties of egg protein has been studied with fluorescence probe, circular dichroism and rheological analysis methods, to fill the theory gap and enrich the foundation of science of egg product. The major findings are as follows:The contents of metal ions increased with increasing salting time until the 20th day, while the contents of moisture decreased, and the pH egg white decreased from alkaline 9.5 to neutral. No difference was observed in the contents of metal ion, moisture contents and pH between thick white and thin white.The diffusion velocity were higher for univalent ions than divalent ions in the following order, Na+>K+>Mg2+>Ca2+>Zn2+. But the changes of moisture content were more noticeable for the divalent ions (Mg2+ and Ca2+) than with univalent ions, the moisture of samples dealed with zinc salts changed minimum. Divalent ions also have more significance on the effect of pH than univalent. The albumen index of most salted egg whites were decreased when salting time increased. For zinc salt samples the albumen index were first increased, and then reduced after the 5th day.The sorts and content of metal ions were important affecting factors for rheological properties of egg white. Both thick white and thin white were pseudo plastic fluids. During salting, no significant decrease in the apparent viscosity of thick white were found, while the thin white samples picked with Na+, K+, Mg2+ and Ca+ decreased gradually. For zinc salt, they made the apparent viscosity of thin white increased sharply at the beginning of pickling then decreased. The results of frequency dependence dynamic measurement suggest that thick white except zinc salt samples could be referred to physical gels, while thick white dealed with zinc salts became strong gels. The thin white without ions also belonged to physical gel system, and turn to entanglement network system after pickling.The effect of metal ion on gelation mainly includes postpone the speed of gelation and influence the process and properties of gel. The gelation time and temperature were raised with the increase in metal ion content. For Sodium, potassium, magnesium and calcium salts, the hardness, chewiness and gumminess of heat-induced thick white gelation were decreased significantly accompanied with salting continued, whereas the decrease in cohesiveness, springiness and resilience. The gel properties of thin white were higher than thick white, and the gel properties reduced less remarkable. For zinc salt, the sharpest decrease were noticeable in hardness, chewiness, gumminess of the samples, the cohesiveness and springiness also decreased markly, and the samples almost lost their resilience, and no significance gel transition were obtained during heating. The kind and content of cation were also the major factor affecting gel properties, and the order of cations effectiveness was in agreement with Hofmeister series of salts.The effect of mental ion on the gelation property and rheology were due to the changing of conformation and then altered the assembly of molecules. During pickling, the formation of (β-sheet structures were increased with salt 23 days picked, and the surface hydrophobicity decreased. The further increase inβ-sheet and a decrease in a-helix were found in heat-denatured egg protein, as well as accretion of surface hydrophobicity. The univalent ions and divalent ions can change the conformation of egg protein, and accelerate radom aggregation. These effects reduce cross-link of intermolecular, produce a coarse, open, uneven gel network, and decrease gel properties. Divalent ions also have more significance on the effect of conformation and microstructure of egg gel than univalent.