Study On Gel Formation Mechanism Of Preserved Egg White Gel Induced By Strong Alkali

Preserved egg is our traditional egg product,however,the researches related to the processing mechanisms on preserved egg are lacking,particularly those involving alkali-induced gel formation of egg white(EW)has not yet been elucidated.In this paper,the influence of preserved egg white(PEW)gel formation by strong alkali was emphasized.Changes in gel texture properties and microstructure were examined by means of low-field magnetic resonance(LF-NMR),rheometer,texture analyzer,and environmental scanning electron microscope(ESEM).The interaction forces between protein molecules was investigated by chemical method.Protein components involved in gelation were also examined using polyacrylamide gel electrophoresis(SDS-PAGE).Outside the egg shell,moreover,a model of EW gel induced by strong alkali was established,investigating the changes in gel properties in order to simulate the process of gel formation of PEW.Using Fourier transform infrared spectroscopy(FTIR),fluorescence and UV spectra examined the molecular structure information of ovalbumin during gel-formed in order to elucidate the molecular mechanism.It was aimed to elucidate the alkali-induced EW protein gel formation mechanism from the perspective of structure and function.This will be help for the rich in food protein gel system and the guidance in preserved egg processing in theoretical.The main contents and results are as follows:First of all,PEW gel characteristics during process were examined by LF-NMR and ESEM.The results showed that one part of moisture of inner egg migrated to the outside and other was fixed by gel formation because of the strong alkaline solution dynamic penetration.The microstructure presented a three-dimensional loose network structure which were the fibrous and sheet-like with regular distribution of the mesh.This was considered to be a polymer gel.With pickled time prolonged,PEW gel presented more better microstructure.The results of changes in the interaction forces showed that PEW gel was mainly supported by the ionic bonds and disulfide bond,both about 40%each,followed by hydrophobic forces,accounting for about 20%of the maximum.Ionic bonds gradually decreased,disulfide bond and hydrophobic interactions gradually increased with time extended.Self-assembly with formed a fibrous gel structure was related to the ionic bonds.Intermolecular disulfide cross-linking was derived from the oxidation reaction of thiol groups and exchange reaction between thiol groups and inner molecular disulfide bonds.SDS-PAGE showed that EW protein was degradation and formed polymer aggregates via ionic bonds,disulfide bonds and hydrophobic interactions.Ovalbumin as a main component played an important role in aggregating.Secondly,a model based on strong alkali-induced EW gel formation was established,highlighting the leading role of the strong alkali.The results showed that,outside the shell,the formed gel was weak with transparent or translucent.It would be liquefy by strong alkali treatment extended.Textural properties of TPA mode confirmed that the gel hardness and elasticity undergone dynamic changes,hardness decreased after a increase at first,elasticity decreased with time.ESEM images showed the same gel microstructure type as PEW gel basically,however,it became loose gradually in network structure and the mesh extended and fusion each other with treatment prolonged.The worse microstructure,the worse textural characteristics.Changes in the intermolecular forces showed that the gel was supported by a large number of ionic bonds,and low proportion disulfide bonds and hydrophobic interaction,almost no hydrogen bonds.More than 60%were ionic bonds,disulfide bond was less than 40%.With the time prolonged,ionic bonds gradually increased but decreased proportion of disulfide bond.The more disulfide bond,the higher the hardness.Intermolecular disulfide bonds will also be given by the thiol oxidation and disulfide bond exchange reaction of thiol group.SDS-PAGE showed that the proportion of EW proteins were degraded due to the strong alkali.Ovalbumin was involved in ionic bonds and disulfide cross-linked to form high molecular weight aggregates.Finally,ovalbumin was induced to form a gel by strong alkali,using the same system in the previous chapters examined its gelling properties and interaction forces.And using spectroscopy method including Fourier transform infrared spectroscopy(FTIR),fluorescence spectroscopy and UV spectra examined its molecular structure information influenced by alkali.The results showed that the formation of ovalbumin gel was consistent with the type of polymer gel.ESEM were also consistent with EW gel.Intermolecular forces were composed of a large number of ionic bonds(about 85%)and a small amount of the disulfide bond(about 5%).SDS-PAGE presented ovalbumin aggregates through ionic bonds and disulfide.ANS fluorescence showed that,under highly alkaline environment,ovalbumin molecules denatured rapidly and exposed their hydrophobic core,resulting the surface hydrophobicity increased rapidly.But surface hydrophobic decreased slowly in the gel state phase.FTIR spectra showed ovalbumin molecular structure changed,in which secondary structure were change into each other,resulting more β-sheet structure under alkali treatment and which related to the formation of aggregates.Intrinsic fluorescence and UV spectra indicated that ovalbumin amino acid residues microenvironment moved to polar environment.