The Preparation,Properties Of Glycated Egg White Protein And Its Application In Nanoparticles

Hen egg white is a very important food industry ingredient,which has an important impact on the nutrition,texture and flavor of food.However,egg white protein(EWP)in the egg white powders showed a poor functional properties after spray-drying compared to fresh egg white.Therefore,how to improve the functional properties of EWP by using safe modification means is particularly important.In this thesis,EWP was used as the raw material,modification of EWP was carried out by dry-heating glycation using low molecular weight sugars.The relationships between structural changes and improvement of functional properties were investigated by understanding the effects of glycation on structure,physicochemical properties and functional properties of EWP.The mechanism by which glycation improved the functional properties of EWP was revealed.This study provides systematic theoretical guidance for EWP glycation modification technology,and provides useful information for the development of egg white powders with special high-properties and expanding industrial applications of EWP.The detailed results were depicted as below:1)Four low molecular weight sugars: fructo-oligosaccharide(FO),isomalto-oligosaccharide(IMO),resistant maltodextrin(RMD)and maltodextrin(MD)were used to perform the glycation of EWP through dry-heating Maillard reaction(at 60? and relative humidity of 79%).The solubility,grafting degree,browning degree,color change and amino acid composition of the four sugar-protein conjugates were investigated,respectively.And the physicochemical properties and their functional properties were also examined.The results showed that EWP glycated with IMO showed a higher grafting degree and better gelling and emulsifying properties.The IMO-EWP conjugates were selected to further investigate the effect of glycation on the structure of EWP.Sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE)showed that glycation increased the relative molecular weight of EWP,and promoted cross-linking between protein molecules.The glycoprotein staining verified the grafting of IMOs to EWPs.The liquid chromatography-mass spectrometry(LC-MS)indicated that the mass-to-charge ratios of the EWP have significantly changed after glycation;the primary product of the Maillard reaction-Schiff Base was detected by Fourier transform infrared spectroscopy(FTIR).Besides,intramolecular and intermolecular ?-sheets increased,while the content of the 310-helix structure decreased after glycation of EWP.2)In order to investigate the emulsifying properties of glycated EWP,the glycation product IMO-EWP was prepared by IMO and EWP through dry-heating Maillard reaction for 3 days,and the characteristics of emulsions prepared with IMO-EWP under mild pH(6.0-7.0)were investigated.The results showed that the surface hydrophobicity of IMO-EWP was higher than that of EWP.The particle size of IMO-EWP emulsion was smaller than that of original EWP,the ?-potential and the protein content at interface were significantly higher than those of EWP emulsion.The physical and chemical stability of the emulsion was also investigated.Compared with EWP,the oxidative stability of the IMO-EWP emulsion was improved due to the enhanced DPPH and ABTS radical scavenging activities;the storage and thermal stabilities and salt tolerance of the emulsions prepared with IMO-EWP were significantly stronger than those of emulsions prepared by EWP.The physical stability of the emulsion was greatly affected by pH.The stability of the emulsion increased with the increasing pH,and the IMO-EWP emulsion prepared at pH 6.0 had poor thermal stability.Furthermore,the rheological properties of IMO-EWP emulsions were highly dependent on protein concentration and oil content.3)IMO-EWP was employed to study the changes of gelling properties and intermolecular forces involved in the heat-induced gel formation after glycation modification.The rheological behaviors indicated that it took less time to form the heat-induced IMO-EWP gels with the extension of glycation time.The intermolecular forces involved in the formation of EWP gel were also affected by glycation,where hydrogen bonds and hydrophobic interactions significantly increased while disulfide bonds decreased.The fracture strength,bound water relaxation proportion and water-holding capacity(WHC)of the IMO-EWP gels were significantly enhanced.A positive correlation existed in the WHC and gel fracture strength.The scanning electron microscope pictures of the IMO-EWP gel showed a finer three-dimensional network structure.The changes of intermolecular forces after glycation resulted in a fine network structure of EWP gel,which significantly enhanced the fracture strength,bound water proportion and WHC of the gel.4)Since the poor thermal stability of EWP,it remains challenges to prepare nanoparticles for EWP above the denaturation temperature at neutral conditions.In this section,the effects of protein concentration,temperature,pH,ionic strength and grafting degree(DG)on the thermal aggregation behaviors of IMO-EWP conjugates were studied.And the nanoparticles were fabricated from IMO-EWP conjugates by heating at 90? for 30 min.To further reveal the formation mechanism of nanoparticles,the structures,thermal denaturation properties and surface properties were compared between the EWP and IMO-EWP conjugates.Glycation improved the thermal stability and surface net negative charges of EWP due to the change of EWP structure.The thermal aggregation of EWP was inhibited by glycation and the inhibition was enhanced with the higher DG.Meanwhile,the produced nanoparticles were < 200 nm in size at pH 3.0,7.0 and 9.0 in the presence of NaCl.The increased thermal stability and surface net negative charges after glycation contribute to the inhibition.5)To investigate the potential of heat-induced nanoparticles as stabilizer for oil-in-water emulsions,the IMO-EWP nanoparticles(HIN)were prepared by heating IMO-EWP conjugates at 90? for 30 min at pH 6.0-9.0,and the properties of the prepared emulsions were investigated.Compared to the heat-induced EWP aggregates(HEA),HIN has a smaller particle size(< 100 nm)and more surface hydrophobic groups and net charges.The particle sizes of the emulsions prepared by HIN were smaller and more uniform than those of the other EWP emulsions.As compared with IMO-EWP and EWP,the HIN prepared emulsion has the highest protein adsorption capacity at the oil-water interface resulting in a dense interfacial layer on the oil droplet surface.The stabilities of the emulsions at pH 6.0-9.0 was evaluated by measuring storage(1-28 days),oxidation (during storage for 28 days),heat(90? for 30 min)and salt(0-150 mM NaCl)stabilities.The results revealed that the HIN-stabilized emulsions exhibited higher oxidative stability and were stable against droplet aggregation with slightly increased diameters at pH 6.0-9.0.Moreover,the emulsions stabilized by thermostable IMO-EWP and HIN showed good heat stability at pH 7.0-9.0 and high tolerance to 150 mM NaCl.In conclusion,the HIN-stabilized emulsions exhibited the best physicochemical stability among the modified EWPs(IMO-EWP and HEA).These findings may have important implications for the fabrication of EWP-based emulsions.