Research On Oxidative Decolorization Of Zein And Its Application As Coating In Duck Egg Preservation

Zein exhibits excellent water vapor and oxygen barrier properties after being coated.Moreover,its ability to decompose via proteases in the human body and microorganisms in the intestinal tract makes it a promising material for creating edible packaging.However,the presence of yellow pigment in common Zein limits its application in food preservation.Duck eggs are a traditional poultry product in China,and their high moisture content and susceptibility to microorganisms make them prone to deterioration during storage,transportation,and sales.Thus,this paper focuses on the preservation technology of Zein,including oxidation decolorization,Zein ethanol-based blend coating,and Zein water-based nanoparticle coating,with the aim of clarifying the preservation effect and mechanism of Zein on duck eggs.This research seeks to provide theoretical support for expanding the high-value utilization of corn processing by-products and innovating the green preservation of poultry eggs and their products.（1）Zein was treated with hydrogen peroxide to investigate the effects of treatment time,hydrogen peroxide concentration,and Zein concentration on decolorization and protein retention in Zein ethanol solution.The optimization of the hydrogen peroxide decolorization process of Zein was based on a response surface test.Physicochemical properties of proteins were analyzed,and the film-forming properties of Zein were compared before and after decolorization to clarify the effect of the oxidant on protein quality.Results showed that the decolorization efficiency of hydrogen peroxide increased significantly with an increase in treatment time and concentration of hydrogen peroxide,while the protein retention rate decreased.On the other hand,with an increase in Zein concentration,the decolorization efficiency of hydrogen peroxide decreased significantly,and the protein retention rate increased.The optimal decolorization process of hydrogen peroxide was determined as follows:hydrogen peroxide concentration at 4.51%,treatment time at 12 hours,and Zein concentration at3%.Under these conditions,the pigment removal rate of Zein was 60.53%,and the protein retention rate was 88.56%.Decolorized Zein film has improved color and oxygen resistance,while mechanical properties and water resistance were reduced by less than 20%.The molecular weight of Zein remained unchanged after treatment,but theα-helix content decreased while theβ-fold content increased.The solubility of Zein decreased from 83.11%to 75.59%,surface hydrophobicity decreased from 1598.40 to1493.20,and the content of free sulfhydryl groups decreased from 6.49μmol/g to 0.99μmol/g.In conclusion,hydrogen peroxide can effectively reduce the content of yellow pigment in Zein solution while maintaining the quantity of Zein.Films prepared with decolorized Zein have a lighter color and better oxygen resistance,with only a slight reduction in mechanical strength and water resistance.（2）Fresh duck eggs were coated with Zein ethanol-based blend and traditional wax,and their preservation effects were compared and analyzed.The number of Zein coating layers was optimized based on preservation effect and cost.The preservation mechanism of duck eggs by Zein ethanol-based blending coating was analyzed by improving eggshell morphology and strength through coating treatment and regulating physicochemical properties of duck egg white.Results showed that during 60 days of storage,the Zein coated group effectively controlled the p H range of duck egg white（8.80～9.06）compared to the uncoated group（p H range of 8.80～9.51）,and slowed down the decrease of Haugh unit and Yolk Index（21.26 and 0.15 respectively）,while the uncoated group experienced a greater decrease in these parameters（30.83 and 0.22,respectively）.The preservation effect of Zein coating was not inferior to that of wax coating used in large-scale industrial applications.Two layers of Zein coating improved the preservation effect of duck eggs,while three layers did not have a significant impact.Additionally,coating treatment enhanced eggshell strength and surface density,slowed down water loss in duck egg white,with A₂₁ and A₂₃ decreasing and A₂₂ increasing,slowed the transition rate of duck egg white from ordered to disordered structure and reduced the increase in free sulfhydryl content.In conclusion,Zein ethanol-based coating has similar preservation effects as wax coatings,and two layers of Zein coating can achieve a balance between preservation effect and raw material cost.The coating improves eggshell strength,slows down water loss in duck egg white,and maintains the stability of egg white structure,resulting in good preservation effects for duck eggs.（3）Zein/chitosan（CS）composite nanoparticles were produced using a anti-solvent method,with the Zein/CS mass ratio optimized based on storage stability and redispersibility.Fresh duck eggs were coated with the Zein/CS nanoparticle aqueous dispersion solution and a direct blend solution,and the quality difference during storage was analyzed.The advantages and mechanism of the composite nanoparticle aqueous dispersion solution coating in maintaining the freshness of duck eggs were identified.Results revealed that Zein/CS nanoparticles prepared with the optimal mass ratio exhibited better stability and redispersibility during low-temperature storage.The formation process of Zein/CS nanoparticles mainly involved hydrogen bonding,hydrophobic interaction,and electrostatic interaction between Zein and CS.During the35-day storage test,compared to the uncoated group,the coated groups demonstrated effective control of p H values of duck egg whites and reduced decline of Haugh unit and Yolk Index of duck eggs.The coated groups also formed a dense and uniform film on the eggshell,improving barrier performance.Furthermore,nanoparticles enhanced the surface hydrophobicity and optical properties of the coating,resulting in higher contact angle and light transmittance.However,the barrier performance of the nano coating was not significantly different from that of the blend coating.In conclusion,the optimal Zein/CS mass ratio is 5:1,and the composite nanoparticles exhibit better stability and redispersibility under low-temperature storage.The preservation effect of the Zein aqueous nanoparticle dispersion coating is not significantly different from that of the blend coating but has the advantage of a convenient and safe coating.Nanoparticles improve the surface hydrophobicity and optical properties of the coating,enhancing barrier performance.