Preparation Of Egg White Protein Isolate-Curcumin Complex And Its Application In Emulsified Sausages

In recent years,with the improvement of people’s living standards,consumers have gradually realized the importance of a healthy diet,and fat substitutes have become a research hotspot in healthy meat products.Among them,protein-based fat substitutes have become excellent material for preparing fat substitutes due to their good amphipathic structure,good emulsifying activity,and the ability to carry hydrophobic functional factors.In order to optimize the fatty acid composition of emulsified sausages,vegetable oils are usually added to achieve healthy substitution.However,the presence of unsaturated bonds increases the incidence of oil oxidation.In addition,traditional fat substitutes do not have a solid texture similar to animal fat,which will affect the texture and quality of the product.Based on the above background,we chose egg white protein isolate（EPI）and curcumin（Cur）as the ingredients of fat substitutes,explored the optimal conditions for fabricating EPI-Cur complex using p H-shifting,and compared the effect of two treatment on the emulsified ability of EPI,including EPI-Cur complex and EPIp prepared by p H-shifting combined with heat treatment.Besides,the effect of curcumin on the oxidative stability of the emulsion when it is located in different phases of the emulsion was explored.Finally,based on these two protein emulsions,Curdlan was used to enhance the continuous phase of the emulsion,and an emulsion gel was constructed to replace the back fat in the emulsified sausages.The main research contents and results are as follows:1.Study on the construction of egg white protein isolate-curcumin complex and their Interaction MechanismCurcumin（Cur）is a class of phenolic substances with multifunctional properties,such as antioxidant,antibacterial,anti-inflammatory,and anti-tumor.However,its poor solubility and thermal stability at aqueous solutions limit its application in the food industry.In this study,egg white protein isolate（EPI）was complexed with curcumin via a p H-shifting method.The effects of ultimate p H（from p H 5.0 to p H 7.0）on the physicochemical properties of the complex were studied.Curcumin could reach 84.4%encapsulation efficiency at p H 6.0.Meanwhile,the curcumin retention rate of EPI-Cur was significantly increased at p H 7.0,80°C for 1 h,indicating that egg white protein isolate can effectively protect curcumin from thermal degradation.Compared with the original protein and free curcumin,the antioxidant capacity of EPI-Cur was significantly enhanced.The results of UV-visible spectroscopy and fluorescence spectroscopy indicated a static quenching in the binding with a strong affinity of 1.8×105 M^-1 at p H 6.0.In conclusion,the dispersion,thermal stability and antioxidant capacity of curcumin were improved by EPI nanocarrier made with p H shifting.The results provide a scientific theoretical basis for the application of curcumin in food,and gives an new ideas for the construction of egg white protein isolate nanocarriers.2.Effects of different treatment methods on emulsified properties of egg white protein isolateEmulsion is a thermodynamically unstable system.A good storage and oxidation stability of emulsion is a challenge for practical production.This study took egg white protein isolate-curcumin complex（EPI-Cur）as the research object,and compared the emulsified properties of protein between EPI-Cur and EPI nanoparticles（EPIp）constructed by p H-shifting combined heat treatment.Meanwhile,the antioxidant difference when the curcumin is in different phases of the emulsion was explored.The particle size and multiple light scattering results showed that the EPIp emulsion has the smallest particle size and TSI compared to the native EPI emulsion group.The laser confocal microscopic image indicated that the protein aggregation in the EPIp emulsion was significantly reduced and the oil droplets were smaller and more evenly distributed.The interfacial tension of the EPI treated by these two methods was significantly reduced and the kinetic parameters were increased compared with the native protein.Besides,we characterized the hydroperoxide and thiobarbituric acid value of the emulsion system after 12 days of storage at 60℃,and proved that when curcumin existed in the water phase,the PV and TBARs of EPI-Cur emulsion can be decreased by 43.0%and 29.8%respectively compared to emulsions stabilized by EPI.In summary,EPIp emulsion has the best stability,while EPI-Cur emulsion has the best oxidation resistance.Our research results provide a theoretical basis for the preparation of emulsions with both stability and oxidation resistance.3.Study on the application of antioxidant emulsion-based fat substitute in emulsified sausagesAfter the emulsion-based fat substitute replaces the back fat,the texture and oxidative stability of the emulsified sausages will be affected.In this study,the egg white protein isolate-curcumin complex stabilized emulsion（EPI-Cur）was used as the research object,and the emulsion gel（CEG）constructed after the continuous phase of the emulsion was strengthened with curdlan as the fat substitute control group.We explored the effect of the two 100%replacement of backfat on the physical and chemical properties,texture properties,fatty acid composition and lipid oxidation of emulsified sausages.Compared with the backfat group,the protein and water content of the emulsified sausages increased after the replacement of these two groups,and the total fat content could be reduced to6.2%;Compared with the pure water replacement group,EPI-Cur emulsion and emulsion gel replacement can increase the content of non-flowing water,thereby significantly reducing the cooking loss of the emulsified sausages.The color difference results showed that the brightness value L*and redness value a*of the emulsified sausages in the replacement group increased significantly,but the yellowness value b*did not change significantly.The saturated fatty acid content of the emulsion gel group is 21.3%lower than that of the backfat group,and the polyunsaturated fatty acid content was significantly increased;Besides,the addition of curcumin will inhibit the oxidation of oil caused by substitution.The antioxidant effect was strongest when curcumin was in the continuous phase of the emulsion in the form of a complex.In short,EPI-Cur emulsion has the best antioxidant properties as a fat substitute,but the emulsion gel replacement group can better maintain the original good texture of emulsified sausages.This study optimizes the shortcomings of traditional emulsions that are easy to oxidize as fat substitutes,and has positive guiding significance for the preparation of fat substitutes with antioxidant properties,water retention and excellent texture.