| In recent years,emulsions have been widely used in food,beverage and pharmaceutical industries.The emulsion can not only embed non-water-soluble substances in it to improve its bioavailability,but also has good stability and can be used to extend the shelf life of commodities.Egg white protein has abundant production and extensive resources.Compared with other dairy products,its amino acid composition is the closest to the amino acid pattern of human protein.It has extremely high nutritional value and good functional properties.At present,food-grade Pickering particles were mainly prepared from raw materials such as whey protein and soy protein isolate.Egg white protein was rarely used as an emulsifier/stabilizer in emulsion systems.In this study,egg white protein was used as the raw material,and ultrasonic combined with transglutaminase(Glutamine transaminase,TG enzyme)was used to modify the egg white protein.Then egg white protein gel particles(EWP-GP)were prepared by high-pressure homogenization technology.EWP-GP and chitosan were used as emulsion stabilizers to prepare egg white protein Pickering emulsion and egg white protein-chitosan double emulsion.And the changes in thermal stability,in vitro digestibility and storage stability of ?-carotene in three emulsions(single-layer emulsion,mixed emulsion,and double-layer emulsion)were explored.The main research results and conclusions were as follows:(1)EWP-GP was prepared by thermal gel method,and the effects of ultrasonic power and TG enzyme treatment on the surface characteristics of EWP-GP were investigated.With the increase of ultrasonic power,the particle size was firstly decreased and then raised.The minimum particle size of EWP-GP prepared by ultrasonic(240 W)-TG enzyme was 287 nm.The particle size of EWP-GP with 360 W ultrasonic power was 412 nm,while that of ordinary EWP-GP was 435 nm.The absolute values of Zeta-potential of EWP-GP prepared under the three conditions were all greater than 30 m V,showing good electrostatic stability.Turbidity test showed that hydrogen bond was the main force maintaining EWP-GP,which was dominant among all the forces.The results of fluorescence spectra and the three-phase contact angle showed that the EWP-GP modified by 240 W ultrasonic and TG enzyme had good surface hydrophobicity and wettability.Under this condition,the emulsification of the prepared particles was 73.5%,while that of the ordinary EWP-GP was 40.2%,which was 82.8% higher than that of the blank.Therefore,240 W ultrasonic power treatment for10 min combined with TG enzyme modification is an effective way to prepare EWP-GP,and the particles prepared under this condition are suitable for the production of Pickering emulsion.(2)Pickering emulsion was prepared with EWP-GP as emulsion stabilizer,and the effects of EWP-GP concentration and oil phase ratio on the properties of Pickering emulsion were investigated.The particle size of the emulsion decreased with the increase of EWP-GP concentration When the oil phase ratio was increased,resulting in the larger particle size and surface potential of the emulsion.while the emulsion segregation index was decreased.When the oil phase ratio was 20%,the emulsion particle size was 28.1?m,and the emulsion segregation index was 51.6%.When the oil phase ratio was 40%,the emulsion particle size was 47.4?m,and the emulsion segregation index was 14.2%.The centrifugal stability of the emulsion increased with the increase of EWP-GP concentration,but decreased with the increase of oil phase ratio.In summary,when the concentration of EWP-GP was 4% and the volume fraction of oil phase was 40%,the Pickering of egg white protein had better emulsion characteristics.On the basis of egg white protein Pickering emulsion,egg white protein-chitosan bilayer emulsion was prepared by layer-by-layer self-assembly technology,and the effect of chitosan concentration on bilayer emulsion was explored.When the p H value of the solution was 6,the surface potential of EWP-GP and chitosan was opposite,and the absolute value of the potential was greater than 10 m V,which is the optimal preparation condition for the double emulsion.With the increase of chitosan concentration,the particle size of the double emulsion increased significantly,and the surface potential of the emulsion changed from negative to positive.When the concentration of chitosan was 0.6%,the surface potential of the double emulsion approached 0,indicating that chitosan molecules formed a double-layer emulsion on the surface of Pickering emulsion by electrostatic attraction.The apparent viscosity of the double-layer emulsion shows a decreasing trend with the increase of the shear rate,that is,it shows the phenomenon of shear dilution,which is consistent with the characteristics of non-Newtonian fluids.Moreover,the G' of the emulsion was always higher than G'',and there was no crossover between these two values,indicating that a gel network structure dominated by elasticity was formed in the emulsion.(3)EWP-GP and chitosan were used as emulsion stabilizers,and the single emulsion,mixed emulsion and double emulsion loaded with ?-carotene were prepared.The stability changes of ?-carotene in three emulsions(single emulsion,mixed emulsion and double emulsion)were investigated.The particle size of single-layer emulsion and mixed emulsion changed significantly after heat treatment,and the retention rate of ?-carotene decreased significantly.However,there was no significant changes in the particle size of double-layer emulsion after heat treatment for 30 min at 20 ? 60 °C,and the retention rate of ?-carotene of double-layer emulsion was still as high as 74% at 80 °C.In the process of in vitro digestion,the double emulsion could maintain the emulsion structure,while the demulsification of mixed emulsion and single emulsion appeared at 90 min and 120 min,respectively.The bioavailability of ?-carotene in the three emulsions were as follows double emulsion(40.2%)> single emulsion(34.3%)> mixed emulsion(25.5%).Within 15 days of storage,the particle sizes of the three emulsions were significantly increased,and increased by 27.9%,30.2% and 16.1%,respectively,compared with that of fresh emulsion.The double-layer emulsion had the best protective effect on ?-carrot and oil.After 15 days of storage,the retention rate of ?-carotene reached 50.3%,and the POV value of oil in the emulsion was 39.3 meq/Kg.The results showed that the double-layer emulsion had good thermal stability,anti-digestion stability and storage stability. |
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