| Emulsification is one of the most important functional properties of food proteins.Small molecule surfactants have been proved to have important effects on the stability of protein emulsions through interface competition.At present,studies are usually limited to the analysis of the effect of surfactant types and surfactant-protein concentration ratio on the interfacial substitution efficiency,without further exploring the rule of protein itself on surfactant substitution efficiency.In this study,peanut mass protein was taken as the research object,two different types of coarse and fine emulsions were prepared separately to study the interface substitution rules of Tween20 on different types of peanut protein(including peanut protein,arachin,conarachin and peanut heat-modified arachin)and the stability of the emulsion.The main research results are as follows:(1)By single factor and orthogonal experiment,the optimum preparation conditions of peanut protein coarse emulsion were compared:the content of peanut mass protein 0.6%,oil volume fraction 15%and shearing time 2.5min.Peanut protein was separated by ammonium sulfate deposition method to obtain arachin and conarachin.Comparing the emulsifying properties of the three peanut proteins,it was found that the flocculation and coalescence index of the conarachin emusion was the lowest,the aggregated particles of it were the least,the interface adsorption concentration of it was the highest,and the emulsifying stability of it was better than that of peanut protein and arachin.(2)In crude emulsion system,The interfacial substitution rate of Tween 20 for peanut crude protein increased first and then decreased with the increase of Tween 20concentration.When the Tween 20 content is 1%,the interfacial adsorptive protein concentration(Γvalue)minimum of 5.25 mg/m~2.Under the conditions of oscillation time 0.5h,pH 9.0,and ionic strength 0.1-0.5mol/L,the highest substitution rate of peanut interfacial protein reached 69%.Compared with the Tween 20 containing crude peanut emulsion,the Tween 20 emulsion was more stable.After 6d storage,the Tween20 emulsion had emulsification but no oil production phenomenon.(3)In fine emulsion system,when the Tween 20 content is 0.5%,the oscillation time is 1 h,the minimumΓvalue of peanut emulsion is 6.22 mg/m~2,The highest substitution rate of interfacial proteins is 61%.The particle size of peanut protein micro emulsion without Tween 20 began to increase rapidly after 60h storage,while the particle size of emulsion sample with Tween 20 changed little during storage.During the 20d storage period,the milk index of the former increased significantly with the extension of time,while the latter did not appear the milk phenomenon.(4)The structure of peanut protein micro emulsion was observed by laser confocal scanning microscope(CLSM).It was found that compared with the emulsion samples without Tween 20,the emulsion containing Tween 20 had smaller particle size and thinner protein layer at the oil droplet interface,indicating that a large amount of peanut protein at the interface had been replaced by Tween 20.The oil droplets of the two emulsions flocculated to different degrees with the storage time.(5)Compared with the crude peanut protein,the Tween 20 shows weaker interfacial substitution between the two components of peanut protein in the micro emulsion.When the Tween 20 content is 1%,the highest substitution rate of arachin is42%and the lowest interphase protein concentration is 7.35mg/m~2.The highest replacement rate of conarachin is 34%,and the lowest interfacial concentration of it is9.36mg/m~2.Under the same conditions,the effect of Tween 20 displacing the arachin is greater than the effect of Tween 20 displacing the conarachin.Results of SDS-PAGE showed that after Tween 20 treatment,the subunit bands of interfacial arachin and conarachin in the emulsion were significantly lighter than those in the emulsion without Tween 20,but the subunit composition did not change significantly.(6)The results of stability of the two peanut protein components in the micro emulsion storage showed that the arachin micro emulsion without Tween 20 was unstable and the emulsion appeared quickly,while the conarachin micro emulsion containing Tween 20 did not appear in the storage period of 20d.For the companion conarachin micro emulsion,emulsion did not appear during the storage period whether adding Tween 20 or not.(7)After moderate thermal modification of arachin to make micro emulsion,it was found that the surface hydrophobicity of the protein had a significant effect on the interfacial substitution ability of Tween 20.After heating treatment for 15min,the Tween 20 interfacial substitution rate was only 19%,while after heating treatment for45min,the highest interfacial substitution rate was 91%.(8)The results of stability of thermally modified arachin micro emulsion during storage showed that in the Tween 20 sample emulsion,the emulsion of the thermally modified sample at 15min showed have no emulsion during the whole storage period,while the emulsion of the thermally modified sample at 30min and 45min showed have emulsion instability after storage for more than 5 days.The results showed that moderate substitution of Tween 20 for the interfacial protein enhanced the stability of the emulsion,but if it was excessive substitution,it would reduce the stability of the emulsion. |
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