| Pea protein isolate(PPI),as a by-product in the production of pea starch,is a plant-derived protein with high nutritional value and has the advantages of wide sources and low allergenicity.Emulsifying property is an important property of PPI.Due to the poor emulsifying property of natural PPI,it cannot meet the performance requirements of the food industry for highly emulsifying protein products.It is necessary to improve its emulsifying properties through appropriate modification methods.At present,the research on the improvement of PPI emulsifying property by modification treatment is not perfect,especially the understanding of the effect of extrusion and/or phosphorylation treatment on PPI emulsifying property and interfacial adsorption behavior is still insufficient.Therefore,on the basis of pre-experiment,this paper screened two modification methods of extrusion and phosphorylation to treat PPI,and studied the combined effect of the two,analyzed the changes of structural properties before and after PPI modification,and explored the mechanism of improving its emulsifying performance;PPI with different modification treatments was prepared into emulsions,and the effects of modification treatments on the interfacial properties and emulsifying properties of PPI were investigated.Finally,PPI with different modification treatments was used as an emulsifier in a commercially available almond beverage model system.The main research contents and results are as follows:Firstly,PPI was modified by extrusion,phosphorylation and extrusion combined with phosphorylation.After modification,the emulsifying activity index(EAI)of PPI was increased by 47.18%,42.69%,108.38%,respectively,and the emulsifying stability index(ESI)increased by 106.85%,61.65%,and 218.91%,respectively.Meanwhile,the changes in the structure and properties of PPI before and after modification were investigated.The results showed that under different modification conditions,the physicochemical properties of PPI had similar trends,and the effect of extrusion combined with phosphorylation treatments was the most significant.The extruded co-phosphorylated pea protein isolate(EPPPI)increased the exchange of sulfhydryldisulfide bonds,and the content of disulfide bonds was increased by 26.25%;exposed more hydrophobic groups,and the surface hydrophobicity was increased by 101.95%;the protein structure unfolded,the fluorescence intensity increased,and the maximum absorption wavelength was red-shifted;the secondary structure was changed,and some β-Turn were converted into β-sheets,in which the content of β-turn was reduced by 9.85%,while the content of β-sheets was increased by 15.06%;macromolecular aggregates were generated through hydrophobic bonds and disulfide bonds,and the particle size was increased by 49.60%.Subsequently,the effects of different modification treatments on the oil-water interface properties and emulsifying properties of PPI in the oil-in-water emulsion system were studied.The results showed that the interface properties and emulsifying properties of PPI were improved after modification treatment,and the improvement effect of EPPPI was the best.After extrusion combined with phosphorylation,the energy required for the adsorption of PPI to the oil-water interface decreased by 22.16%;the interfacial shear elastic modulus G’ and interfacial shear viscous modulus G’’ increased,and the viscoelasticity of the interface film was enhanced;the absolute value of the zeta-potential of the emulsion droplets was increased by 23.95%,and the particle size was reduced by 43.05%;the interface protein adsorption rate of the emulsion was increased by 19.00%,the interface protein content was increased by 15.93%,and the flocculation index was significantly reduced by 93.46%;the viscosity of the emulsion increased,the linear viscoelastic region was extended.In addition,the storage experiments and microstructure showed that the particle size distribution of the modified PPI emulsion was uniform.Moreover,the emulsion prepared by EPPPI only had a slight degree of droplet coalescence or flocculation after storage for 30 days,and the storage stability of the emulsion was significantly improved.Almond-based beverages were complex colloidal systems which were thermodynamically unstable and emulsifiers was needed to be added to suppress unstable conditions such as stratification,flocculation,and coalescence caused by protein precipitation and fat floating.Therefore,the effects of different modified PPI on the stability of almond beverages were explored.Compared with unmodified PPI,the storage stability of beverages prepared with modified PPI as emulsifier was significantly improved,and the improvement effect of EPPPI on beverages was closest to that of sodium caseinate(SC).After adding EPPPI,the protein adsorption rate at the beverage interface increased by 45.80%,indicating that it formed a multilayer film structure at the oil-water interface;the electrostatic repulsion between beverage droplets increased by 8.41%,and the particle size decreased by 37.13%;the centrifugal precipitation rate of the beverage was reduced by 22.66%,further indicating improved beverage stability.In addition,it could be seen from the storage experiments and micromorphological results that the beverage prepared by EPPPI had a uniform particle size distribution,good stability during storage,and a low degree of agglomeration,which was similar to the beverage prepared by SC as an emulsifier.The results of the study demonstrated that EPPPI had the potential to replace SC as an emulsifier in commercial almond beverages. |
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