Effect Of Heat Treatment On Structural And Functional Properties Of Peanut Protein Isolate And Its Application

In recent years,more attention has been drawn to the investigation of plant proteins in food and pharmaceutical fields,because plant proteins have distinct properties of oil-water（O/W）interfacial absorption,good emulsification and texture.Peanut protein isolate（PPI）is one of the most important plant proteins in nature,having abundant nutritional value and good features.In this paper,we studied the influence of heat treatment on structure,interface rheology and emulsifying properties of peanut protein isolate,and further studied the impact of different salt on the Pickering emulsion stability by PPI nanoparticles stabilized.Moreover,we utilized the peanut protein nanoparticles as a substitute for egg yolk（egg yolk powder or sodium caseinate）in salad dressing,and developed a new tofu sald dressing products.The present research provided a theoretical basis for the application of peanut protein isolate.The main results indicated as follows:（1）The effects of heat treatment at different temperatures on the structural and functional properties of peanut protein isolate were studied.70℃,80℃,90℃heat treatment induced the increase of protein size and surface hydrophobicity,the decrease of the protein zeta potential,especially at the temperature of 80℃（PPI-80）.The results of the secondary structure of the protein displayed that theβ-sheet structure of the protein decreased and the unordered coil increased.Especially in sample PPI-80,theβ-sheet structure decreased 17.4%and unordered coil increased 9.0%.The results of interface rheological and emulsifying properties indicated that the rate of adsorption on the oil-water interface,the elastic modulus and viscoelastic modulus of the adsorbed film raised.The emulsifying properties of PPI-80 also improved.Contrastingly,heat treatment at 90℃（PPI-90）revealed a slight increase in size,surface hydrophobicity and zeta potential versus PPI-80,which declared that long-term high temperature treatment may induce partial hydrolysis of protein aggregates.（2）The effects of salt on the transmittance（solubility）,surface potential zeta and their stabilized Pickering emulsions of the PPI nanoparticles.The results manifested that when Na Cl or Ca Cl₂ was added to the solution of PPI nanoparticles,the solubility reduced firstly and then heightened with the increase of salt concentration.The transmittance of PPI nanoparticles was 50.2%with 300m M Na Cl.While the PPI nanoparticles form precipitates and the transmittance decreases to 0 with the addition50m M and 100m M Ca Cl₂.Due to the effect of electrostatic shielding and ion crosslinking on salt ions,the surface potential zeta of the PPI nanoparticles solution is reduced.The consequences of the Pickering emulsions exhibited that the emulsion had more uniform distribution of particle size and better storage stability with different salt irons.It is worth noting that the emulsion particle size increased slightly with Na Cl of different concentrations,while the emulsion particle size rose significantly at different concentrations of Ca Cl₂.As a consequence,PPI nanoparticles stabilized Pickering emulsion has better resistance to Na Cl.（3）Preparation and evaluation of a novel salad dressing.The PPI nanoparticles mentioned above were stable with high concentration Na Cl and had excellent emulsifying properties.Therefor we exploited the PPI nanoparticles in salad dressing as a substitute for egg yolk（egg yolk powder or sodium caseinate）.A unique fermented bean curd was meanwhile used to development the new salad dressing.The outcomes represented that PPI nanoparticles can significantly improve the quality of the fermented bean curd salad dressing and reinforce its viscosity,especially when 0.5%PPI nanoparticles was added.The concret parameters were as follows:the hardeness was 14.81g,viscosity was162.1Pa.s,sensory evaluation was 40 points.