Self-Assembly Characteristics Of Pea Protein Isolate-High Methoxyl Pectin Complex Nanoparticles Prepared With Ultrasound

Pea protein is a high-quality plant protein with a relatively balanced amino acid composition,and rich in lysine.However,due to its strong surface hydrophobicity and low charge,pea protein has poor solubility and emulsification,which often results in instability in the system,limiting the application of pea protein in food.In addition,high methoxyl pectin can adsorb more on the surface of protein due to its low charge,it can be combined with proteins through hydrophobic and electrostatic interactions to provide steric hindrance effects to maintain the stability of protein systems.Therefore,in this study,protein-polysaccharide complex was used to prepare nanoparticles by self-assembly to stabilize protein system,and pea protein isolate(PPI)-high methoxyl pectin(HMP)complex nanoparticles were prepared by ultrasound.By studying the changes in physicochemical and structural properties of complex particles,the interaction between PPI and HMP and the self-assembly mechanism of PPI-HMP complex nanoparticles regulated by ultrasound were systematically explored;At the same time,through the study of the characteristics of emulsion stablized by PPI-HMP complex nanoparticles,the mechanism of ultrasonic control of PPI-HMP complex nanoparticles to form emulsion was clarified.The main research contents and results are as follows:(1)To establish method of PPI-HMP complex nanoparticles by ultrasound.PPI-HMP complex nanoparticles were investigated by characterizing turbidity,particle size,PDI,zeta-potential,emulsifying activity and stability.The results showed that PPI and HMP formed an insoluble complex at p H 3.0,existed in a co soluble state at p H 8.0,and formed a soluble complex at p H 2.0 and p H 6.0.At p H 2.0 and p H 6.0,the turbidity,particle size and PDI was low,emulsification activity and stability was good.Ultrasound can significantly reduce the turbidity,particle size and PDI of PPI-HMP complex particles.At p H 6.0,when the concentration of PPI-HMP complex nanoparticles was 8 mg/m L,PPI-HMP ratio was 1:1,the ultrasound time was 10 min,power was 5.43 W/cm~3,and temperature was 15°C,the complex nanoparticles had good emulsifying activity and stability.At p H 2.0,the concentration of PPI-HMP complex nanoparticles was 8 mg/m L,PPI-HMP ratio was 1:2,the ultrasound time was 5 min,power was 5.43 W/cm~3,and temperature was 25°C.The complex nanoparticles had good emulsifying activity and stability.(2)The self-assembly mechanism of PPI-HMP complex nanoparticles regulated by ultrasound was studied through microscopic and structural characterization.The results of Fourier transform infrared spectroscopy(FTIR),intrinsic fluorescence spectroscopy,and viscosity showed that,at p H 6.0 and 2.0,the addition of HMP resulted in rearrangement and refolding of the PPI structure,decreased exposure of tryptophan residues,increased ordered structure,decreased shear thinning rate,and increased viscosity.The hydrogen bonding,electrostatic,and hydrophobic interactions between PPI and HMP resulted in a tighter tertiary conformation of the complex nanoparticles with good storage stability.Ultrasound caused the secondary structure of PPI to fold to form a linear or helical structure,the protein structure unfolded and more groups exposed,the interaction between PPI and HMP was enhanced.The results of transmission electron microscopy(TEM)showed that PPI-HMP complex nanoparticles self-assembled at p H 6.0 and 2.0 to form a structure with uniform regular and orderly structure;At p H 6.0,ultrasound promotes the insertion of HMP molecular chains into the spherical structure of PPI;At p H 2.0,the lamellar structure of PPI is attached to the network structure of HMP,and ultrasound promotes the formation of PPI-HMP complex nanoparticle structures into spherical nanoparticles with a core-shell structure.(3)The mechanism of PPI-HMP complex nanoparticles by ultrasuond forming emulsion was studied.Through the study of the characteristics of emulsion stablized by PPI-HMP complex nanoparticles,the oil-water interface behavior showed that under p H 6.0and 2.0,the contact angle of PPI decreased with the addition of HMP,and the interfacial tension decreased rapidly and then stabilized with the increase of time.Ultrasound increased the hydrophilicity and interfacial tension of PPI-HMP complex nanoparticles,and the contact angle decreased.The storage results of emulsion showed that the particle size of emulsion stablized by PPI-HMP complex particle was larger,there were aggregates and the emulsion index was higher at p H 6.0.After the addition of HMP,the viscosity and Zeta-potential absolute values of emulsion stablized by PPI-HMP complex particle increased,the shear thinning rate and particle size decreased.The particle size did not change significantly during 15 days of storage,and there was no creaming phenomenon;Under p H 2.0,the particle size of emulsion stablized by PPI increased significantly when storage time was 1 d,which led to the phenomenon of creaming,the absolute value of zeta-potential decreased significantly.The emulsion stablized by PPI-HMP complex nanoparticle had higher viscosity and lower shear thinning rate.During 15 d of storage,the zeta-potential was relatively stable and there was no creaming phenomenon.After ultrasonic treatment,the shear thinning rate of emulsion stablized by PPI-HMP complex nanoparticle is reduced,and particle size is reduced,and the droplets are broken to form smaller dispersed droplets,which are more stable and have a longer shelf life.