Study On The Diversified Modification Of Peanut Protein Isolates And Its Application In Different Fields

As a high-quality plant protein resource,peanut protein isolates（PPI）are widely used in the food industry because it is rich in a large number of essential amino acids.In addition to the food field,PPI has received widespread attention in the fields of medicine,materials,daily goods and additives due to its unique structural and functional properties.However,PPI is difficult to be used directly in different fields because of the limits on the natural structure and preparation conditions,which makes the diversified modification of PPI a hot topic of research in the protein field.In this thesis,we adopt diversified modification methods to improve or expand the characteristics and functions of PPI so as to provide a reference for maximizing the resource utilization of PPI:1)PPI was modified by synergistic treatment using various traditional methods（ultrasound,enzymes）,and the effect of the synergistic treatment on the structural and functional properties of PPI was investigated.The modified PPI was used as an additive to improve the quality of meatballs based on its improved functional properties.2)PPI was modified using an emerging nanoparticulation process.The carbon dots with good fluorescence detection were prepared with Cysteamine and PPI,and applied to the detection of Fe²⁺/Fe³⁺and lactoferrin（LF）content.3)PPI was nanofibrillated and investigated for its application in stabilizing high internal phase Pickering emulsions（HIPPEs）.The details of the study are as follows:（1）In addition to the significant reduction of particle size,molecular weight,surface hydrophobicity and orderliness of PPI,the synergistic ultrasound-enzymes treatment also had some effects on the hydrophobic amino acid content and the secondary structure of PPI.Meanwhile,the synergistic treatment also showed a positive effect on the functional properties of PPI.It is noteworthy that the solubility of PPI（U-P）treated by the synergistic Ultrasound-Papain treatment could be dramatically increased to 88%at p H=5.The emulsifying activity of PPI（U-N）treated by synergistic Ultrasound-Neutrase treatment could be significantly increased（143.97 m²/g）,and the foaming capacity of PPI（U-P）treated by synergistic Ultrasound-Papain treatment was increased to 65.00%.The above results indicated that the synergistic treatment can greatly improve the functional properties of PPI.Based on the positive effects of the synergistic treatment on the functional properties of PPI,we further used the synergistically treated PPI in the quality improvement of pork meatballs.The results showed that synergistic Ultrasound-Alcalase treatment and synergistic Ultrasound-Protamex treatment could both effectively improve the color,tissue status and overall acceptability of pork meatballs.（2）Protein has become a popular choice for carbon dots preparation in recent years due to the free amino and carboxyl groups.Based on the unique molecular structure of PPI,we used PPI and Cysteamine as precursors for the nanoparticle modification under high temperature and pressure.The prepared N,S-doped PPI carbon dots（N,S-PPI-CDs）exhibited intense blue fluorescence and good biocompatibility.We found that the obtained N,S-PPI-CDs exhibited good fluorescence response properties to Fe²⁺/Fe³⁺solutions within 30 s.The limit of detection（Lo D=0.21μM/0.17μM）was much lower than that reported in the literature,which implied that N,S-PPI-CDs can be used for the fluorescence detection of Fe²⁺/Fe³⁺.Considering the reversible binding property between LF and Fe²⁺/Fe³⁺,we further used it in the determination of LF content.The results showed that N,S-PPI-CDs exhibited high sensitivity（Lo D=1.92μg/m L）,and could be used for the quantitative determination of LF in LF supplements（recovery fluctuation less than 2.48%）.（3）Nanofibrillation of proteins is an emerging way of protein modification in recent years,and the obtained nanofibrils have attracted much attention in the food field due to their special fibrous structure.We modified PPI by fibrillation and explored the feasibility of the obtained nanofibrils for application in high internal phase Pickering emulsions.The results showed that the highest yields of nanofibrils were obtained by reacting at 90℃for 20 h.The results of gel electrophoresis,transmission electron microscopy（TEM）,Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）and contact angle showed that the molecular weight of PPI has significantly reduced due to hydrolysis.The diameter of the PPI nanofibrils was about 14 nm,and theβ-sheet content and crystallinity increased significantly compared with PPI,and the surface showed hydrophilicity.In the study of stabilization of HIPPEs,we found that the obtained nanofibrils could well stabilize HIPPEs when the fibrils concentration reached 0.9%（oil phase volume fraction of 75%）.Pickering emulsion showed solid-like behavior,and laser confocal microscopy and cryo-electron microscopy results showed that the oil droplets were tightly wrapped by the dense PPI nanofibrils(d_3,2=20.9±1.3μm),resulting in a significant increase in the stability of HIPPEs.