Study On The Construction Of Composite Nanostructures And Stability Of Emulsions Using Rice Proteins And Cod Proteins

Rice proteins(RPs)are recognized as high-quality plant proteins with high nutritional value and low allergenicity.However,due to the existence of a large number of disulfide groups and hydrophobic interactions,RPs have poor solubility of and low commercialization levels.However,the conventional physical,chemical,and enzymatic modification methods improving the solubility of RPs have the disadvantages of incomplete molecules,high price,poor controllability,complicated operation,and low yield.In this study,hydrophilic co-assemblies(CRPs)of rice proteins(RPs)and cod proteins(CPs)were prepared by non-covalent modification by the p H-cycle technology,and their construction mechanism and solubilization mechanism were explored.Stable Pickering emulsions were prepared by synergistic stabilization of CRPs and starch nanocrystals(SNCs).The binding mechanism between CRPs and SNCs was explored,and the stability of the Pickering emulsions during long-term storage was characterized.This study aims to provide conceptual and theoretical basis for the application of RPs in food science and other fields.The specific research contents are as follows:Firstly,the hydrophilic co-assemblies(CRPs)were prepared by RPs and CPs,and the mechanisms for assembling and stabilizing CRPs were explored.RPs and CPs were deprotonated at p H 12.0 to form stable"molten globules"unfolded structures.Binary complexed CRPs were prepared by slowly adjusting to neutral p H.After p H-cycle,the solubility of RPs was increased by 54 times,reaching 92.7%at the RPs/CPs mass ratio of 1:1.The results of microscopic observation and hydrodynamic radius showed that the CRPs were nanoparticles with a radius of 80?150 nm.SDS-PAGE results showed that p H cycle did not alter the primary structure of the proteins.Microscopic observation,fluorescence spectrum,and far-UV circular dichroism spectrum showed that the interactions of the two proteins were driven by hydrophobicity,leading to sheet-helix transition,and formed acid resistant co-folded microstructures.In addition,decreased surface hydrophobicity and increased zeta-potential were the main reasons for the good water solubility of CRPs.Secondly,the functional,nutritional,and digestive characteristics of CRPs were studied.The emulsification activity index of CRPs was increased from 3.3 m~2/g to 16.0 m~2/g.CPRs were rich in essential amino acids,which were much higher than the recommended intake regulated by the Food and Agriculture Organization of the United Nations(FAO)and the World Health Organization(WHO).Meanwhile,the Lys content in CRPs was increased from 3.2g/100 g protein to 5.5 g/100 g protin,which solved the problem of Lys deficiency in RPs.Moreover,SDS-PAGE results showed that p H cycle improved the digestibility of myosin in CPs.Therefore,the prepared CRPs was a new type of proteins with rich and reasonable amino acid compositions and excellent digestibility.Afterwards,the binding mechanism between CRPs and SNCs was studied.Fluorescence spectra showed that the binding of CRPs to SNCs induced static quenching of the intrinsic fluorescence of CRPs.Isothermal titration calorimeter(ITC)results showed that the binding process was an exothermic process driven by van der Waals force and hydrogen bonding.Interfacial tension,three-phase contact angle,and cryo-scanning electron microscopy confirmed that CRPs@SNCs had good mechanical properties,and based on amphiphilic properties of CRPs,they can synergistically stabilize Pickering emulsions.Finally,the stability Pickering emulsions stabilized by CRPs@SNCs was studied.The O/W type Pickering emulsion were prepared at a total CRPs@SNCs concentration of 2.0%(w/v)and oil fraction of 0.6 at p H 7.0.The results of emulsification activity index(EAI)showed that the SNCs reduced the emulsification activity of CRPs but improved the stability of the emulsions.Creaming index(CI),microscopic observation,and droplet size analysis showed that CRPs and SNCs synergistically formd and stabilized uniform Pickering emulsions by delicately controlling the mass ratio between CRPs and SNCs.When the ratio of CRPs/SNCs=1:1(w/w),the particle size remained unchanged in the tested long-term storage for up to 28days.In conclusion,CRPs prepared by the p H-cycle technology had excellent water solubility,reasonable and rich amino acid compositions,and good digestion and functional characteristics.By interacting with SNCs,the mechanical strength of CRPs could be improved,and the O/W type Pickering emulsions can be stabilized synergistically.This thesis provided a new non-destructive approach for solubilization and commercial utilization of RPs,which provided a theoretical basis for enriching the practical applications of RPs.