Study On Graft Modification Of Perilla Protein And Construction Of Its Emulsion Delivery Systems

Food functional factors are a class of functional foods with specific physiological activities that are inseparable from the normal diet.With the rapid development of the food industry,food functional factors including vitamins,polyphenolic compounds,carotenoids,peptides and isoflavones have become popular all over the world.They have a wide range of roles in various aspects such as fertility,growth,regulation of metabolic processes,protection against oxidative stress,cardiovascular and gastrointestinal physiological disorders.However,most of the food functional factors are limited in market application due to their poor water solubility and susceptibility to unstable decomposition by light,heat and metal ions.In this thesis,perilla seed meal protein(PSMP)was used as raw material to investigate the effects of different modification methods on the structure and function of perilla protein.The inhibitory effect of caffeic acid(CA)on the harmful substances that may be produced by the glycosylation process was also studied,providing a theoretical basis and data support for the safety study of protein glycosylation products.Finally,modified products were used as an emulsifier forβ-carotene(BC)emulsions to study its stabilization and delivery in the emulsion delivery system.The main research contents and results were follows:(1)PSMP-polyphenol covalent conjugates were prepared by oxidative modification of perilla seed meal protein(PSMP)with gallic acid(GA),protocatechuic acid(PCA),caffeic acid(CA),apigenin(API)and luteolin(LU)induced by alkali method.The covalent conjugates were characterized and tested,and the results showed that the PSMP-flavonoid covalent conjugates had the highest total p H enolic binding rate with increased free amino content compared to PSMP,while the PSMP-p H enolic acid covalent conjugates experienced a decrease in free amino content.Gel chromatograph y showed a shift in the protein molecular weight bands and oxidative modification resulting in a decrease in the content ofα-helices and an increase in irregular curl in the covalent conjugates except for PSMP-PCA.The turbidity and hydrophobicity analysis revealed that the turbidity of the polyphenol-modified covalent conjugates increased and the hydrophobicity decreased except for PSMP-GA.(2)Based on the structural changes of PSMP-polyphenol covalent conjugates compared to PSMP,the functional properties of different PSMP-polyphenol covalent conjugates were investigated,and their application in emulsion delivery systems was also studied.Differential Scanning Calorimeter(DSC)measurements revealed that the denaturation temperature(T_p)of PSMP modified by phenolic acids was significantly higher,while the peak melting temperature(T_p)of PSMP modified by flavonoids was lower than that of PSMP.Under UV and heating treatments,each PSMP-polyphenol covalent conjugate showed higher stability compared to PSMP,with reduced particle size of the emulsion,increased absolute value of the potential,and increased retention ofβ-carotene in the emulsion.(3)In view of the ability of PSMP to covalently bind to small polyphenols to improve protein structure and properties,the effects of different molecular weight sugars on the structural and functional properties of the glycosylated products of perilla protein were further investigated:fructose(FRU),dextran(DEX)and maltodextrin(MD)were used to modify PSMP by glycosylation,and the fourier infrared spectra(FTIR)and endogenous fluorescence spectra revealed that the secondary and tertiary structures of each glycosylated product The IR and endogenous fluorescence spectra revealed changes in the secondary and tertiary structures of each glycosylation product,with P-DEX undergoing the largest blue shiftΔ17 nm and the greatest fluorescence quenching.The results of DSC and Scanning Electron Microscope(SEM)also demonstrated that the modification of PSMP glycosylation led to the improvement of its structure and properties.(4)Since some intermediate by-products or harmful substances might occur in the glycosylation process,the intermediate products and end harmful substances in the glycosylation process were examined,and the effect of CA addition on the glycosylation products was investigated.The results showed that some intermediate products and harmful substances were generated in the protein glycosylation process,but the addition of CA would have a strong inhibitory effect on fructosamine,Methylglyoxal(MGO)and advanced glycation end products(AGEs).Among them,perilla protein-dextran-caffeic acid(P-D-CA)had the best inhibitory effect,with 87.91%and 81.03%inhibition of N~ε-hydroxymethyl lysine(CML)and N~ε-hydroxyethyl lysine(CEL),respectively.(5)Based on the modified products obtained from the above-mentioned different modifications of perilla protein,BC emulsions were prepared using PSMP and each different modification product(perilla protein-caffeic acid conjugate(P-CA),perilla protein-dextran glycosylation product(P-D)and P-D-CA)as emulsifiers,respectively.The stabilization effect of different emulsifiers on BC emulsions was also investigated,and it was found that P-D-CA emulsions had the highest retention of BC after UV and heat treatment.