Study On High Internal Phase Emulsions Based On Pea Protein Isolate-EGCG-iron Ion Complexes For The Protection And Delivery Of β-carotene

Hydrophobic functional ingredientβ-carotene is a widely used natural pigment in the food industry.However,its poor water solubility and stability limit its function,therefore,it is urgent to design delivery system to improve its application performance.Oil-in-water emulsion is a simple and effective carrier for the protection of hydrophobic functional ingredients,and non-toxic amphiphilic biomacromolecule protein is an ideal emulsifier for the preparation of emulsion.Plant-based proteins,with their low-fat and low-calorie attributes,are increasingly favored by consumers.However,their inferior physicochemical properties limit their application in the food industry.Polyphenols can modify these plant proteins,and they can self-assemble to form a protein-polyphenol complex,serving as a more effective nutritional emulsifier.In addition,polyphenols rich in 1,2-dihydroxybenzene groups can bind to metal ions to form metal-polyphenol networks（MPNs）with high surface affinity and bioactivity.It is suggested that proteins,polyphenols and metal ions can form new composite materials with improved functional properties for the preparation of stable emulsion to deliver functional ingredients.Therefore,in this study,the complexes of pea protein isolate（PPI）with epigallocatechin-3-gallate（EGCG）and Fe³⁺were prepared.Firstly,the formation mechanism and application properties of the protein complexes were investigated,and their potential in emulsion preparation was confirmed.The PPI and its complexes were then used to prepareβ-carotene loaded high internal phase emulsions（HIPEs）,and their protective effects onβ-carotene were evaluated.The main research contents and results are as follows:（1）Interaction analysis and interface properties of PPI-EGCG complex:The PPI dispersion was obtained by p H-shift and heat treatment,and then PPI-EGCG non-covalent molecular complex was prepared under neutral conditions.Spectroscopy,calorimetry and molecular docking analysis demonstrated that the PPI-EGCG complex formed spontaneously.EGCG induced protein unfolding,the secondary structure of PPI changed fromα-helix toβ-sheet,and the molecular structure of PPI became disordered,resulting in a slight decrease in the thermal stability of the system.With the accretion of EGCG,the hydrophilicity of the complexes increased,which was beneficial to the function of protein,and the turbidity and particle size of the complex were gradually increased,indicating that the interaction between the PPI and EGCG was gradually enhanced.Optimization of the PPI-to-EGCG ratio led to the complexes having better foaming and emulsifying properties than the protein alone,especially when PPI:EGCG=10:1（w/w）.（2）Preparation and functional characterization of pea isolate protein-EGCG-iron ion ternary complexes:PPI-EGCG-Fe³⁺ternary complexes with different Fe³⁺mass fractions were prepared by molecular self-assembly.The interaction mechanism of the three was determined by microstructure observation,multi-spectral analysis and thermodynamic method.The physicochemical properties of PPI-EGCG-Fe³⁺complex were determined by particle size,potential,turbidity and surface hydrophobicity.The functional properties of PPI-EGCG complex and PPI-EGCG-Fe³⁺complex were compared,and the effect of Fe³⁺on the complex system was explained.It was found that PPI,EGCG and Fe³⁺could combine with each other via hydrogen bond,phenolic hydroxyl coordination bond and electrostatic interaction to form nano-network structure.The addition of Fe³⁺made the secondary structure of the protein become more disordered,decreased its thermal denaturation temperature and surface hydrophobicity,and increased its particle size and potential.The change effect was related to the amount of Fe³⁺.PPI-EGCG-Fe³⁺complex showed better interfacial properties,anti-oxidation and antibacterial properties,especially when EGCG:Fe³⁺=1:2（w/w）.（3）Study on the protective effect and bioaccessibility ofβ-carotene in high internal phase emulsions based on pea protein isolate complexes:HIPEs with 75%oil phase volume fraction were prepared with acidic and neutral PPI,PPI-EGCG,PPI-EGCG-Fe³⁺as emulsifiers and MCT as oil phase.The properties and stability of each emulsion were compared and analyzed.After loading the hydrophobic functional factorβ-carotene in the oil phase,the protective ability of the HIPEs to the active substance was evaluated.To investigate the digestive behavior of HIPEs and the bioaccessibility of embeddedβ-carotene by in vitro simulated digestion.It was found that acidic and neutral PPI,PPI-EGCG,PPI-EGCG-Fe³⁺can be used to form oil-in-water high internal phase emulsion（P-E,PE-E,PEFe-E）.Due to the network structure of PPI-EGCG-Fe³⁺complex,it can form a more compact and continuous interface on the droplet surface,thus improving the gel properties of PEFe-E,the stability of the embeddedβ-carotene under heat and light stress was also significantly improved.All HIPEs exhibited similar behaviors during digestion,which were destroyed gradually,and the emulsions prepared under acidic conditions were easier to be digested.The HIPEs system showed sustained release characteristics to the oil phase and could protect the internalβ-carotene,helping to improve its stability in the gastric environment.The neutral PPI-EGCG-Fe³⁺stabilized emulsion exhibited the best ability to improve the bioaccessibility ofβ-carotene.To sum up,this thesis has formed protein-polyphenol and protein-polyphenol-metal ion complexes based on pea protein isolate,defined the interaction mechanism between substances,and determined the functional properties of the complexes.It provides a new idea for the development of protein complex system.At the same time,the high internal phase emulsions based on protein and its complexes were developed for the protection and delivery ofβ-carotene,which improved the photothermal stability and bioaccessibility ofβ-carotene.It provides a new way for the application of hydrophobic functional ingredient in health food.