Construction And Application Of Modified Pea Protein-based High Internal Phase Emulsion

Bioactive compounds have attracted much attention for their remarkable health benefits,such as antioxidant,anticancer,anti-inflammatory,and anti-aging properties.However,these active ingredients often have problems of poor environmental stability and low bioavailability during the application process,so they usually need to be added to food through the delivery systems.Food proteins are widely used as carriers for the delivery of bioactive nutrients because of their high nutritional value and recognized as safety.Among them,pea protein has attracted much attention due to its high nutritional value,low production cost,low allergenicity,non-transgenic status,and wide availability.However,compared with the animal protein,pea protein has poor functional properties,which limits its application in the delivery systems.To improve the functional properties of pea protein,on the one hand,the functional properties of a protein can be enhanced by non-thermal physical modification;On the other hand,the ability of the protein to stabilize an emulsion can also be improved by enhancing the interaction between the protein and polysaccharides.Therefore,in this study,pea protein isolate(PPI)was selected as the main raw material.Firstly,it was used to improve the stability and emulsifying property of PPI as the carrier matrix through combined physical modification.Then,the interaction between the modified PPI and the polysaccharide sodium alginate(SA)was investigated,and the modified PPI-SA complex was used to stabilize the high internal phase emulsion for food 3D printing.Finally,the high internal phase W/O/W double emulsion was constructed to realize the co-delivery of hydrophilic and hydrophobic functional nutrients.The main research contents and results are as follows:(1)Study on physical modification and functional properties of PPI: The effects of highpressure homogenization,ultrasonic treatment,combined treatment,and different combined treatment sequences on the structure and function of PPI were investigated.The effects of different treatments on the structure of PPI were analyzed by particle size distribution,microstructure,surface hydrophobicity,intrinsic fluorescence spectrum,UV-vis absorption spectrum,and circular dichroism spectrum.The effects of different treatments on PPI function were evaluated by solubility,foaming,and emulsifying properties.The results showed that high-pressure homogenization or ultrasonic treatment promoted PPI insoluble suspension to become uniform protein dispersion through cavitation effect,high shear force,and turbulence,so that the particle size of PPI was greatly reduced,the space structure was expanded,the hydrophobic amino acid residues were exposed more,and the surface hydrophobicity was obviously improved.The structure affects the function,and the solubility,foaming ability,and emulsifying activity of the modified PPI were improved greatly.In addition,the combined treatment had a further effect on the protein properties,which was largely dependent on the post-treatment step.The combined treatment group with high-pressure homogenization followed by ultrasound(HU-PPI)showed the best functional properties.(2)High internal phase Pickering emulsion(HIPPEs)based on modified PPI-SA complex and its application in food 3D printing: The HU-PPI-SA complex was prepared by simple molecular self-assembly,and the interaction between protein and polysaccharide was analyzed.A PPI-SA complex stable high internal phase Pickering emulsion was constructed,and its feasibility for food 3D printing was evaluated.The results showed that the formation of the HU-PPI-SA complex was confirmed by particle size change and scanning electron microscopy.The interaction between HU-PPI and SA mainly occurred through electrostatic interaction and hydrogen bonding.A higher concentration of SA(≥ 0.5 wt%)would change the secondary structure of HU-PPI and make it looser.PPI(1.0 wt%)was not sufficient to form a high internal phase emulsion,whereas PPI-SA with the same protein concentration could stabilize the high internal phase emulsion(the volume fraction of internal phase was 75%).On the one hand,HU-PPI had better emulsifying properties compared to unmodified commercial PPI(CPPI),and could stabilize HIPPEs in the presence of lower SA concentrations.On the other hand,compared with C-PPI-SA mixture,HU-PPI-SA complex stabilized HIPPEs had smaller particle size,more homogeneous and compact microstructure,higher energy storage modulus,and apparent viscosity,and could be used as ink for 3D printing of food.(3)Construction of High internal phase W/O/W double emulsion stabilized by modified PPI-SA complex and its application in co-delivery of hydrophilic and hydrophobic functional nutrients: The W/O/W double emulsions with high internal phase were prepared with different external aqueous phases(C-PPI,C-PPI-SA mixture,HU-PPI,and HU-PPI-SA complex),and their stability and rheological properties were compared.These systems were then used to encapsulate both the hydrophilic riboflavin sodium phosphate and the hydrophobic β-carotene.The digestion properties of double emulsion and the bioaccessibility of different polar functional nutrients were analyzed by simulating digestion models in vitro.The results showed that high-pressure homogenization and ultrasonic treatment of PPI and/or the addition of SA could enhance the ability of PPI to stabilize double emulsion.The double emulsions stabilized by HU-PPI-SA complex had smaller particle sizes,more uniform particle size distribution,stronger stability,and greater elastic modulus and apparent viscosity compared with other groups.The high internal phase double emulsion could realize the co-encapsulation of hydrophilic and hydrophobic functional factors,which significantly improved the photostability of the two functional nutrients.The double emulsion stabilized by HU-PPI-SA complex had the best protective effect on functional nutrients,which could maintain structural stability during simulated gastric digestion,and significantly improved the bioaccessibility ofβ-carotene.In conclusion,this study improved the properties of PPI as a carrier matrix through physical co-modification and its interaction with SA.High internal phase Pickering emulsion based on modified PPI-SA complex could be used for food 3D printing.And the W/O/W double emulsion with a high internal phase could be used for co-delivery of hydrophilic and hydrophobic functional nutrients.