Fabrication,Physicochemical Properties And Formation Mechanism Of Plant Protein Hydrogels Induced By Electric Field

Increasing the proportion of plant protein in the diet and reducing the intake of animal protein can not only reduce the environmental burden and greenhouse gas emissions,but also reduce the risk of mortality from cardiovascular disease,dementia and all-cause mortality.In recent years,replacing partial animal protein with plant protein has become a hot topic in future food production.Protein hydrogel is a common form of food in daily life,which is mainly prepared via acid induction,heat induction,salt induction and enzyme induction.To innovate the basic research and processing technology of protein hydrogels,electric field technology as a new processing technology has great potential in the preparation of edible protein hydrogel.Based on the low-voltage electric field technology,this study constructed two protein hydrogel systems:anisotropic protein hydrogels and phase separation hybrid hydrogels.The gel fraction,microstructure,water holding stability,textural properties,and swelling resistance of hydrogels were examined,and the potential mechanism of plant protein hydrogels was discussed through the analysis of protein structure and molecular interaction.The main research findings are as follows:Soy protein isolate(SPI)hydrogels with anisotropic structure were constructed through low voltage electric field(1.5 V/cm)and different Na Cl concentration(100～500 mmol/L).Under weak DC electric field,proteins with negative charge were ordered and accumulated in the direction of the electric field at the anode,while the surface charge of amino acids was shielded by local H~+and added Na~+.At the same time,the random coil in the secondary structure of proteins disappeared,forming more ordered structures,namelyα-helix andβ-turn content increased,and exposing more hydrophobic and thiol groups.Interactions between molecules,including disulfide bonds,hydrogen bonds,and hydrophobic interactions,promoted protein molecules to crosslink and form hydrogels.All protein hydrogels showed anisotropic structure,but the increase of ion concentration would destroy part of the ordered structure of hydrogels.When Na Cl concentration was 100 mmol/L,the pore size of hydrogels was relatively small(7.38μm)and the network structure was uniform,while when Na Cl concentration was more than 200 mmol/L,the pore size of the hydrogel became larger(12.60～15.34μm)and the network structure became uneven.As Na Cl concentration increased from 100 mmol/L to 500 mmol/L,the proportion of SPI attached to the gel phase(36.80%～62.17%)increased,and the hardness(96.13～210.54 g),springiness(33.88%～68.30%),chewiness(121.59～292.12 g·s)and swelling resistance(142.79%～54.20%)of protein hydrogels were gradually enhanced.However,with the increase of ionic strength,the water holding stability of hydrogels decreased from 99.62%to 66.75%,which may be due to the enlarged pores within network structures,making it easier for water to migrate.Hybrid hydrogels with phase-separated structures were fabricated using particulate soy protein and fibrous soy protein as raw materials.After applying a weak direct current electric field,fibrous proteins and particulate proteins moved and aggregated towards the anode.The electric field treatment caused changes in the secondary structure of proteins,leading to an increase in the content ofβ-turn structures,as well as an exposure of more hydrophobic and thiol groups.The interactions between molecules were mainly through electrostatic interactions,hydrophobic interactions,and disulfide bonds,which promoted cross-linking between protein fibers and particulate proteins to form hybrid hydrogels composed of protein hydrogels and protein fiber hydrogels.All hybrid hydrogels exhibited a phase separation structure,with the presence of fine chain regions and sparse granular regions.The addition of protein fibers formed at different hydrolysis times had no significant effect on the gel fraction of hybrid hydrogels,while incorporation of protein fibers obtained by acid heat in short time helped to improve the hardness(245.46～125.22 g),chewiness(527.05～250.16 g·s),and water holding stability(85.75%～72.92%)of hybrid hydrogels.In addition,all hybrid hydrogels showed excellent swelling resistance,possibly due to their dense network structure which prevented water infiltration and the strong network structure which prevented hydrogel deformation.In addition,compared with the constructed anisotropic protein hydrogels,the phase separation hybrid hydrogels had higher hardness(245.46 g),chewability(527.05 g·s)and swelling resistance without the addition of external ions.