Study Of The Stability Of Pickering Emulsions With Salt Induced Rice Bran Protein And Its Application As Fat Substitute

Rice bran protein（RBP）has superior nutritional value,high water-soluble small molecule protein content and good emulsification properties,and presented potential on the Pickering emulsion stabilizer.Baking oils such as margarine and butter contain partially hydrogenated oils（PHOs）,which are the main source of trans fatty acids and are harmful to consumer health.Therefore,it is necessary to find other promising fat substitutes.In this study,rice bran protein nanoparticles were heated to prepare Pickering emulsions under different preparation conditions.The salt addition improved the stability of Pickering emulsions by affecting the protein structure and the mechanism of salt ions influencing Pickering emulsions was explored.Then Pickering emulsions were used as fat substitutes in bread to replace margarine and butter,thus developing healthy and nutritious baked food and promoting the application of rice bran protein in food.Firstly,the effect of protein concentration（3%,4%,5%）and oil phase proportions（φ=0.40,0.60,0.70,0.80）were studied on the properties of Pickering emulsions stabilized with rice bran protein.Rice bran protein particles were amphiphilic and could be used to prepare Pickering emulsions.With the increase of rice bran protein concentration,the interface layer grew thicker,the free protein particles in the aqueous phase filled the gaps between the droplets,the particle size of emulsions decreased,and the storage stability was improved.The increase of oil phase proportion caused the larger droplet size in the emulsions and the larger interface area.Moreover,Multiple droplets shared the interface facial mask,forming a gel network structure.80%oil phase emulsions（HIPEs）had good self-supporting properties.By comparison,the emulsions prepared at c=5%,φ=0.60 has good stability.Secondly,the Pickering emulsion prepared with the above preparation condition was used to explore the properties and structures of rice bran protein nanoparticles（RBPNPs）and the properties of the emulsions under different heating temperatures（45℃,60℃,75℃,90℃）.With heat conditions,the internal structure of RBPNPs unfolded and rearranged,exposing internal hydrophobic groups to form protein aggregations（191.40 nm to 265.97 nm）.Meanwhile,the random coils structures were induced at the expense ofα-helix structures,resulting in reduced flexibility structure and decreased interfacial protein adsorption rate（55.53%～50.52%）.However,it is difficult to desorb after the adsorption of protein at the oil-water interface,leading to the improvement of emulsion stability.Heated with a high temperature（90℃）,the protein structure irreversibly unfolded,forming a network structure with particles cross-linking,and the interfacial layer was shared between neighboring droplets.With the increase of temperature,the influence of protein structure was more significant,and the emulsifying stability and the thermal stability of emulsions increased,and the storage stability and oxidation stability decreased.Further study on the effect of salt ions on the structure of RBPNPs,properties of Pickering emulsions with different oil phase proportions（φ=0.60,0.80）and stabilized mechanism.With the increase of salt concentration,the particle size of emulsions decreased（15.25μm～12.02μm）,H₀ increased（536.5～1890.1）,and the adsorption rate of interfacial protein increased（58.65%～82.62%）,which enhanced the physical stability of emulsions.The addition of salt ions increased the electrostatic and hydrophobic interactions between particles,promoting the refolding and aggregation of proteins（Theα-helix structures were transformed intoβ-sheet and the random coils structures）,improving the adsorption of protein particles on the oil-water interface.Compared to Na Cl conditions,emulsions with Ca Cl₂（especially 200 m M）had more significant storage stability,with the droplet size almost unchanged（12.02μm～16.04μm）after7 days storage.It was mainly due to the enhanced complexation between the particles and Ca Cl₂,which increased the particle size（260.93 nm）,surface hydrophobicity（1890.10）and fluorescence intensity,thus forming a dense and unbroken interface layer.The emulsions contained highly viscoelastic gel-like structure.Salt ions improved the interfacial activity and oxidation resistance of RBPNPs,which were efficiently adsorbed to the oil-water interface to form a solid interface layer.Therefore,the network structure of emulsions was built through hydrophobic bond and ionic force,and stable Pickering emulsions were prepared.Finally,RBP stabilized HIPEs were utilized as fat substitutes to prepare breads and compared with commercially available butter.The effect of salt ion conditions on the properties of the bread prepared with HIPEs was studied.The appearance and color of the bread prepared with HIPEs are similar to those of the control sample.After replacing margarine with HIPEs,the contracted and fractured gluten network structure of dough became continuous and dense.As a result,the texture and properties of bread were improved,and the hardness and gumminess were reduced by 40%.The salt ions treated HIPEs bread had structural advantages,as the viscoelastic parameters（G’and G’’）of the dough increased and the specific volume（4.36～4.99）and elasticity（0.92～1.09）of the bread increased,resulting in more fluffy and elastic breads.In addition,the HIPEs bread was abundant in unsaturated fatty acids（79.5%）compared to the margarine bread（43.9%）,with trans fatty acids decreased to 0.The results showed that salt treated HIPEs bread had better edible properties than margarine bread,indicating that RBP stabilized HIPEs had higher feasibility in the application of baked goods.