Study On Construction,Application,and Mechanism Of Wheat Gluten Based Emulsion Gels

Many common foods are protein-stabilized emulsion gels,such as mayonnaise and yogurt,etc.,which have gel-like structure of emulsions.In emulsion gels processing,for providing semi-solid food structure and creamy oral perception,it is generally required for formation of protein network in the continuous phase of the emulsion,or substantially increase the concentration of emulsifier to enhance the interfacial structure for stabilizing high content of oil droplets.Consumers are becoming increasingly concerned about clean label and natural foods.Using a novel processing strategy and exploring protein with excellent network formation and interfacial properties,which is helpful to construct ideal structure of emulsion gels.Wheat gluten(WG)is a common plant protein ingredient,which is mainly divided into monomeric gliadin and polymeric glutenin.Gliadin and glutenin as two major components of WG can crosslink to form a strong protein network,which contributes to stabilize the expanding gas in the dough during fermentation or baking,indicating that WG has strong network structure and interfacial activity.However,the excessive amount of non-polar amino acids in WG and poor water solubility limit its application in food emulsion gels.Therefore,in this thesis,WG and its components(gliadin and glutenin)were used as raw materials.We explored to improve solubility and make full use of the structural characteristics by controlling protein cross-linking and using novel dispersing solvent,and on the basis,diverse functional emulsion gels were constructed.Meanwhile,the mechanism of the effect of gliadin and glutenin on the structure and rheological behavior of emulsion gels was also evaluated.This thesis provided theoretical basis and novel strategy for the systematic research and application of emulsion gels in functional food.The main conclusions are as follows:(1)Gliadin as a component of WG was regarded as the research object,gliadin nanoparticles were prepared by anti-solvent method,and microfluidization initiated interfacial covalent cross-linking of gliadin particles at room temperature to construct algal oil emulsions gels.The results showed that microfluidization triggered interfacial cross-linking of gliadin through the intermolecular disulfide bonds at the interface,which induced the formation of the close packing of emulsion droplets to form structured emulsion gels.The viscoelastic and mechanical properties of emulsion gels were improved significantly with increasing pressure.Additionally,gliadin formed a cross-linking network at the interface,which acted as a physical barrier to effectively reduce lipid hydroperoxides and volatile hexanal of algae oil during storage of emulsion gels.(2)Hot edible glycerol was used as a novel solvent for WG to construct WG-based oil-inglycerol emulsion gels,and developed a simple and economical strategy for oil structuring,which could be used to construct solid fats without trans fatty acids.The results showed that emulsion gels(60 wt% oil content)with minimum WG concentration(0.5 wt%)could be prepared.Gliadin played a dominant role in the formation of interfacial structure by interfacial assembly behavior,while glutenin enhanced the strength of interfacial structure due to the interfacial aggregation.The synergistic interfacial effects of gliadin and glutenin contributed to the formation of 3D protein network,and the uniform oil droplets were trapped into the network.The emulsion gels prepared at 1 wt% WG exhibited higher elasticity,good thixotropic recovery and thermal stability,indicating emulsion gels have the essential rheological properties to replace solid fat.(3)Preparation of freeze-thaw stable WG-based emulsion gels by incorporated deep eutectic solvents(DES)was studied.Low melting point DES(-32.76 °C)with glycerol/choline chloride molar ratio of 2:1 were achieved.Controlling the crystallization performance of the aqueous phase in the low temperature environment by regulating the aqueous phase composition of the emulsion by DES,and then water-diluted DES as solvent to dissolve WG,which was used to prepare emulsion gels.The results showed that with the increase of DES concentrations,the interfacial adsorption capacity and interfacial protein coverage of WG increased gradually,positively reflected in forming elastic gel-like emulsion with smaller droplet size.Higher concentrations of DES as cryoprotectants agents in the bulk phase and strong interfacial network of WG could prevent formation of the ice crystals and damage to the interface during the freezing process,resulting in formation of freeze-thaw stable emulsions after three cycles of treatment(-40 °C,24 h;25 °C,2 h).(4)This study developed plant protein-based emulsion gels as commercial mayonnaise replacers by constructing WG-stabilized oil-in-water high internal phase emulsions(HIPE).WG was dissolved into pH 3 45%(v/v)aqueous ethanol to form phase-separated WG particles,and then the ethanol was removed by using emulsification-evaporation method to prepare oil-in-water HIPE(75 wt% oil content).The results showed that the closely packed oil droplets were trapped into the interfacial protein network of HIPE and mayonnaise.It is worth noting that compared with mayonnaise,HIPE(1 wt% WG)had similar near-perfect thixotropic property(nearly 100%)and oral tribological sensory.Additionally,thermal stability of HIPE was much better than that of the mayonnaise.(5)The effect of controlling WG component on the microstructure and rheological behavior of emulsion gels with high oil content(60 wt%,75 wt%)was studied.Exploring the mechanism of gliadin and glutenin on formation of emulsion gel through small oscillation shear(SAOS)and large amplitude oscillatory shear(LAOS)test,and establishing the relationship between microstructure and rheological behavior of emulsion gels.The results showed that interfacial gliadin could stabilize the emulsion gels,and glutenin as a non-surface-active component could be enriched in the bulk phase to form the network.SAOS test showed that the values of storage modulus and crossover strain of emulsion gels increased with the increase of relative glutenin concentration in the viscoelastic region.However,in the LAOS test,addition of glutenin had opposite nonlinear responses to emulsion gels with different oil contents.When the oil content was 60 wt%,glutenin in the continuous phase was prone to fracture in the highfrequency shear environment,and the relatively small amount of gliadin adsorbed at the interface was not resistant to damage by large deformation to the emulsion structure.When the oil content was 75 wt%,the continuous phase was occupied by more oil droplets,thus glutenin had limited space for shear and torsion,which made glutenin hard to damage.Glutenin and gliadin adsorbed synergistically to form composite interfacial protein membrane surrounding the emulsion droplet.Both of them resisted the structural deformation synergistically at the interface under large strain.