Strategy And Mechanism Of "Two-Step Emulsification" To Improve Globulin Emulsification Efficiency And Emulsion Stability

Emulsion is inseparable from human life.Globulin has high nutritional value and has physiologically active functions,and has good amphiphilic baking,making it a good emulsifier.But its emulsification is susceptible to various factors,such as ionic strength(Na Cl).The study of the effect of ionic strength on protein-based emulsions has focused on stability.However,most of them simply attribute it to electrostatic shielding,and the systems explored are mostly low oil phase emulsions(LIPEs).Therefore,the understanding of relevant aspects has certain limitations.In recent years,high internal phase emulsions(HIPEs)shows great application potential in the fields of food and medicine.Globulin-stabilized HIPEs also are received more and more attention.Therefore,it is particularly important to systematically investigate the effect of ionic strength on the emulsifying properties of different types of globulin and its mechanism of action.This thesis selected three types of typical globulins,?-conglycinin(SC),glycinin(SG)and bovine serum albumin(BSA)and the responsiveness of their emulsification performance under various ionic strengths was investigated as follows:Firstly,the physico-chemical and structural properties of the effects of various ionic strengths(0-1000 m M,Na Cl)on laboratory-made SC and SG(protein content of 90.5% and 94.8%,respectively),as well as BSA were studied.It shows that the mechanism of the influence of ionic strength(I)on protein physico-chemical and structural properties is mainly electrostatic shielding(low concentration)and hydration repulsion(high concentration).The three types of globulin ware subject to the same level of electrostatic shielding.Solubility is negatively correlated with the average particle size of protein particles: the polymeric globulin(SC,SG)first aggregated strongly(I=50?100 m M),the solubility decreased,while the average particle size increased(from 55.7 nm to 117.8 nm,and from 105.0 nm to 26.5 ?m).Then the solution was clarified again due to the increase of hydration repulsion(I>300 m M),the solubility increased,while the average particle size decreased(maintaining ?80 nm,?30 nm,respectively).However,due to the small particle size of BSA,the electrostatic shielding is limited by the hydration repulsion,and the average particle size did not change significantly(8.8?11.0 nm),but promoted its solubility to some extent.In terms of protein structure,the high concentration of ionic strength(I>300 m M)makes the subunit conformation more rigid.Secondly,three types of globulin solutions(with various ionic strengths)were emulsified by ultrasound to prepare LIPEs(?=0.2)and by high-speed shear homogenization(one-step shear)to prepare HIPEs(?=0.8),respectively.It shows that,ionic strength helps to enhance the emulsifying activity of globulin,because the electrostatic shielding increases the diffusion rate of the protein and the amount of interfacial adsorption.For SC and SG,polymer balls with Pickering effect,ionic strength improved the emulsifying activity by enhancing Pickering stability of them.In terms of emulsion stability,ionic strength exacerbated the rate and extent of fat floating of SC-LIPEs and SG-LIPEs,but it can help to increase the storage modulus of SC-HIPEs and SG-HIPEs.The creaming stability of BSA-LIPEs is not sensitive to ionic strength,but because BSA easily expands at the interface to form a high-brittle film,which is different from the mechanism of SC and SG stable emulsions,BSA-HIPEs rapidly demulsify under the interference of ionic strength.Finally,for the sensitivity of storage stability of BSA-HIEPs to ionic strength,combined with the enlightenment of the Pickering Stabilization Mechanism of SC and SG,it can be significantly improved by the "Two-step" emulsification.It shows that the "Two-step" emulsification uses micro-droplets in the initial emulsion as stabilizers to prepare HIPEs.BSA significantly enhances its steric hindrance through the form of micro-droplets,and the storage stability of the prepared HIPEs was significantly improved.After 20-day storage at room temperature,there was no obvious change in appearance.Changing I,G' of HIPEs is similar to SC-HIPEs and SG-HIPEs,strengthening with the increase of I.Not only that,compared to onestep shear,the "Two-step" also reduced the minimum protein concentration required to stabilize HIPEs(from more than 0.2wt.% to less than 0.1wt.%),improving the emulsification efficiency of BSA.