Research On The Fabrication Of Gliadin-quercetin Complex And Their Characteristics Of Pickering Emulsion Based On PH/Sodium Chloride Regulation

In recent years,the influence of functional ingredients(such as polyphenols,polysaccharides,phospholipids)on the physical and chemical properties of food ingredients has received increasing attention,with an increasing of demand for new composite food systems in the food industry.The complex interactions of food components form composite particle structures,which manipulate the formation of food structures(such as emulsions,foam systems).pH and ionic strength are two important factors influencing the protein physicochemical properties and the interactions between proteins and other food components.Therefore,our study investigated the interaction mechanism and structural characteristics of wheat gliadin(G)and quercetin(Q),the surface hydrophobicity,thermal stability and foaming properities of G and G/Q.In addition,the study evaluated the rheological behavior and microstructure of emulsions prepared by G and G/Q composite particle.The study might give theoretical references for developing the high protein products that contained bioactivators.The results are listed as follows:(1)Based on the previous experiment,G/Q complexes at pH 2.0?9.0 were prepared at G to Q molar concentration ratio of 10:1.The interaction mechanism of G with Q was determined by multiple spectroscopic methods(fluorescence spectroscopy(FL),UV-visible absorption spectroscopy(UV-vis),fourier transform infrared spectroscopy(FTIR),Raman spectroscopy,ect).Results showed Q quenched the fluorescence intensity of G by dynamic and static quenching modes.Thermodynamic parameters suggested that hydrophobic force took charge of the formation of complexes at pH 2.0-4.0,whereas hydrogen bonds and van der Waals forces at pH 5.0-9.0.The secondary and tertiary structural alterations and microenvironmental changed aroundprotein fluorophores upon complexation with Q.The gauche-gauche-trans conformation increased at the expenses of the gauche-gauche-gauche conformation and the transition from ?-turn and random coil to ?-helix and ?-sheet at pH 5.0 might decrease the allergenicity of G.(2)The microstructure,surface hydrophobicity,thermal stability were determined at different pH conditions.SEM analysis showed that more porous and compact microstructures were formed with pH varied.DSC analysis demonstrated that protein denaturation peak was narrower at pH 5.0.(3)A simple homogeneous emulsification method was used to prepare the emulsion.The particle concentration was 5.0 mg/mL,the oil phase was soybean oil,and the oil/water ratio was 5.0 mg/mL.The emulsion formation and performance were studied at pH 3.0 and pH 5.0.Q-loaded emulsion possessed the highest viscosity and strongest gel performance at pH 5.0.The emulsions were stable(no oil deposition phenomenon)after 90 days storage.At pH 3.0,the continuous network structure of protein particles in the continuous phase had an important effect on the stability of emulsion,while at pH 5.0,the interaction between particles adsorbed at the interface of oil droplets and the interaction between oil droplets stabilized the emulsion.(4)G/Q complexes at different NaCl concentrations(0 mM,10 mM,20 mM,50 mM,100 mM,200 mM)were prepared at G to Q molar concentration ratio of 10:1.The binding characteristics of G with Q were determined by FL,UV-vis,FTIR,ect.Q quenched the fluorescence intensity of G by dynamic and static quenching modes(except at 20 mM NaCl concentration),the interactions between G and Q were hydrogen bonding,electrostatic interaction and hydrophobic interaction.Q changed the microenvironments of tryptophan and tyrosine residues,resulted in the rearrangement of protein secondary structure.The trans-gauche-trans conformation increased at the expenses of the gauche-gauche-gauche conformation.The gauche-gauche-gauche conformation disappeared with the addition of Q.(5)The microstructure,surface hydrophobicity,thermal stability were determined at different NaCl concentrations.SEM analysis showed that the fiber sheet protein structure turned into a more compact with some homogeneous small pores distribution microstructure due to the introduction of ions,while the aggregations of ions might be detrimental to their re-dispersion ability.DSC analysis demonstrated that protein thermal stability decreased with the introduction of ions,whereas the thermal stabilityof G/Q complexes was higher than that of G.(6)A simple homogeneous emulsification method was used to prepare the emulsion.The particle concentration was 5.0 mg/m L,the oil phase was soybean oil,and the oil/water ratio was 50%(v/v).The emulsion formation and performance were studied at 0 mM and 50 mM NaCl concentrations.Q-loaded emulsion possessed the highest viscosity and strongest gel performance at 50 m M NaCl concentration.Confocal laser scanning microscope showed that the emulsion with 50 m M NaCl concentration had more particles to stabilize the oil-water interface,and the emulsion formed a close packing structure.