Study On The Construction And Stability Of W/o/w Emulsion Based On Alkali-heat Treated Rice Dreg Glutenin

In the rice sugar industry,a large amount of by-product rice dreg is produced,which has a high protein content.However,due to its poor solubility,it is difficult to apply in the food industry.Glutenin is the main component of rice gluten protein.In response to the solubility of gluten in alkaline solutions,alkali heat treatment was used to modify rice gluten protein.The effects of alkali heat treatment conditions on the structure and functional properties of rice dreg glutenin,and the effects of emulsification mode,water phase composition and oil phase volume fraction on the stability of alkali heat treated rice dreg glutenin(AHRDG)based w/o/w dual lotion were studied.Modified rice dreg gluten was prepared under different alkaline heat treatment conditions(pH 10,11,12,heat treatment temperature 45,55,65,75,and 85 ℃),and the effects of alkaline heat treatment on the structure,solubility,and emulsification of gluten were studied.By Fourier transform infrared spectroscopy,endogenous fluorescence spectroscopy,ultraviolet absorption spectroscopy and the changes in ζpotential,free sulfhydryl and disulfide bond content,and solubility showed that with the increase of heat treatment temperature at pH 10 and pH 11,the secondary structure of rice dreg glutenin transformed into disorder,and the spatial structure first unfolded and then curled.The protein ζ-The absolute value of the potential increased from 24.76 mV to 40.90 mV and then decreased to 28.57 mV;The free sulfhydryl content first decreases and then increases,and the disulfide bond content first increases and then decreases,resulting in an increase in solubility and then a decrease.It reached its maximum(38.99%)in the pH 11 and 65℃ heat treatment groups.At pH 12,as the heat treatment temperature increases,the secondary structure of rice dreg glutenin becomes orderly;Proteins undergo refolding or misfolding to form sheet-like structures,ζ-The potential decreased from-33.50 mV to-27.56 mV;The content of free thiol groups increases,while the content of disulfide bonds decreases,resulting in a decrease in solubility from 36.51%to 26.87%.The changes in the content of free sulfhydryl groups result in changes in the proportion of hydrophilic and hydrophobic groups and changes in the spatial structure,leading to changes in the emulsification characteristics of proteins.The results of emulsification and emulsification stability show that the emulsification performance(48.15,46.73 m2/g)of rice dreg gluten treated at 55 and 65℃ at pH 11 is improved compared to untreated rice dreg gluten(33.98 m2/g),but overall,alkaline heat treatment did not improve the emulsification performance of rice dreg gluten.AHRDG heat treated at pH 12 and 55℃ was selected as the research object to prepare double emulsions together with span80,to explore the effect of protein concentration on the centrifugation and storage stability of double emulsions under onestep emulsification,and the effect of water phase ratio and protein phase of two-step emulsification on the centrifugation and storage stability of double emulsions.Under the one-step emulsification method,when the protein concentration increases from 0.5%to 2.5%,the emulsions particles move in the radial direction of small particle size.When the protein concentration is 2.5%,the emulsions particle size is ≤17.18μm;The apparent viscosity,centrifugal stability,and storage stability increase,and the viscoelastic properties transition to viscosity.It is optimal at a protein concentration of 2.5%.The whey precipitation index after centrifugation is 10.56%,and there is almost no stratification after 96 hours of storage.When the concentration of emulsions protein was 3.0%,the distribution of large droplets,the decrease of apparent viscosity,centrifugation and storage stability appeared in the particle size distribution.After centrifugation,the precipitation index of whey was 16.48%.After 96 hours of storage,free water phase appeared,but the viscoelasticity increased.The results showed that the stability of the double emulsions could be enhanced by properly increasing the protein concentration.Under the two-step emulsification method,the volume of the internal water phase increases,the apparent viscosity of the emulsions first increases and then decreases,the viscoelastic property changes to elasticity,the particle size distribution first moves to the direction of small particle size and then moves to the direction of large particle size,the centrifugal and storage stability first increases and then decreases,both reaching the best in 15%of the internal water phase,and the whey precipitation index of the double emulsions with protein in the internal water phase and without protein in the internal water phase after centrifugation is 11.45%and 22.06%,respectively,And stratified at 1 hour and 48 hours,respectively.The stability of the double emulsions prepared by two-step emulsification method is worse than that by one-step emulsification method.Under proper internal water phase volume,the stable double emulsions can be prepared by adding protein to the internal water phase.Finally,the influence of oil volume fraction in the double emulsions with 2.5%and 3.0%protein content on the centrifugal stability,freeze-thaw stability and structure of the double emulsions was studied under one-step emulsification.The results show that with the increase of oil phase volume fraction,the apparent viscosity and viscoelasticity of emulsions at different temperatures are enhanced,the area of thixotropic ring is increased by about 2000 times,and it is transformed into a gelled high internal phase emulsions.The centrifugal and freeze-thaw stability of emulsions are improved.Compared with the 3.0%protein concentration double emulsions,the 2.5%protein content may not form a good high internal phase emulsions with the change of the oil phase volume,which indicates that the protein concentration not only affects the properties of the high internal phase emulsions by improving the interface strength,but also accelerates the change of the emulsions state by improving the system congestion.