Study On The Structure Changes And Recovery And Application Technology Of Peanut Protein In The Water Phase Of Aqueous Extraction Processing

Aqueous extraction processing(AEP)has the attributes of mild reaction condition,higher quality of oils,high resource utilization rate and environmentally friendly.After a half century of research,AEP has been initially realized industrialization.Still,plenty of other issues have to be resolved,such as absence of recovery and utilization technology for protein,water consumption and a large amount of wastewater.The objectives of this study were to(1)investigate the changing of peanut protein during AEP;(2)evaluate the differences of structural and functional properties between peanut protein powders(PPPs)prepared by conventional oil extraction processing and AEP combined with acid precipitation;(3)recover peanut protein from water phase by membrane technology and desalinated totally soluble peanut protein(SPP)and peanut protein aggregate(PPA)were obtained;(4)provides a new way for the recycle of permeate in AEP;(5)to improve functional properties of peanut protein aggregate by ultrasound treatment.The main contents and results are as follows.Firstly,the extraction yield of peanut oil and protein can reach the maximum value at the industrial AEP extraction condition(pH 9.0,60? and 2 h),approximately 95%and 75%respectively.The component composition and molecular weight distribution of peanut protein in the water phase changed during the industrial AEP.The relative content of conarachin ?decreased while that of conarachin ? increased.The content of protein aggregate increased from 5.1%to 7.5%.The content of free thiol decreased from 0.59 ?M to 0.43 ?M.Besides,the second structure of peanut protein in the water phase did not mainly change and the third structure changed to a tighter structure.Meanwhile,the surface hydrophobicity of peanut protein increased under the condition of the industrial AEP.The effect of the recovery method of protein in the water phase on the quality of protein powder was further studied.Spray-drying after acid precipitation and spray-drying after vacuum concentration were applied to recover protein in the water phase.The purity of protein powder obtained was 75.40%and 59.80%respectively and the solubility of the protein powder obtained was 63.75%and 27.67%.The protein powder obtained by spray-drying after vacuum concentration limited its application in the food industry and spray-drying after vacuum concentration could not be the optimum recovery process of peanut protein in water phase.Using spray-drying after acid precipitation as the recovery process,the structural and functional properties of peanut protein concentrates prepared by traditional oil extraction process and AEP were studied.The results showed that the purity and solubility of PPP of AEP(Peanut protein powder of AEP)were lower than PPPs prepared by traditional oil extraction processing.Relative content of conarachin ? in PPP of AEP was lower than PPPs prepared by traditional oil extraction processing and conarachin ? was opposite.Macromolecules aggregate formed during AEP and the PPP of AEP showed a looser structure.In addition,compared with PPP prepared by traditional oil extraction processing,PPP of AEP showed higher surface hydrophobicity and water holding capacity but lower emulsify capacity and emulsify stability.Compared with spray-dried PPPs,freeze-dried PPPs showed higher solubility,water and oil holding capacity,but lower emulsify capacity and stability.The functional properties of-PPP of AEP was influenced by its high ash content(?3.9%)and high residual oil(?2.8%).Appropriate salt concentration can improve the functional properties of PPI,but high residual oil will significantly reduce the functional properties of PPI.Therefore,without changing the prerequisite of AEP process,other methods should be found for recovery of peanut protein in the aqueous phase of AEP.The membranes separation technology was used to recover peanut protein from water phase.Microfiltration membrane(0.45 ?m,PVDF)was used for protein recovery from aqueous phase.The optimal rentention rate and the purity of peanut protein was of 55.76%and 82.12%respectively.The residual oil in PPA was 1.83%The influence of pore sizes of ultrafiltration membrane on the retention rate and desalting effect of peanut protein were investigated.Ultrafiltration membrane of 1 kDa was selected as the follow-up optimal choice.The effects of pH,transmembrane pressure and operating temperature on the retention rate and purity of ultrafiltration proteins were researched.The optimal operating conditions were original pH,1.5 Bar and 30?.The recirculation of MF permeate in AEP was studied.The results showed that the oil and protein yield of deionized-water-AEP was higher than that of the-third-cycle-ultrafiltration-permeate-AEP.The oil yield decreased from 96.51%to 95.30%(p>0.05),and the protein yield decreased from 75.70%to 71.35%(p<0.05).The product yields of the-third-cycle-ultrafiltration-permeate-AEP and eionized-water-AEP were very similar.Recycle of permeate in AEP can reduce the consumption of water effectively,dosage of alkali and wastewater generation.The cause and aggregation force of protein aggregation during MF were explored,and in vitro digestibility of PPA was analyzed.The result showed that circulating pumping was the main factor of protein aggregation during microfiltration.PPA and peanut protein isolate(PPI)presented similar isoelectric point values while the surface of PPA molecule contained more hydrophobic groups.The in vitro digestibility of PPA was lower than PPI during pepsin and trypsin digestion.The FTIR results show that more ?-sheet and ?-helix folds and less-helix in PPA,which mean higher degree of aggregation.In addition,according to SDS-PAGE analysis more with peanut globulin ? involved in the formation of protein aggregation.Binding forces analysis showed that hydrophobic interaction was the main force limiting dissolving of PPA,followed by disulfide bond.Finally,ultrasonic treatment was used to improve the solubility and emulsification of PPA,and the stability of the emulsion prepared by modified PPA was studied,and the particle size,protein composition,relative molecular distribution,secondary structure and the disulfide bond changes of modified PPA were further studied for revealing the mechanism of ultrasonic treatment to improve the functional properties of proteins.The results showed that the ultrasonic power presented a significant effect on the solubility of PPA.With improvement of ultrasonic power,solubility and emulsification of PPA increased.The emulsion prepared by modified PPA showed smaller particle size,higher zeta potential,higher storage stability and higher oil load(up to 60%).Analysis of solubility,molecular weight distribution,particle size distribution,endogenous fluorescence analysis and thermal stability confirmed that insoluble particles dispersed to dissolve and soluble protein aggregates were generated caused by cavitation when the ultrasonic power was low(200 W-500 W).However,protein aggregates dissociated when the ultrasonic power was increased to 800 W.