Research On Recovery And Functionalities Of Peanut Protein Obtained During Aqueous Extraction Of Peanut Oil

Peanuts are rich in fat and protein.In addition to providing edible oils,it is a good resource of vegetable protein.In the process of extracting peanut oil by using Tween-assisted aqueous method,peanut protein in aqueous extract can be recovered at the same time,which is of great significance to enhance the added value of peanut products and effectively alleviate the shortage of protein resources in China.To date,the problems associated with peanut protein obtained during aqueous extraction of peanut oil were its high oil content,low purity,and poor functional properties.In this paper,the acid precipitation method and ultrafiltration membrane method were used to recover the protein in the water extract.The functional properties of peanut protein were determined and the effect of Tween-20 content on the emulsifying properties of peanut protein was mainly studied.Further use of transglutaminase to improve the gel properties and structural properties of peanut protein was investigated.The relationships between structure and function of peanut protein were analyzed.The results of the study are as follows:The optimal preparation process for determination of peanut protein water extract was as follows: solid-liquid ratio 1:6(w/v),pH values 10,extraction time 30 min,and Tween-20 addition 1.0%.Under these conditions,the protein extraction rate was 78.57%.The protein water extract of acid precipitation pH 4.5 and washing the protein precipitation twice were confirmed.Three methods of pretreatment were compared: alkali salt saponification,organic solvent extraction and high-speed centrifugation.The alkali salt saponification method was then used to treat the aqueous extract and acid precipitation process,the purity of obtained peanut protein powder was 81.28%,the residual oil content was 5.18%,the content of Tween-20 was 11.11%,and the protein recovery rate was 84.68%.The purity of peanut protein powder obtained by ultrafiltration membrane(5 kDa)was 77.35%,the amount of residual oil was 6.14%,the content of Tween-20 was 6.36%,and the protein recovery rate was 97.45%.The solubility,water-holding,oil-absorbing,foaming and foam stability of tree proteins were compared: Tween-20 extracted peanut protein(TPP),peanut protein isolates(PPI)and soy protein isolate(SPI).The results showed that the solubility of TPP was higher than that of PPI and SPI;TPP and PPI were similar in water holding capacity,but lower than SPI;TPP and PPI had similar foam stability,but higher than SPI;TPP had higher emulsification than PPI,but were both lower than SPI;short-term emulsifying stability of TPP was higher than that of SPI and PPI;in terms of oil-absorption and foaming properties,TPP,PPI and SPI had no obvious difference.The effect of Tween-20 content on the emulsifying properties of peanut protein was studied.The results showed that an appropriate amount of Tween-20 in the protein powder could significantly improve the emulsifying activity and short-term emulsifying stability of the protein,while excessive amount of Tween-20 weakened the emulsification properties.However,the emulsion containing Tween-20 protein powder had a significantly larger particle size after 2 days of storage,and more free oil was deposited on the surface after 5 days,indicating that it was more likely to destabilize as storage time prolonged.The Qingrui TGase enzyme was identified as an enzyme for TPP modification by enzyme screening.The conditions of cross-linking of TGase enzyme were optimized for TPP mixture(containing 15% tapioca starch)under neutral conditions: TPP concentration 15%,TGase enzyme addition amount 10 U/g,reaction time was 150 min.Under these conditions,the gel strength of the TPP mixture was 79.27 g.Under alkaline conditions,TPP could form a strong gel,but compared with PPI,the gelation of TPP is weak,and the presence of Tween might reduce the gel strength of TPP.When the pH was 8.5,the TGase enzyme was used to modify the TPP to obtain peanut protein powder with excellent gel properties(gel strength 395.06 g).It was found that obvious bands appeared on the top of TG-TPP,and partial acidic subunits of peanut globulin of TG-TPP were deficiency at the same time from the SDS-PAGE analysis.It indicated that TGase enzyme had significant cross-linking effects.By DSC analysis,compared with TPP and PPI,the denaturation temperature of TG-TPP increased significantly,and the enthalpy of heat decreased significantly.By Fourier transform infrared spectroscopy analysis,it was found that the contents of ?-sheet and random curl structure in TG-TPP were reduced,there was no significant change in ?-helix,and the content of ?-turn structure was increased,indicating that the secondary structure of proteins changed to some extent after crosslinking.According to surface hydrophobicity and endogenous fluorescence spectrum analysis,the surface hydrophobicity of TG-TPP increased,and the red fluorescence of the endogenous fluorescence spectrum appeared.Compared with TPP,TG-TPP not only significantly improved the gelling property,but also significantly increased oil-absorption,while solubility,emulsion stability,and foam stability all decreased significantly,and water holding capacity,emulsifying property,and foaming property were not significantly different.