Effects Of Enzymatic Cross-linking And Microfluidization Treatment On Conformational And Functional Properties Of Peanut Protein

This paper takes low-temperature defatted peanut meal as raw material. Peanut protein isolate (PPI) and its fractions (arachin and conarachin) were extracted from this meal and treated by the transglutaminase (TGase) cross-linking and/or microfluidization. The effects of these treatments on functional, physicochemical, and conformational properties of PPI and its fractions were studied.It was found that the increase of TGase incubation time (37°C, 0-240 min) resulted in the increased high molecular (> 66.2 kDa) subunits and polymers, decreased free amino groups, and promoted extent of cross-linking of PPI. The increased extent of cross-linking could enhance the thermal stability but decrease the solubility (pH 3.0-10.0) of PPI. After TGase cross-linking, the emulsifying activity of PPI was decreased. Limited TGase cross-linking (37°C, 90 min) could improve the emulsion stability of PPI but more increased extent of cross-linking could result in decrease of the emulsion stability. After PPI treated by TGase cross-linking, there was a decrease in the total free SH content and an increase in the exposed free SH content and surface hydrophobicity. It was also found that limited TGase cross-linking (37°C, 90 min) had beneficial effect on unfolding the PPI structure.For peanut protein fractions, there was a certain difference on the functional and conformational properties between arachin and conarachin. Compared with the arachin, the solubility and emulsifying properties of conarachin were better and the total/exposed free SH content and surface hydrophobicity of conarachin were higher, suggesting that the structure of conarachin was more unfolded. The cross-linking behaviors in arachin and conarachin under the catalyzing of TGase were also different. Compared with the arachin, the cross-linking reactions were more likely to occur in subunits of conarachin, and the higher molecular weight (> 97.4 kDa) subunits were formed in conarachin. The transition from small molecules to large molecules was more obviously observed in conarachin. The solubility and emulsifying activity of cross-linked peanut protein fractions were decreased, but limited TGase cross-linking could markedly improve the emulsion stability of conarachin.The effects of the modification of microfluidization followed by TGase cross-linking on functional and conformational properties of PPI and its fractions (arachin and conarachin) were studied. The results showed that microfluidization could improve the susceptibility of PPI and its fractions (arachin and conarachin) to TGase and induced more cross-linked subunits and G-L isopeptide bonds at the same conditions of TGase cross-linking. Compared with the peanut protein treated by microfluidization, the emulsion stability of the peanut protein treated with the microfluidization followed by TGase cross-linking was more improved. Compared with the peanut protein treated by TGase cross-linking, the solubility and emulsifying activity of peanut protein treated with microfluidization followed by TGase cross-linking were more promoted. Microfluidization and TGase cross-linking could both unfold the structure of peanut protein, and the microfluidization followed by TGase cross-linking could more easily unfold the structure and induced the decrease of total free SH content and the increase of exposed free SH content and surface hydrophobicity in peanut protein. Moreover, compared with the individual treatment, microfluidization followed by TGase cross-linking could more easily change the secondary structure of peanut protein, resulting in the decrease ofα-helix andβ-turns levels and the increase ofβ-sheet and random coil levels.The effects of microfluidization on cross-linked peanut protein were investigated. The results showed that microfluidization (40-160 MPa) could improve the solubility and emulsifying properties of cross-linked PPI, and the treatment of microfluidization at 160 MPa could lead a greater improvement. Microfluidization could also improve the solubility and emulsifying properties of cross-linked peanut protein fractions. Compared with the cross-linked conarachin, the cross-linked arachin treated by microfluidization had more improved solubility and emulsifying properties. After microfluidization treatment, the enhanced surface hydrophobicity, decreased particle size, and increased content of the soluble and small molecule were observed in the cross-linked peanut protein.