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. 2025 Jun 18;14(12):2130.
doi: 10.3390/foods14122130.

Effect of TGase Crosslinking on the Structure, Emulsification, and Gelling Properties of Soy Isolate Proteins

Ziqi Peng  1 , Kunlun Liu  1 , Ning Liao  1
Affiliations

Effect of TGase Crosslinking on the Structure, Emulsification, and Gelling Properties of Soy Isolate Proteins

Ziqi Peng et al. Foods. .

Abstract

Soy isolate protein (SPI), as a high-quality plant protein source, is often processed into various soy products. In this study, the physicochemical properties of SPI treated with transglutaminase (TGase) were investigated in correlation with emulsification characteristics and rheological behavior. The polyacrylamide gel electrophoresis with sodium dodecyl sulfate (SDS-PAGE) and Fourier-transform infrared spectroscopy (FTIR) and endogenous fluorescence spectrum analysis results showed that TGase was able to promote the covalent binding of lysine and glutamine residues in SPI. The moderate pre-crosslinking treatment of TGase (5-7.5 U/g TGase pre-crosslinked for 2 h or 5 U/g TGase pre-crosslinked for 2-3 h) improved the emulsification and gel properties to varying degrees: the nanoparticle and emulsification performance increased by 24.35% and the storage modulus of the gel increased by 288%. Furthermore, the surface charge of SPI increased due to the crosslinking impact of TGase, indicating a considerable rise in the surface electrostatic potential. Simultaneously, the protein surface exhibited a substantial increase in hydrophobicity, while the level of free sulfhydryl groups reduced. These changes indicate that TGase enzymatic crosslinking could significantly improve the structural stability of nanoparticles by enhancing the generation efficiency of covalent bonds between protein molecules.

Keywords: conformational changes; crosslinking; properties; protein nanoparticles; transglutaminase.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1
Figure 1
SDS-PAGE profile of SPI crosslinking products (SPI, SPI with heat treatment (a), SPI crosslinked with different TGase enzyme concentrations, SPI of TGase crosslinking at different crosslinking times (b). Marker: The left side displays the matching molecular weight.
Figure 2
Figure 2
Effect of different TGase concentrations and crosslinking times on the size/PDI (a,b) and zeta potential (c,d) of SPI. Significant differences (p < 0.05) are indicated by different letters (a–c).
Figure 3
Figure 3
Effect of different TGase concentrations (a) and crosslinking times (b) on the H0 of SPI. Significant differences (p < 0.05) are indicated by different letters (a–d).
Figure 4
Figure 4
Endogenous fluorescence spectroscopy of SPI treated with different TGase concentrations (a) and crosslinking times (b).
Figure 4
Figure 4
Endogenous fluorescence spectroscopy of SPI treated with different TGase concentrations (a) and crosslinking times (b).
Figure 5
Figure 5
Infrared spectral analysis of SPI treated with different TGase concentrations (a) and crosslinking times (b).
Figure 6
Figure 6
Effect of different TGase concentrations (a) and crosslinking times (b) on free sulfhydryl groups (S0) of SPI. Significant differences (p < 0.05) are indicated by different letters (a–e).
Figure 7
Figure 7
Effect of different TGase concentrations (a) and crosslinking times (b) on the EAI and ESI of SPI. Significant differences (p < 0.05) are indicated by different letters (a–d).
Figure 8
Figure 8
Effect of different TGase concentrations (a) and crosslinking times (b) on the storage modulus (G’) of SPI gels.
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