Promoting Effects of Different Organic Acids on the Formation of Transglutaminase-Induced Cross-Linked Soybean Protein Isolate Hydrogels

Area of Science:

• Food Science and Technology
• Biochemistry
• Materials Science

Background:

• Microbial transglutaminase (mTG) improves soybean protein isolate (SPI) gelling but has limitations.
• Developing novel methods to enhance SPI hydrogel properties is crucial for food applications.

Purpose of the Study:

• To develop a dual modification technique using mTG and organic acids (GDL, LBA, MBA) for fabricating robust SPI hydrogels.
• To investigate the impact of organic acids on the structural and functional properties of mTG-modified SPI hydrogels.

Main Methods:

• Soybean protein isolate (SPI) was treated with mTG in combination with glucose-δ-lactone (GDL), lactobionic acid (LBA), or maltobionic acid (MBA).
• Gel strength, textural properties, water-holding capacity, surface hydrophobicity, intrinsic fluorescence, rheological properties (G', G″), particle size, and zeta potential were analyzed.
• Structural changes were assessed using circular dichroism (CD) spectroscopy to analyze secondary structures (β-sheet, α-helix) and subunit dissociation (11S to 7S).
• Intermolecular interactions were investigated, and water state and aggregate structure were confirmed using LF-NMR and SEM.

Main Results:

• mTG combined with GDL, LBA, or MBA significantly improved SPI hydrogel gel strength, texture, and water-holding capacity.
• Organic acid treatments reduced surface hydrophobicity and intrinsic fluorescence while increasing storage/loss moduli, particle size, and zeta potential.
• Structural analysis revealed increased β-sheet content, decreased α-helix content, and dissociation of SPI 11S subunits into 7S subunits.
• LF-NMR and SEM confirmed water immobilization and the formation of a dense, stacked aggregate structure, indicating enhanced gel network formation.

Conclusions:

• GDL, LBA, and MBA, when used with mTG, effectively enhance SPI hydrogel properties by promoting covalent and non-covalent interactions.
• The dual modification strategy leads to improved gel strength, stability, and water-binding capacity in SPI hydrogels.
• These organic acids are promising agents for combination with mTG in fabricating high-performance SPI hydrogels for various applications.