Soy protein interactions with polyphenols: Structural and functional changes in natural and cationized forms.

Area of Science:

• Food Science
• Protein Chemistry
• Biomaterials

Background:

• Soy protein isolate (SPI) is a common food ingredient with functional properties.
• Modifying SPI can enhance its performance as an emulsifier and antioxidant.
• Ethylenediamine (EDA) and gallic acid (GA) are known to interact with proteins.

Purpose of the Study:

• To synthesize cationic soy protein isolate (NSPI) by grafting EDA onto SPI.
• To form and characterize NSPI-gallic acid (GA) complexes.
• To evaluate the impact of NSPI-GA complexation on protein functionality, including emulsifying and antioxidant capacities.

Main Methods:

• Synthesis of NSPI via EDA grafting onto SPI.
• Formation of NSPI-GA complexes at various ratios.
• Characterization of structural, thermal, particle size, emulsifying, and antioxidant properties.
• Analysis of protein-ligand interactions using spectroscopic methods.

Main Results:

• EDA grafting imparted a positive charge to SPI, creating NSPI with uniform particle size.
• NSPI exhibited enhanced thermal stability, emulsifying ability, and antioxidant capacity compared to SPI.
• NSPI showed increased amino groups and stronger interactions with GA.
• EDA and GA synergistically increased protein flexibility, altering secondary structure (reduced α-helix, increased random coil).
• Interactions were identified as static, hydrophobic (GA-SPI), and electrostatic (GA-NSPI).

Conclusions:

• Grafting SPI with EDA significantly improves its functional properties.
• NSPI-GA complexes demonstrate enhanced emulsifying and antioxidant capabilities.
• The modified protein-ligand complexes hold potential as functional ingredients in food systems.