Heteroprotein complex between soy protein isolate and lysozyme: Protein conformation, lysozyme activity, and...

Area of Science:

• Food Science
• Biochemistry
• Protein Chemistry

Background:

• Heteroprotein complexes form through electrostatic interactions between oppositely charged proteins in aqueous solutions.
• Understanding the structure-function relationship of these complexes is crucial for developing tailored applications in food and biotechnology.

Purpose of the Study:

• To investigate the structural and functional properties of soy protein isolate/lysozyme (SPI/LYS) complexes.
• To analyze protein conformation, assembly structure, and enzyme activity at different mass ratios (2:1 and 1:1.3).

Main Methods:

• Formation and characterization of SPI/LYS complexes at specific mass ratios.
• Analysis of surface hydrophobicity under varying NaCl concentrations.
• Assessment of lysozyme (LYS) enzyme activity.
• Microscopy techniques to observe complex structure and particle size.

Main Results:

• Electrostatic complexation of SPI/LYS increased surface hydrophobicity, which decreased with increasing NaCl concentration, reaching a plateau at 200 mM NaCl.
• SPI/LYS complexes exhibited amorphous, flocculated structures with uneven protein distribution.
• Lysozyme activity remained largely unaffected by complexation.
• High dilution disassembled large complexes (>5 μm) into smaller particles (~100 nm), with NaCl further reducing particle size.
• Immobilized water was detected within the flocculated complexes.

Conclusions:

• SPI/LYS electrostatic complexation enhances surface hydrophobicity while preserving lysozyme activity.
• The complexes form amorphous structures that can be modulated by salt concentration and dilution.
• These findings provide insights into the physical chemistry of protein-protein interactions for potential food ingredient applications.