Structure and functionality of Pleurotus geesteranus protein isolate as a function of pH

Area of Science:

• Food Science
• Protein Chemistry
• Biochemistry

Background:

• Edible mushroom proteins have food application potential.
• Alkaline extraction-acid precipitation often yields poorly soluble proteins.
• Structural changes during acid precipitation are not well understood.

Purpose of the Study:

• Investigate pH effects on Pleurotus geesteranus protein isolate (PGPI) structure and function.
• Understand the reasons for poor solubility in acid-precipitated mushroom proteins.
• Develop a highly water-soluble PGPI.

Main Methods:

• Alkaline extraction, dialysis, and freeze-drying to prepare PGPI.
• Analysis of PGPI amino acid composition and molecular weight distribution (SDS-PAGE).
• Measurement of zeta potential, particle size, fluorescence intensity, and secondary structure (α-helix, β-sheet) across a pH range.

Main Results:

• PGPI is rich in essential and aromatic amino acids, with most proteins < 45 kDa.
• Isoelectric point (pI) of PGPI is 4.3; particle size increases away from neutral pH.
• Decreasing pH reduces α-helix, increases β-sheet content, and alters fluorescence, indicating more ordered structures.
• SS bond content and H0 peaked near pH 4, correlating with structural changes.

Conclusions:

• Lowering pH induces ordered protein structures in PGPI, explaining poor solubility.
• Structural changes significantly affect PGPI's functional properties (water/oil holding, foaming, emulsification).
• Dialysis and freeze-drying can yield a more soluble PGPI, but pH-dependent structural changes remain critical.