Isoelectric point

The isoelectric point (pI) is the pH at which a molecule, usually a protein or peptide, has a net electrical charge of zero . At this pH value, electrostatic forces are balanced, resulting in low solubility and zero electrophoretic mobility .
This data is crucial in biochemistry, formulation, biotechnology, and nutrition , as it determines the behavior of biomolecules in solution and their physicochemical stability .

Knowing the isoelectric point of a protein makes it possible to optimize the conditions of formulation, separation or purification, but also to understand its interactions with other components (salts, lipids, polymers, excipients, etc.).

Principle and method of analysis

The determination of the isoelectric point is carried out by two main approaches:

• Acid-base titrimetry : progressive measurement of the pH of a solution containing the molecule of interest during a titration. The isoelectric point is deduced from the neutralization curve where the net charge is zero.
• Electrophoresis (IEF – IsoElectric Focusing) : separation of molecules according to their electrical charge in a pH gradient. Each protein migrates until it reaches its pH, where it becomes electrically neutral.

These techniques are suitable for the analysis of:

• protein extracts ( plants, yeasts, microorganisms, animal tissues),
• of cosmetic or nutraceutical formulations ,
• of colloidal solutions or stable suspensions,
• recombinant proteins or biotechnological products.

For additional analyses, discover:

• SDS-PAGE gel electrophoresis to separate proteins according to their mass,
• protein profile analysis to identify major fractions,
• and the dosage of amino acids to characterize the molecular composition.

Industrial and scientific applications

The measurement of the isoelectric point is used in many fields:

• Food industry and nutrition : formulation of functional proteins, stabilization of emulsions, study of solubility and interactions in enriched foods.
• Nutraceuticals and animal health : characterization of bioactive peptides, plant proteins or enzymes used as supplements.
• Cosmetics : formulation of products based on proteins, collagen or active peptides, the charge of which influences the stability of emulsions.
• Functionalized materials and polymers : study of surfaces modified by biomolecules or surfactants.
• Biotechnological research : purification and isolation of proteins by electrophoresis or ion exchange chromatography.

Knowledge of the isoelectric point makes it possible to predict stability, solubility and electrostatic interactions between molecules, thus improving the quality of formulations and industrial processes.

Analytical interest and complementarity

Isoelectric point analysis is part of a comprehensive approach to the physicochemical and biochemical characterization of molecules. It is often combined with other tests to obtain a complete view of protein behavior:

• pH measurement to assess formulation conditions,
• Zeta potential to analyze colloidal stability,
• UV-Vis spectroscopy to quantify protein concentration,
• Total protein assay to relate pI and protein content,
• Thermal stability tests (DSC) to monitor denaturation.

These combined analyses allow a complete characterization of the structure, charge and behavior of biomolecules , useful for research and industrial development.

YesWeLab Services

YesWeLab collaborates with a network of ISO 17025 and/or COFRAC , experts in biochemistry, physical chemistry and protein analysis .
Our specialists select the method best suited to your matrices and objectives: formulation, characterization, stability study or quality control.

Thanks to the YesWeLab digital platform , you can manage your analyses online, track your samples and consult your reports with complete transparency.
Since 2020, YesWeLab has been supporting the food, cosmetics, nutraceutical and biotechnology industries in controlling the quality and stability of their protein products.

For any specific requests or quotes, contact our scientific team today.