Isoelectric Point and Milk Coagulation pH

The isoelectric point ($\text{pI}$) is the specific $\text{pH}$ at which a protein carries no net electrical charge. For milk proteins, particularly caseins, minimal solubility and maximum aggregation (coagulation) occur at their isoelectric point.

Milk coagulation is influenced by $\text{pH}$ changes.

• At the isoelectric point, the repulsive forces between protein molecules are minimized, allowing them to clump together, leading to coagulation.
• The primary milk proteins, caseins, exhibit minimum solubility and thus maximum precipitation or coagulation around a $\text{pH}$ of 4.6.

Therefore, the isoelectric point of milk, which results in maximum coagulant activity (or minimum solubility leading to precipitation/coagulation), is 4.6.