Milk: Know the Particles, Know the Quality

Milk is an emulsion of butterfat droplets and casein micelles. The size of these particles can vary, which strongly affects the milk’s mouthfeel as well as its colloidal stability. Here we show that the Litesizer™ can monitor the particle size and the zeta potential of whole as well as skimmed milk, giving precious information about the quality and the stability of the product.

Milk is an emulsion of butterfat droplets within an aqueous solution of carbohydrates, minerals and several proteins, the most abundant being casein. Casein forms micelles in solution, which vary in diameter from about 100 to 200 nm. 

The flavor, mouthfeel and emulsion stability (tendency of the particles to separate out) of milk are strongly affected by the size of the fat globules and the casein micelles. If the particle size is too large, the particles might have a tendency to float up, which can lead to a phase separation (a process appropriately termed ‘creaming’). If the particle size is too small, the particles might flocculate. 

Another factor crucial to emulsion stability is the electrostatic charge carried by the particles. Particles that are highly positively or negatively charged will repel each other in solution and flocculation is less likely. The surface charge of the particle is typically characterized by the emulsion’s zeta potential, a measure of the sign and magnitude of the surface charge. 

Therefore, monitoring particle size and zeta potential is important for ensuring that milk meets the customers’ needs, the regulatory standards as well as the shelf-life requirements. 

Get the document

To receive this document please enter your email below.