Casein micelles: from the monomers to the supramolecular structure

Abstract

The most relevant aspect concerning casein micelles lies in the fact that all the procedures employed in the transformation of milk into dairy products depend, directly or indirectly, on their stability or their controlled destabilization. Thus, the present paper aimed to present an updated review of the structural organization of casein micelles. Physicochemically, casein micelles can be defined as spherical, porous supramolecular aggregates, highly hydrated, negatively charged, with a mean diameter of about 200 nm, and presenting approximately 10⁴polypeptide chains. Besides water, casein micelles are constituted of four types of casein molecule, namely α_S1, α_S2, β and κ-caseins, which are held together by means of hydrophobic and electrostatic interactions, and by the presence of minerals, mainly composed of calcium phosphate salts, which are considered the main factor responsible for maintaining the micellar structure. The stability of the casein micelles is attributed to the presence of an outer diffuse layer, basically composed of κ-casein. Although the colloidal properties of casein micelles are well known, there is still no consensus concerning their internal structure. Therefore, the main models describing the internal organization of casein micelles are presented in the final part of this article.

Keywords:
Casein micelle; Casein; Colloidal calcium phosphate; Milk proteins; α_S1-casein; α_S2-casein; β-casein; κ-casein