Journal of Dairy Research

Original Articles

Mineral and protein equilibria between the colloidal and soluble phases of milk at low temperature

Alice Pierrea1 and Gerard Brulea1

a1 Laboratoire de Recherches de Technologie Laitieère, Institut National de la Recherche Agronomique, CNRZ, 65 rue de Saint-Brieuc, 35042 Rennes Cedex, France

Summary

Mechanisms controlling exchange and partition of minerals and β-casein between micellar and soluble phases during cooling have been studied using suspensions of milk proteins of varying concentrations in the presence of aqueous phases having varying mineral compositions. In these studies the final equilibrium between Ca and phosphate was found to be regulated by formation of Ca phosphates of varying solubilities. The effect of the total casein level on mineral and protein equilibria was also studied. In milk, part of the β-casein content is bound to micelles by hydrophobic bonds; the proportion present in this form was increased by spontaneous micellar demineralization during cooling as well as by addition of a complexant to milk. At low temperatures, an equilibrium between the micellar and the monomeric states was reached which depends upon the total casein level and on the hydrophobic-bonded β-casein content. Not all of these hydrophobic bonds were broken when milk was cooled.

(Received December 02 1980)

(Accepted February 05 1981)