Casein Interactions: Casting Light on the Black Boxes, the Structure in Dairy Products

This paper reviews the literature on the interactions of the caseins and suggests that the state of association of these proteins is governed by a balance of attractive hydrophobic interactions and electrostatic repulsion. The effects of temperature, pH and ionic strength on the self-association and calcium-induced aggregation of the individual caseins are rationalized in terms of their influence on this balance of forces. The discussion is then extended to the nature of the interactions prevailing in the casein micelle and a dual-bonding model of the casein micelle is formulated, reflecting the need for two different forms of bonding in the network. This model plausibly accounts for the effects of temperature, pH, ionic strength, micellar dissociating agents and solvent on the integrity of the micelle in terms of their influence on the hydrophobic/electrostatic balance of forces. Finally, it is postulated that the same type of bonding prevails in casein gels produced by renneting or acidification. The model is then used to explain the influence of temperature on rennet gel strength, the effects of forewarming on rennet and acid coagulation properties of milk, and the effect of temperature on the viscoelastic properties of a concentrated micellar suspension.