Physical and chemical properties of cheese, such as texture, color, melt, and stretch, are primarily determined by the interaction of casein (CN) molecules. This review will discuss CN chemistry, how it is influenced by the cheese-making process, and how it impinges on the final product, cheese. We attempt to demonstrate that the application of principles governing the molecular interactions of CN can be useful in understanding the many physical and chemical properties of cheese and, in turn, how this can be used by the cheesemaker to produce the desired cheese. The physical properties of cheese (as well as flavor) are influenced by a number of factors including: milk composition; milk quality; temperature; the rate and extent of acidification by the starter bacteria; the pH history of cheese; the concentration of Ca salts (proportions of soluble and insoluble forms); extent and type of proteolysis, and other ripening reactions. Our hypothesis is that these factors also control and modify the nature and strength of CN interactions. The approach behind the recently proposed dual-binding model for the structure and stability of CN micelles is used as a framework to understand the physical and chemical properties of cheese.

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Adsorption of t h e pure milk proteins, p-casein and B-lactoglobulin, at the air/water interface has been studied using the technique of specular neutron reflectance. By fitting appropriate models of the protein films to the reflectivity data the detailed structures of the interfaces have been determined. The effects of protein concentration, substrate pH, film ageing and the presence of calcium ions on the film structures have been investigated.At neutral pH both P-casein and P-lactoglobulin form a monolayer at the air/water boundary that can be divided into a protein-rich, hydrophobic, inner layer closest to the interface, and a more diffuse, hydrophilic, outer layer extending into t h e bulk aqueous phase. The adsorbed amount of protein follows the adsorption isotherms determined by other methods. Ageing h a s little effect on P-casein layers, but with B-lactoglobulin there is an increase in the adsorbed amount of protein with time and the two-layer model of the film configuration tends to become less distinct such that a one-layer model form is equally appropriate. The rate and extent of the changes occurring as a function of the age of the surface depend on the pH of the substrate solution. The adsorbed amount of both proteins increases as the pH is lowered towards their respective isoelectric points. Models are proposed to account for t h e changes in layer structure occurring during these processes. The presence of calcium ions modifies the structure of P-casein layers, reducing the hydrophilic layer thickness and the adsorbed amount of protein.