Milk protein-carrageenan interactions

Factorial experimental designs were employed to study the major factors governing the gelation of milk/kappa-carrageenan mixtures. The relative effects of carrageenan concentration, pH, ionic strength, casein proteins, whey proteins and kappa-casein genotype on the mechanical properties of the gels were studied using dynamic rheological techniques. Gel transition temperature was governed mainly by ionic strength and carrageenan concentration whilst gel strength was influenced by carrageenan concentration and pH. It was found that the relative importance of the milk proteins to gelation varied with carrageenan concentration. It appeared that at high levels of kappa-carrageenan (i. e. 0.1% w/w) gelation was predominately the result of association of kappa-carrageenan helices to produce self-supporting gels. Milk proteins appeared to have little effect at high levels of carrageenan. However, milk proteins interfered with gel formation at carrageenan concentrations lower than 0.018% w/w, thus increasing the amount of micellar casein by twofold inhibited gelation. Serum proteins also suppressed gelation, albeit at lower kappa-carrageenan concentrations. These results suggested that, in the presence of milk proteins, gel formation involved mainly carrageenan-carrageenan cross-linkages and not carrageenan-casein or casein-casein linkages. Nevertheless, the possibility of a strong interaction between kappa-carrageenan and kappa-casein on the micelles which has to be satisfied first, leaving insufficient carrageenan to provide network forming capability, cannot be ruled out.