Small strain oscillatory shear and microstructural analyses of a model processed cheese

The rheological and microstructural properties of a model processed cheese were investigated. The cheese contained 20% protein (rennet casein), 27% anhydrous milk fat, 1.5% NaCl and 1 to 3% Na2HPO4 (DSP). Processing time (10, 20, or 30 min), DSP (1, 2, or 3%) and pH of the DSP-NaCl solution (5.4, 5.6, or 5.8) were adjusted to alter rheological properties. Small-strain oscillatory shear rheological parameters that correlated with transitions previously observed by large-strain (fracture) properties were moduli at 8 degrees C and changes in moduli with cooling from 80 to 25 degrees C. Mechanical spectra at 80 degrees C indicated cheeses containing less than 2.0% DSP were entangled macromolecular dispersions, and those containing more than 2.0% DSP were gels. A compilation of small strain results suggested samples could be divided into three basic rheological states. A model describing the gel network is proposed based on the results of this investigation and large-strain (fracture) rheological properties. The model was based on increased breakdown of para-casein aggregates into amphiphilic molecules and rheological properties being related to the combination of para-casein aggregates and amphiphilic molecules.