The influence of moisture content on the rheological properties of processed cheese spreads

Model processed cheese spreads were prepared from rennet casein, sunflower oil, water and a trisodium citrate/citric acid chelating salt system. The samples were cooked using a laboratory-scale processed cheese cooker. The moisture content of the samples varied from 49.1 to 55.6%. The samples were characterized by dynamic rheology, rotational viscometry and fat particle size analysis. With increasing moisture content, the rheological behaviour of the samples changed from solid-like (concentrated solution) to liquid-like (dilute solution). The moduli decreased and the frequencies at which G'-G'' crossed over increased with increasing moisture content. Increasing moisture content resulted in an increase in pH and increase in the volume-to-surface diameter of the fat droplets. Rotational viscometry indicated that all the samples were shear thinning. The flow curves fitted a power law relationship (r(2) = 0.993). Thixotropic behaviour was displayed by all samples except those above 54% moisture. The shear stress at any particular shear rate increased with decreasing moisture content, indicating a stronger network structure in the low moisture samples.