A schematic model was proposed to account for these observations. The variation in apparent viscosity with apparent diameter of casein micelles was found to be greater at low shear rates. The main effect of preheat treatments during manufacture on the rheology of MPC85 solutions was the linear increase in apparent viscosity with apparent diameter of casein micelles. In reconstituted solutions the apparent diameter of the casein micelles increased gradually with heat treatments up to 86% WDN and dramatically at higher WDN levels. The variations in rheology and rennet coagulation properties among the pilot plant powders were found to be correlated with the apparent diameter of the casein micelles. Heat treatments resulting in ≥90% WDN produced a dramatic loss in heat stability. Heat treatment had no effect on heat stability of reconstituted MPC85 solutions for whey protein denaturation (WDN) values up to 86%. The effect of preheat treatments during the pilot-scale manufacture of MPC85 on functionality was investigated. The rheological properties of MPC85 were profoundly influenced by the presence of any insoluble solids. The solubility of commercial MPC85 was found to be dependent on the temperature at which the solution was prepared, increasing from ≈59% at 20☌ to 100% at 50☌ Homogenisation was shown to improve the solubility of MPC85 at 20☌. At lower temperatures (15% w/w total solids) were pseudoplastic and did not possess a yield stress.
These solutions were also found to be Bingham Plastics. At low concentrations (15% w/w total solids) the logarithm of apparent viscosity was found to increase linearly with protein concentration. The rheological properties of reconstituted commercial MPC85 were studied at various temperatures and concentrations. The flow behaviour of the concentrate was adequately described by a Power Law rheological model. This result is the opposite of skim milk concentrate which age-thickens at evaporator temperatures.
A rheological study of milk protein concentrate (52☌) prior to spray drying showed a slight age-thinning behaviour which lasted about one hour, after which the apparent viscosity of the concentrate remained constant. The aim of this thesis was to explore aspects of the functional properties of MPC85 (milk protein concentrate, 85% protein).