The Casein Micelle: Stability And Heat Induced Interactions
The increasing availability of micellar casein obtained by membrane separation creates a need to better understand the effect of processing conditions, on the stability and properties of this ingredient. This work focused on studying the heat-induced interactions in micellar casein concentrates, and in micellar casein (MCN)-soy protein (SP) blends. These changes were investigated using a range of physical measurements (zeta potential and particle size measurements, rheological analyses) and chemical analyses (compositional, differential solubility and Native-PAGE analyses). First, heat induced effects on the properties of micellar casein (MCN)-soy protein (SP) blends (1:1 ratio) were evaluated. Individual and mixed protein systems of 2.5% - 15% concentration were subjected to temperatures between 40[MASCULINE ORDINAL INDICATOR]C - 95[MASCULINE ORDINAL INDICATOR]C. Heat treatments at T[GREATER-THAN OR EQUAL TO]80[MASCULINE ORDINAL INDICATOR]C induced soy protein (glycinin) denaturation, which resulted in protein aggregation and network formation by disulfide bonding, when soy protein content >6.3%. There was no evidence of cross-linking between soy proteins and casein micelles, as disulfide bonding seemed to occur exclusively between soy protein molecules. In MCN-SP mixtures with soy protein content <6.3%, thermal denaturation of soy proteins induced local phase separation between the casein micelles and the soy protein molecules. This resulted in protein mixtures with low shear viscosity, Newtonian flow behavior and very good stability to sedimentation. In the second part, the effect of commercial sterilization (UHT - ultra high temperature - treatment and retorting) on micellar casein concentrates (MCC) of 5% 10% casein concentration was evaluated. Sterilization affected the stability, viscosity and flow behavior of MCCs, mainly due to loss in solubility of calcium phosphate at the micelle level. Retorting resulted in slight aggregation of casein micelles, while UHT caused the formation of visible aggregates. The UHT treated MCCs had higher viscosity than retorted MCCs, and displayed a solid-like behavior, indicative of structure formation. Drying of MCCs affected their sterilization behavior, as reconstituted micellar casein concentrates (R-MCCs) were more unstable to UHT sterilization than MCCs. The calcium concentration per gram of casein was identified as critical parameter for the heating stability of MCCs. This work provides critical information for developing commercial applications of micellar casein, as well as micellar casein-soy mixtures.
Micellar Casein; Heat Treatments; Dynamic Light Scattering; Rheology; Soy Proteins; Sterilization; Minerals
Moraru, Carmen I
Rizvi, Syed S H; Bendaniel, David J.
Food Science & Technology
Ph.D. of Food Science & Technology
Doctor of Philosophy
dissertation or thesis