Flow and structural characteristics of concentrated milk

The flow and structural characteristics of concentrated milk were analyzed between concentrations of 12.5 and 46.7% solids content at room temperature . The rheological behavior of milk concentrates was represented by paramete rs corresponding to Newtonian, Power Law, or Herschel-Bulkley equations dep ending on the solids content level. The resulting flow behavior indices and consistency coefficients were correlated to concentration by a single-term exponential equation, with only milk concentrates above 40% solids content exhibiting yield stress. Milk concentrates were characterized by scanning electron microscopy (SEM), complemented by transmission electron microscopy (TEM) and image analysis (IA). Casein micelles appeared as granular partic les (0.1-0.3 mu m) with a rough surface. Fat globules, noted as small holes in the SEM pictures, appeared to be major spherical components (0.5-10 mu m) in the transmission electron microscope images as well as in the image a nalysis inverted micrographs. Fat globules in the milk concentrates were su rrounded by a membrane which was thicker in the concentrated milk than in t he fresh milk. TEM images were very helpful in observing the interparticle interactions, as well as the thickness of the fat membranes that corroborat ed with the SEM observations. The IA pictures allowed the identification an d characterization of the fat globule features.