Electron Microscopic Studies of Casein Micelles and Curd Microstructure in Cottage Cheese

Electron microscopy was employed to follow changes in the casein micelles in milk through gelling and cooking. Scanning electron microscopy showed that casein micelles aggregated into chains, then strands and clusters, and eventually into amorphous masses. There was a decrease in porosity along with an increase in size of casein aggregates throughout the manufacturing process. Based on measurements of particles in transmission electron micrographs, casein micelles or fused particles increased in size during curd manufacture in three significantly different stages—in milk, during gelling and healing, and during cooking. Data, corrected by a statistical technique which accounted for all transmission electron microscopy slices not having been obtained through the micelle diameters, yielded average diameters of micelles of 87.6nm in milk, 181.6nm during early gelling, 184.9nm at the end of healing, 206.1nm during cooking, and 207.6nm at the end of cooking. Acid and culture set curds showed similar microstructures.