Microstructure and Texture of Process Cheese,Milk Curds,and Caseinate Curds Containing Native or Boiled Soy Proteins

Scanning electron microscopy was used to examine the internal microstructure of process cheese, process cheese containing native soy protein, process cheese containing boiled soy protein, rennet coagulated milk curd, milk curd containing native soy protein, milk curd containing boiled soy protein, rennet coagulated caseinate curd, caseinate curd containing native soy protein, and caseinate curd containing boiled soy protein. Textural characteristics were determined with an Instron Food Testing System. Soy proteins caused the fine network microstructure of processed cheese to change to coarse porous structure. Hardness of cheese was lowered, but cohesiveness was increased by adding soy protein to process cheese. In milk curd, particles of soy protein were clustered in groups in micrographs. Cohesiveness of milk curd was lowered by native soy protein and even more by boiled soy protein. Hardness and springiness were lowered by boiled soy protein. Boiled soy protein was more extensively aggregated than was native soy protein. Soy proteins were not clearly distinguishable from casein in the micrograph of caseinate curds. Soy proteins reduced hardness and cohesiveness of caseinate curd but not as drastically as in milk curd.