Influence of the protein content on structural characteristics of stirred fermented milk

Milk proteins are the major constituents modified during the manufacture of fermented dairy products, such as yogurt and fresh cheese. The aim of the study was to observe the influence of protein concentration on the structur al characteristics of stirred fermented milk. The experiments were conducte d in order to establish the connections existing between rheological proper ties and the microstructure of stirred fermented milk. Increasing the prote in concentration of skim milk by means of nanofiltration from 3.5 to 7.0% l ed to firmer gels and to a higher viscosity and serum-holding capacity of t he stirred fermented products; even the degree of solvation was increased. These structural properties and electron micrographs indicate that the high er the protein concentration, the finer the gel network. In contrast, the a ddition of rennet at the beginning of the fermentation induced a coarser ne twork. Therefore, the gels made by acidification and rennet action are firm er and the stirred products hold less serum; however, the apparent viscosit y is higher compared to stirred products made by acidification.