Effect of coagulation conditions on the microstructure and the large deformation properties of fat-free Feta cheese made from ultrafiltered milk

Abstract

The effects of varying rennet concentration, coagulation temperature and the time at coagulation temperature on microstructure estimated from transmission electron micrographs and on rheological behaviour measured in uniaxial compression were examined. Twelve fat-free Feta cheeses produced from ultrafiltered milk having near identical gross chemical composition were examined. High chymosin dosage, coagulation temperature, or long time at coagulation temperature leads to a coarse protein network and high values for stress at fracture in two-day-old cheese. Rate of gelation increased with both chymosin dosage and coagulation temperature. Network coarseness, propensity for syneresis and stress at fracture all showed strong relations to the rate of gelation, covering all combinations of coagulation temperature and chymosin dosage. A higher temperature or longer time at the coagulation temperature enhanced network rearrangements. In cheeses made with high chymosin dosage coagulation happened at a higher pH which also facilitated network rearrangements. In addition probably both coagulation temperature and chymosin dosage had effects on the compactness of the initial aggregates, thus contributing to the effects on microstructure and rheological properties. The two global image parameters, one measure of surface area/volume and one of the mean intercept length, both quantifying the coarseness of the protein network, were able to predict stress at fracture, the modulus and work at fracture.