Coagulation of milk enriched with ultrafiltered or diafiltered microfiltered milk retentate powders

Rennet coagulation of milk with a total protein content of 3.5% (control) was compared to milk enriched to 4, 4.5 or 5% total proteins with a regular ultrafiltered milk retentate (RUF) powder obtained by spray drying, a diafiltered microfiltered milk retentate (DMF) powder and an acidified diafiltered microfiltered milk retentate (ADMF) powder obtained by freeze-drying. The protein to fat ratio for each milk was adjusted to 0.95. Evolution of milk coagulation was followed by a turbidity method. The coagulation parameters measured were: the lag time (T-lag), the time at inflexion point (T-max), the rate of increase (D-max), the optical density ratio at infinite time (ODinfinity), and the gel firmness (GF). The effect of adding CaCl2 (0.00, 0.01 or 0.02%) was also investigated. In all cases, enriched milk had different coagulation properties than control milk. The GF and coagulation parameters increased as the protein concentration in milk increased. The use of DMF powder to enrich milk modified the coagulation parameters more than the use of RUF powder. However, this effect was reduced by using ADMF powder, which contained less mineral than DMF powder. The time parameters, T-lag and T-max, for DMF milk were shorter than those measured for control, RUF and ADMF milk. In addition, D-max, ODinfinity and GF for DMF milk were higher than those determined for control, RUF and ADMF milk. Differences observed between coagulation parameters of individual enriched milk types were reduced by addition of CaCl2. (C) 1997 Elsevier Science Ltd. All rights reserved.