Changes in the quality of recombined UHT milk processed by direct and indirect heating system during storage

College of Agriculture, Food Science Department, King Saud University, Riyadh, Saudi ArabiaThe changes in quality of recombined ultra high temperature (RUHT) milk processed by indirect (R[UHT and R2UHT) and direct (R3UHT) systems were investigated during storage at 20° and 35°C. The changes in acidity, pH, fat separation, proteolysis, lipolysis (ADV), viscosity, sedimentation, milk reducing substances (MRS) and sensory characteristics were followed. All RUHT milk samples showed significant changes in most characteristics studied. The extent of changes increased with storage time and temperature. The rates of changes in acidity (TA) and pH were similar. RI UHT and R2UHT milks showed lower fat separation which was probably due to higher homogenization efficiency and the quantity of the added stabilizer-emulsifier. The rate of changes in MRS, ADV and viscosity was lower in R3UHT milk. However, sedimentation and proteolysis were lower in RI UHT and R2UHT milks (indirect pro-cess). In general, the differences in acceptability might be attributed to the extent of lipolysis and Maillard reaction in RI UHT and R2UHT milks. The results showed a gradual deterioration of the quality of RUHT milk on storage at high temperature. Therefore, RUHT milk should be stored in air-conditioned storage during the hot months of summer