Changes in the Quality of Fresh and Recombined Ultra High Temperature Treated Milk During Storage

The quality of fresh ultra high temperature treated (FUHT) milk and recombined ultra high temperature treated (RUHT) milk and the changes in their quality during storage at 6, 20 or 35 degrees C were examined. FUHT and RUHT milks were processed similarly, except for homogenization. Both milks underwent excessive fat separation, but it was less in RUHT milk than in FUHT milk, due mainly to higher homogenization efficiency and the addition of stabilizer-emulsifier to the former. Most FUHT and R UHT milk samples showed significant changes in all characteristics studied. The extent of the changes increased with storage time and temperature, except for the viscosity of RUHT milk, which increased more at low temperature. The rates of change in pH, milk reducing substances and sensory quality were higher in RUHT milk than in FUHT milk. However, the rates of change in titrable acidity, AD V, proteolysis and sedimentation were similar in both types of milk. The major causes of low sensory quality of stored RUHT milk were non-enzymatic browning and lipolysis. In general, the quality of UHT milk stored under hot climatic conditions might not be acceptable after 6 months. Therefore, storage in air-conditioned stores or reduction of the UHT milk storage period is recommended.