The Role of Proteases in the Stability of UHT-Treated Milk

Ultra-high temperature (UHT) treatment of milk is a continuous process whereby milk is heat-treated at 135–150 °C for holding periods of 0.2–20 s, to produce a commercially sterile product that may only contain viable thermophilic bacterial spores, but in which bacterial growth is highly unlikely to occur under normal storage conditions. UHT treatment is typically combined with aseptic packaging, which involves filling the UHT-treated milk into sterile containers in a sterile atmosphere and sealing the containers in a sterile method in a continuous process which allows the UHT milk to remain bacteriologically stable at ambient temperatures for at least 6 months. According to European Commission Regulation (EC) 2074/2005, a UHT milk treatment must be “sufficient to ensure that the products remain microbiologically stable after incubating for 15 days at 30 °C in closed containers or for 7 days at 55 °C in closed containers or after any other method demonstrating that the appropriate heat treatment has been applied”.