Effect of High Pressure Homogenization Process on Bacillus Stearothermophilus and Clostridium Sporogenes Spores in Skim Milk

Abstract

High pressure homogenization (HPH) is an alternative food processing technique. As product heating is minimum, its characteristics are not affected in a large extend. This characteristic makes the HPH an interesting process to guarantee the safety of thermo-labile food. Inactivation of Bacillus stearothermophilus ATCC 7953 and Clostridium sporogenes PA 3679 spores in skim milk by HPH was studied. Results showed that pressures up to 300 MPa were not able to cause any reduction on spore counts or promote changes on its thermal resistance. The application of heat shock (100°C/15 min) before HPH treatment and the homogenization process realized at mild inlet temperature (45°C) – which results in homogenization temperature of around 84°C at 300 MPa - also did not cause reduction on viable spores counts. A few spores reduction (0.67 logarithmic cycles) were only observed when the milk samples were subjected to homogenization treatment 16 times (multiple passes) at 300 MPa. Therefore, although HPH be recognized as an effective method for milk pasteurization, it was conclude that the HPH process is not able to guarantee the commercial sterility of milk, being necessary the association of the homogenization with another preservative method, as refrigeration.