Pasteurization is a mild heat treatment designed to reduce the number of pathogenic microorganisms in food to a level that does not cause illness, while minimizing changes to nutritional and sensory properties. The two primary regimes are high-temperature short-time (HTST) and low-temperature long-time (LTLT). HTST uses temperatures around 72°C for 15 seconds for milk, achieving a 5-log reduction of Coxiella burnetii as the target pathogen. LTLT operates at 63°C for 30 minutes and is still used for some specialty products.
The thermal death kinetics are characterized by three key parameters: the D-value (time required for a 1-log reduction at a given temperature), the z-value (temperature change required to alter the D-value by a factor of 10), and the F-value (the integrated lethal effect expressed as equivalent minutes at a reference temperature). Pasteurization units (PU) are calculated to ensure sufficient lethality, typically defined as one minute at 60°C with z = 6.7°C for milk. Enzyme inactivation tests, particularly the alkaline phosphatase test for milk, provide a rapid verification of proper pasteurization.
Applications span numerous food categories. Milk and dairy products are the most common, but pasteurization is also applied to fruit juices (93°C for a few seconds for Alicyclobacillus control), beer (72°C for 30 seconds or tunnel pasteurization of bottled beer), liquid eggs (57°C for 3 minutes), and certain canned fruits. The heat treatment inevitably causes some nutrient losses: vitamin C degradation can reach 10-25% in milk, and thiamine losses occur in acid products. However, these losses are generally acceptable relative to the safety benefits.
Process validation involves heat penetration studies, temperature distribution mapping, and microbiological challenge testing. Continuous flow pasteurizers require careful flow rate control, pressure differentials to prevent raw product contamination, and proper data logging. Modern systems incorporate regenerative heating sections that recover up to 95% of heat energy. Pasteurization is less severe than commercial sterilization and is distinct from blanching, which targets enzyme inactivation. UHT processing achieves extended shelf-life through higher temperatures.
