Bacterial inactivation in whole milk using pulsed electric field processing

Inactivation of Gram-negative and Gram-positive bacteria in whole milk by pulsed electric field (PEF) processing with pre-heating of milk and stepwise intermediate cooling was compared with thermal pasteurisation. Electric field strengths of 18–28 kV cm−1 for 17–235 μs were applied to milk at different temperatures for 24 s. PEF treatment at 4 °C did not reduce bacterial numbers, but the effectiveness increased with increasing temperature. PEF treatments at 22–28 kV cm−1 for 17–101 μs at 50 °C gave a 5–6 log reduction, below the detection limit for Pseudomonas aeruginosa, while Escherichia coli, Staphylococcus aureus and Listeria innocua were reduced to below the detection limit at 55 °C. Gram-negative bacteria were less resistant to PEF than Gram-positive bacteria. PEF treatment with stepwise intermediate cooling after pre-heating at 55 °C for 24 s at a flow rate of 4.2 mL s−1 has the potential to pasteurise whole milk.