| Use of pulsed electric fields (PEF) applied in combination with mild thermal treatments (sub-pasteurization temperatures) was investigated as a method to pasteurize fluid foods, with emphasis on preserving fluid milk. It was demonstrated that the bactericidal ability of PEF is enhanced by the simultaneous application of mild thermal treatments. A synergistic interaction between PEF and mild thermal treatments was found. A bacterial inactivation of 61og cycles of L. innocua suspended in buffer was obtained by the application of 20 pulses of 40 kV/cm at 65°C for less than 10 s, or 31 pulses of 31 kV/cm at 56°C for less than 10 s. Only three log cycles of inactivation were achieved by the application of 60 pulses of 31 kV/cm at 33°C, and five log cycles of bacterial inactivation were achieved by a thermal treatment of 66°C for 30 s. Use of a small number of pulses of the highest electric field intensity applied on milk at initial temperatures close to 55°C proved to be the most energy-efficient strategy. Application of three pulses of 40 kV/cm at 63°C for less than 10 s achieved a bacterial reduction of 4.25 log cycles with an energy expenditure of around 244 Joule/ml, which can be further reduced to 44 Joule/ml by the use of thermal regeneration. Consequently, the shelf life of milk was effectively extended for at least 24 d with the application of five pulses of 35 kV/cm at 65°C for less than 10 s, with an energy expenditure of only 82 Joule/ml. This same treatment extended the shelf life of milk for 60 or 78 d, when applied immediately after thermal pasteurization (72°C for 15 s), or after 8 d of storage following thermal pasteurization, respectively, when employed as a reprocessing strategy intended for milk delivered at remote locations where milk production is not available. Finally, it was demonstrated that the electric conductivity of the treated media, delivered electric current, and total electric energy do not play a role in defining the bactericidal effectiveness of PEF, as long as the electric field intensity, treatment time, and treatment temperature are adequately controlled. |
