Combined treatment with mild heat, manothermosonication and pulsed electric fields reduces microbial growth in milk

In recent years, there has been considerable interest in non-thermal milk processing. The objective of the present study was to assess the efficacy of two non-thermal technologies (manothermosonication; MTS, and pulsed electric fields; PEF) in comparison to thermal pasteurisation, by assessing the microbial levels of each of these milk samples post-processing. Homogenised milk was subjected to MTS (frequency; 20kHz, amplitude; 27.9μm, pressure; 225kPa) at two temperatures (37°C or 55°C), before being immediately treated with PEF (electric field strength; 32kV/cm, pulse width; 10μs, frequency; 320Hz). Thermal pasteurisation (72°C, 20s) was included as a control treatment. Microbial content of each milk sample was monitored over a 21-day period. It was determined that milks treated with MTS/PEF at 37°C and 55°C contained lower microbial levels than raw milk for a certain duration, but after 14 days milk which had been pasteurised by conventional methods contained significantly (P<0.05) less microorganisms. However, milks treated with MTS/PEF contained significantly (P<0.05) fewer microorganisms than raw milk at each time point. Although not as effective as pasteurisation, the present study demonstrates the ability of MTS/PEF treatment to reduce microbial content of milk, while avoiding prolonged heat exposure to temperatures such as those used during conventional (thermal) pasteurisation.