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

- Milk was processed with MTS/PEF at two temperatures (37 °C & 55 °C).
- The microbiological content of these milks was assessed over a 21 day period.
- Thermally pasteurised milk was included as a control.
- MTS/PEF-treated milk contained significantly (P < 0.05) fewer microorganisms than raw milk.
- Results show that MTS/PEF reduces microbial content without excessive levels of heat.

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; 20 kHz, amplitude; 27.9 μm, pressure; 225 kPa) at two temperatures (37 °C or 55 °C), before being immediately treated with PEF (electric field strength; 32 kV/cm, pulse width; 10 μs, frequency; 320 Hz). Thermal pasteurisation (72 °C, 20 s) 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.