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

摘要

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 mum, pressure; 225 kPa) at two temperatures (37 degrees C or 55 degrees C), before being immediately treated with PEF (electric field strength; 32 kV/cm, pulse width; 10 mus, frequency; 320 Hz). Thermal pasteurisation (72 degrees 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 degrees C and 55 degrees 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