Combined pulsed electric field and high-power ultrasound treatments for microbial inactivation in oil-in-water emulsions

The impact of individual and combined pulsed electric field (PEF) and high power ultrasound (HPU) on the inactivation of different microorganisms in emulsions was investigated. The highest inactivation level using PEF was 2.6, 1.2 and 0.1 log-cycles for Escherichia coli, Aspergillus niger and Bacillus pumilus, respectively, achieved at the highest energy level and temperature (152.3-176.3 kJ/kg and 25 degrees C). HPU led to the highest reduction (5.4, 4.3 and 0.3 log-cycles for E. coli, A. niger and B. pumilus, respectively) after the longest treatment time studied (3 min). PEF (152.3-176.3 kJ/kg) followed by HPU (3 min) was found to be the most effective sequence, leading to synergistic effects (6.6 and 1.0 log-cycles for A. niger and B. pumilus, respectively), compared to the individual treatments. PEF-HPU is a promising hurdle technology with which to inactivate vegetative bacteria or fungal spores in emulsions. However, limited inactivation was achieved for bacterial spores.