Unveiling the synergistic effect of combining low and high frequency electric fields for microbiological safety in liquid food processing

Abstract

The synergistic effect of combining low and high radio frequency electric fields processing on Escherichia coli (E. coli) inactivation in liquid food was investigated. We show that by processing with low frequency (LF) at 12.5 kV cm−1 and 40 °C, followed by high frequency (HF) at 2.1 kV cm−1 and 65 °C, a synergistic effect on E. coli inactivation in saline water was achieved yielding approx. 5 log reduction and metabolic activity of 8.01 ± 4.34%. When similar treatment was applied to cranberry juice, an inactivation of 5.13 ± 0.21 log10 was achieved. Electron microscopy revealed that when both LF and HF treatments were applied alone, they disrupted the bacterial cell wall ultrastructure, with HF treatment additionally degrading cytoplasmic components. The sequential combination of LF and HF processes led to greater ultrastructural damage of E. coli as indicated by the observed perforation and rupture of the cell walls as well as leakage of cytoplasmic content.