Synergistic combination of physical treatments and carvacrol for Escherichia coli O157:H7 inactivation in apple, mango, orange, and tomato juices

This work has evaluated the bactericidal effect of carvacrol in combination with mild heat or pulsed electric fields (PEF) treatments to describe the treatment conditions needed to inactivate 5 log10 cycles of Escherichia coli O157:H7 cells suspended in apple, mango, orange, and tomato juices. Strong synergistic lethal effects were shown using mild heat (54 °C and 60 °C) or PEF (30 kV/cm) treatments combined with 1.3 mM of carvacrol. In relation to combinations of heat and carvacrol, the time to inactivate 5 log10 cycles of E. coli O157:H7 decreased, on average, by a 75% in apple, mango and tomato juice, and by a 84% in orange juice, or alternatively treatment temperature might be decreased up to 5 °C. With regards to PEF, while 50 exponential decay pulses at 30 kV/cm caused less than 1 log10 cell cycle reduction, the combination with carvacrol caused the inactivation of 5 log10 cell cycles by the application of 20–50 pulses as a function of the juice. The reduction of microbial contamination to 2 × 104 cells/ml allowed us to diminish the addition of carvacrol from 1.3 to the range of 0.21–0.58 mM while maintaining the synergistic effect in combination with heat or PEF. The synergism observed offers a great potential to improve traditional heat treatments by reducing treatment intensity and, thus, undesirable effects on food quality, as well as novel PEF treatments by increasing microbial inactivation in acid foods.