Chemical composition, antioxidant and antimicrobial properties of Mentha pulegium, Lavandula stoechas and Satureja calamintha Scheele essential oils and an evaluation of their bactericidal effect in combined processes

The present work investigates the chemical composition and antioxidant properties of three essential oils (EOs) (Mentha pulegium L., Lavandula stoechas L. and Satureja calamintha Scheele L.) from Morocco, and examines their antimicrobial activity as well as possible synergistic lethal effects against Escherichia coli O157:H7 and Listeria monocytogenes EGD-e in combination with mild heat or emerging methods (High hydrostatic pressure (HPP) and pulsed electric fields (PEF)). Gas chromatography–mass spectrometry (GC/MS) analysis allowed for the identification of 46 compounds as main constituents. M. pulegium EO was considerably active as an antioxidant while L. stoechas EO exhibited moderate antioxidant activity and S. calamintha L. EO showed weak activity in three complementary antioxidant tests. The evaluation of the antimicrobial effect demonstrates M. pulegium EO to be the most effective, followed by L. stoechas and S. calamintha EOs. However, the antimicrobial EO pattern changed when EOs were applied in combination with physical treatments. Low concentrations of the three EOs (0.2μL/mL) combined with mild heat (54°C/10min) or HHP treatments (175–400MPa/20min) showed effective synergistic lethal effects, inactivating up to 5 log10 cycles of E. coli O157:H7 and L. monocytogenes EGD-e, whereas combination with PEF treatments (30kV/cm/25 pulses) were much less effective. As far as we know, this is the first report on the antioxidant properties of the S. calamintha EO and on the synergistic effects of L. stoechas and S. calamintha EOs in combination with physical treatments.The bactericidal effect of EOs improves when combined with mild heat, HHP or PEF treatments. Thus, very low doses of EOs are proposed. The valuable synergistic effects observed offer great potential to improve traditional heat treatments by reducing treatment intensity and consequently adverse effects on food quality, and to enhance novel HHP and PEF treatments by achieving a higher degree of microbial inactivation.