Inactivation of Escherichia coli O157:H7 in fruit juices by combined treatments of citrus fruit essential oils and heat

This work approaches the possibility of combining mild heat treatments with citrus fruit essential oils (EOs) to improve the effectiveness of heat treatments and thus to reduce treatment intensity. Concentrations between 10 and 200 μL/L of lemon, mandarin, or orange EO were tested at 54 °C for 10 min in laboratory media, determining that 200 μL/L of each EO was necessary to achieve a 5 log10 reduction of the initial Escherichia coli O157:H7 concentration. A relationship could be established between sublethally injured cells after the heat treatment and inactivated cells after the combined process. In apple juice, the synergism in the inactivation of E. coli O157:H7 when adding 200 μL/L of lemon EO might suppose a reduction in the treatment temperature (of 4.5 °C) or in the treatment time (by 5.7 times) within the range of temperature assayed (54–60 °C). Addition of 75 μL/L of lemon EO was determined to achieve the same synergistic effect of the combined treatment when the initial inoculum was reduced from 3 × 107 to 3 × 104 CFU/mL. Since the addition of lemon EO did not decrease the hedonic acceptability of apple juice, the proposed combined treatment could be further studied and optimized for the production of new minimally processed juices.