Efficacy of Essential Oils on Inactivation of Escherichia coli O157:H7 in Vegetable Juice

This study was conducted to investigate the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of selected essential oils (EOs) against Escherichia coli O157:H7 under neutral and acidic pH conditions, and to evaluate the efficacy of EOs on the inactivation of E. coli O157:H7 in vegetable juice samples stored at 5, 20 and 35 degrees C or heated at 55 degrees C. The growth and survival of E. coli O157:H7 were significantly affected by pH adjustment, additive concentration, storage temperature and time. A synergistic or hurdle effect was observed within EOs at pH 4.0 and pH 4.5, or with heat treatment. The calculated decimal reduction times (D-value, min) varied with the EOs concentration. Star anise oil (0.05%, vol/vol) provided the maximum reduction in D-55 value, from 5.69 min to 0.38 min. The combination of mild heat treatment and EOs may be used to enhance the safety of juice products.