Antibacterial Efficacy of Eugenol against Escherichia coli O157:H7 and Salmonella enterica in Unpasteurized Apple Juice Produced in Juice Bars and Held at 4°C

Introduction:  Growing consumer demand for minimally processed foods devoid of synthetic preservatives has fueled increased consumption of unpasteurized juices produced in juice bars. Juice bars do not apply a kill step for pathogens and unpasteurized juices have been implicated in several foodborn disease outbreaks.

Purpose: The purpose of this study was to examine the antibacterial effect of eugenol, a component of clove oil, against Escherichia coli O157:H7 and Salmonella enterica in refrigerated, unpasteurized apple juice.

Methods: Unpasteurized apple juice with added eugenol (0.25, 0.5, and 1.0 μl/ml), was inoculated with a 5-strain mixture of E. coli O157:H7 or S. enterica to obtain an initial viable count of 7.0 log CFU/ml. Juice without added eugenol served as control. Viability of pathogens in the juices (4°C), at set times during 24 hours, was evaluated by plating diluted (10-fold) juice samples on sorbitol MacConkey agar (E. coli O157:H7) and xylose lysine tergitol 4 agar (S. enterica) and counting bacterial colonies on agar media after incubation (35ºC, 48h).

Results: In juice with or without added eugenol, no growth of the pathogens occurred at 4ºC. Viable pathogens in control juice decreased by approximately 0.7 to 1.0 log CFU/ml at 24 h. Salmonella enterica was more sensitive to eugenol (1.0 μl/ml) compared to E. coli O157:H7. In juice containing eugenol at 0.25 μl/ml, viable E. coli O157:H7 and Salmonella decreased by approximately 3.62 and 4.24 log, respectively, after 4 h. Eugenol (0.5 or 1.0 μl/ml) inactivated both pathogens by more than 5.0 log after 4 h and none of the pathogens was detected after 24 h in juice with the same eugenol concentrations (P <0.05).

Significance:   Eugenol has good potential for use as a natural antimicrobial for inactivating bacterial pathogens in refrigerated unpasteurized apple juice.