Antibacterial Efficacy of Geraniol against Escherichia coli O157:H7 and Salmonella enterica in Carrot Juice and a Mixed Berry Juice Held at 4°C

Introduction: Growing consumer demand for foods that are free of synthetic preservatives has generated much interest among food processors to use naturally-derived antimicrobials for controlling foodborne pathogens.

Purpose: A study was performed to investigate the antimicrobial efficacy of geraniol, a plant-based extract, against Escherichia coli O157:H7 and Salmonella enterica in refrigerated (4 ºC) carrot juice (CRJ) and a mixed berry juice (MBJ).

Methods: Carrot juice (pH 6.3, 8.5°Brix) and MBJ (pH 3.6, 12.3°Brix) with added geraniol at 0.5 to 1.5 or  2.0  μl/ml were inoculated with a 5-strain mixture of E. coli O157:H7 or S. enterica to obtain an initial viable count of 5.08 log₁₀ CFU/ml. Inoculated juices without geraniol served as control.  Numbers of viable pathogens in the juices held at 4°C for 24 hours were monitored by surface 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 after incubation (35°C, 48 h).

Results: None of the pathogens grew in the refrigerated (4 ºC) juices with or without added geraniol.  In control juices, pathogen viability decreased by ~1.15 to 1.33 log₁₀ CFU/ml after 24 h. Both pathogens were more sensitive to the antibacterial effects of geraniol in MBJ compared to CRJ.  Initial viable counts of S. enterica and E. coli O157:H7 in CRJ with 2.0 μl/ml geraniol decreased by ~4.56 - and 4.25 log, respectively, after 24 h (P < 0.05).  In contrast, just after 1 h, a lower concentration of geraniol (1.0 μl/ml) completely inactivated both pathogens (negative enrichment test) in MBJ (P < 0.05). 

Significance: Geraniol has good potential for use as a natural antimicrobial to destroy human enteric pathogens in refrigerated carrot or berry juice.