Antimicrobial Effectiveness of Eugenol or Geraniol Alone or Combined against Escherichia coli O157:H7 and Salmonella enterica in Pineapple Juice Held at 4°C

Introduction: Plant essential oils (EOs) and several of their components exhibit antimicrobial effectiveness against foodborne pathogens; however, their use at effective levels in foods is largely limited by negative sensory changes. Application of EO components in combination may result in lower effective antimicrobial concentrations.

Purpose: A study was performed to evaluate the antimicrobial efficacy of eugenol or geraniol alone or combined against Escherichia coli O157:H7 and Salmonella entericain refrigerated (4 ºC) pineapple juice.

Methods: Commercial pineapple juice (pH 3.4) containing 0.0 (control), 0.125, 0.25 or 0.50 μl/ml of each EO component (eugenol or geraniol) or dual-combinations containing 0.125 μl/ml of each component, were inoculated with 7.99 log CFU/ml of E. coli O157:H7 or 7.78 log CFU/ml S.entericaand stored at 4 ºC. Survivors were determined after 0, 1, 2, 4, 8 and 24 h by surface plating diluted (10-fold) juice samples on tryptic soy agar supplemented with 0.6% yeast extract and counting bacterial colonies after incubation (35°C, 48 h).

Results: No growth of either pathogen occurred in the refrigerated (4 ºC) juice with or without added antimicrobial. After 24 h, treatments with 0.50 μl/ml geraniol alone resulted in > 5 log CFU/ml reductions of both pathogens. Initial viable counts of S. enterica and E. coli O157:H7 in juice with 0.50 μl/ml geraniol decreased by ~ 7.78 log and 7.29 log, (P < 0.05) respectively, after 24 h; log reductions in juice with eugenol at 0.50 μl/ml were 3.45 (S. enterica) and 2.14 (E. coliO157:H7). Eugenol and geraniol combined (each at 0.125 μl/ml) eliminated ~ 1.91 log (E. coli O157:H7) and ~ 2.75 log (S. enterica) after 24 h.

Significance: Geraniol has good potential for killing enteric pathogens in pineapple juice.