Reduction of Salmonella on Cucumbers by Washing in Thyme Oil and Thymol as Compared with Vinegar and Baking Soda

Introduction: Traditionally, most cases of salmonellosis were thought to originate from meat and poultry products. However, Salmonella spp. have been implicated in outbreaks of foodborne illness linked to the consumption of contaminated fresh produce.

Purpose: This study was designed to determine the efficacy of thymol, thyme oil, and baking soda against Salmonella on cucumbers. 

Methods: The antimicrobial activity of thymol, thyme oil, vinegar, and baking soda was tested against a three-strain cocktail of Salmonella (Salmonella Enteritidis, S. Typhimurium, and S. Mission). A 20 µl of Salmonella cocktail suspension at 10⁸ CFU/ml was spot-inoculated on the cucumbers and air-dried for 2 h prior to exposure to sanitizing solutions. Treatments included the following: thymol (0.2 and 0.4 mg/ml), thyme oil (1 and 2.0 mg/ml), vinegar (5% and 0.5 %), and baking soda (5% and 10%).  Cucumbers were dipped in the sanitizing solutions for 1, 3 and 5 minutes.

Results: On average, washing cucumbers with thymol (0.4 mg/ml); thyme oil (2 mg/ml), and vinegar (5%) for 5 min resulted in Salmonella reduction of 3.57, 3.08 log10 CFU, respectively. Thymol (0.4 mg/ml) and thyme oil (0.2 mg/ml) were most effective (P < 0.05) sanitizing solutions, which achieved >3.0 log reductions of Salmonella after a 5-min washing.  There was no significant difference (P > 0.05) in Salmonella reduction after 5-min washing in vinegar (0.5%) and baking soda (10%). Less than 1 log Salmonella reduction was achieved with 0.5% vinegar. There was no residual Salmonella in thyme washing (2.0 mg/ml), thymol (0.4 mg/ml), and vinegar (5%) solutions.

Significance: The success of this project will provide science-based information on significance of alternative treatments other than chlorine to reduce foodborne pathogens in produce, especially cucumbers.