Potential of thyme essential oil on arugula sanitization

Abstract

Essential oils from plants are an important alternative source of antimicrobial compounds against important pathogens for food safety. This study aimed to evaluate the in vitro antimicrobial activity of thyme essential oil (Thymus vulgaris) and to apply it in the sanitization of minimally processed arugula (Eruca sativa), aiming to increase the safety and shelf life of arugula. The in vitro antibacterial activity of the essential oil was evaluated by disc diffusion assays and determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against different foodborne pathogens. Thereafter, a “challenge test” was carried out to evaluate the antibacterial activity of the thyme essential oil (0.2%) on the sanitization of arugula inoculated with Escherichia coli (3 log CFU mL-1) compared to sodium hypochlorite (120 ppm of active chlorine). Afterwards, an experiment of applying the thyme essential oil (0.2%) as a sanitizing agent in minimally processed arugula was carried out to evaluate the vegetable shelf life compared to sodium hypochlorite (120 ppm of active chlorine). The arugula was stored at 8 °C for 7 days, and periodically, the number of aerobic mesophilic microorganisms, pH and titratable acidity were determined, and the color of the samples was evaluated. The thyme essential oil had strong antimicrobial activity in vitro against all species of bacteria tested. In the experiments in situ, the thyme essential oil (0.2%) and sodium hypochlorite (120 ppm of active chlorine) were not efficient in eliminating the inoculated E. coli from minimally processed arugula, and they did not result in an extension of the shelf life of the arugula in comparison to the control (p>0.05). However, the growth rate of the E. coli population over time on the arugula samples sanitized with the thyme essential oil (0.2%) was low, which indicates a positive effect of the essential oil, which may be optimized with future adjustments in the concentration and immersion time for the arugula sanitization.