Antimicrobial Activity of Marjoram (Origanum Majorana) Essential Oil Against the Multidrug-Resistant Salmonella Enterica Serovar Schwarzengrund Inoculated in Vegetables from Organic Farming

Antimicrobial efficacy of the marjoram essential oil (MEO) on organic vegetables inoculated with 4 log/cfu Salmonella enterica serovar Schwarzengrund was evaluated. Previously inoculated samples of smooth lettuce (Lactuva sativa), kale (Brassica oleracea) and arugula (Eruca sativa) were immersed, separately, in three MEO solutions (0.1, 0.3 and 0.5%) for 1 and 2 min. Control groups with sterile phosphate-buffered saline and sodium hypochlorite (250 ppm) solution were also used. The enumeration of Salmonella was performed for 3 consecutive days, and the essential oil yielded an average reduction in microbial load, ranging from 2.12-3.31 log/cfu, in all samples, against 1.86-2.81 log/cfu obtained by the traditional disinfection method with hypochlorite solution. In lettuce samples, the 0.5% MEO concentration showed similar efficacy to the hypochlorite control. The same concentration of essential oil tested in kale and arugula showed significant antimicrobial activity when compared to the same control. Sensory and affective tests showed good acceptability of the MEO flavor on lettuce leaves. According to this experimental model, this oil has promising antimicrobial activity against Salmonella enterica serovar Schwarzengrund and may be used to reduce or replace sodium hypochlorite during the disinfection process of vegetables. Practical ApplicationsThe marjoram essential oil at 0.5% concentration showed potential application in the disinfection process of vegetables for human consumption. Its disinfection capacity against a high concentration of multidrug-resistant Salmonella enterica serovar Schwarzengrund was similar or even better than the sodium hypochlorite solution commonly used to remove or reduce the microbial load of fresh vegetables or similar foods.