Inactivation of Escherichia coli O157:H7 and Salmonella on Fresh Herbs by Plant Essential Oils

Consumer awareness of fresh herbs and its demand has increased in recent years due to health benefits and distinct aroma in prepared food. There are specific markets for local growers, especially for organically grown herbs. Shiga-toxigenic Escherichia coli and Salmonella spp. have been detected and associated with foodborne outbreaks from fresh herbs. Limited treatment options are available in the processing of fresh herbs to prevent the spread of foodborne pathogens. In this study, plant-based essential oils were evaluated on fresh herbs for their antimicrobial activities against Salmonella and E. coli O157:H7. Fresh herbs (basil, cilantro, dill, parsley, and tarragon) were inoculated with cocktails of either Salmonella or E. coli O157:H7 and then dip treated with chlorine (50 ppm), cinnamaldehyde (0.3 and 0.5%), and carvacrol (0.1 and 0.3%). Control herb samples were dipped in sterile water. Samples were collected on days 0, 2, 7, and 14 for enumeration of pathogens during 4°C storage. The bactericidal efficacy differed with herbs and antimicrobial concentrations. Treatments with 0.3% carvacrol or 0.5% cinnamaldehyde reduced E. coli O157:H7 and Salmonella by 5 log CFU/g (p > 0.05%) on cilantro and dill leaves from their initial inoculum level. Bactericidal efficacy of 0.1% carvacrol and 0.3% cinnamaldehyde was significant against Salmonella compared with chlorine on all herb leaves. E. coli O157:H7 and Salmonella populations were reduced further during storage of treated herbs. There was no visual difference in herbs treated with 0.3% cinnamaldehyde or 0.1% carvacrol from control samples. Results indicate that 0.3% cinnamaldehyde and 0.1% carvacrol are effective against E. coli O157:H7 and Salmonella, retain color attributes of fresh herbs, and, therefore, may be an alternative wash treatment for fresh herbs.