Inactivation of Escherichia coli O157:H7 and Salmonella on fresh herbs by plant essential oils

Authors: Patel, Jitu; KEELARA, SHIVARAM - North Carolina State University; Green, Jennifer

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2018
Publication Date: 3/5/2018
Citation: Patel, J.R., Keelara, S., Green, J.A. 2018. Inactivation of Escherichia coli O157:H7 and Salmonella on fresh herbs by plant essential oils. Foodborne Pathogens and Disease. 15(6):1-7. https://doi.org/10.1089/fpd.2017.2377.
DOI: https://doi.org/10.1089/fpd.2017.2377

Interpretive Summary: Demand of fresh herbs has increased in recent years due to health benefits and distinct aroma in prepared food. Shiga-toxigenic Escherichia coli and Salmonella spp. have been detected and associated with foodborne outbreaks from fresh herbs. We evaluated plant-based essential oils 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%). Samples were collected on days 0, 2, 7, and 14 for enumeration of survivors during 4°C storage. Treatments with 0.3% carvacrol or 0.5% cinnamaldehyde reduced E. coli O157:H7 and Salmonella by up to 5 log CFU/g (P > 0.05%) on herb leaves from their initial inoculum level. Bacterial killing effect of 0.1% carvacrol and 0.3% cinnamaldehyde was superior to chlorine treatment; however, the difference was not significant with E. coli O157:H7. There was no color difference in fresh herbs treated with cinnamaldehyde or 0.1% carvacrol from control samples. Results indicate potential use of 0.5% cinnamaldehyde and 0.1% carvacrol as fresh herb wash to kill E. coli O157:H7 and Salmonella while maintaining the color of treated herbs. These results benefit food technologists and processors seeking nonconventional means to address pathogenic microbial contamination that may be present on commonly used fresh herb products.

Technical Abstract: 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 washed with sterile water. Samples were collected on days 0, 2, 7, and 14 for enumeration of survivors during 4°C storage. Treatments with 0.3% carvacrol or 0.5% cinnamaldehyde reduced E. coli O157:H7 and Salmonella by up to 5 log CFU/g (P > 0.05%) on herb leaves from their initial inoculum level. Bactericidal efficacy of 0.1% carvacrol and 0.3% cinnamaldehyde was superior to chlorine treatment; however, the difference was not significant with E. coli O157:H7. Further, the bactericidal effect of these oils varied with herb. The reduction of these pathogens by essential E. coli O157:H7 and Salmonella populations were reduced further during storage of treated herbs. There was no visual difference in herbs treated with cinnamaldehyde or 0.1% carvacrol from control samples. Results indicate that 0.5% cinnamaldehyde and 0.1% carvacrol are effective against E. coli O157:H7 and Salmonella, may also retain sensory attributes of fresh herbs, and therefore, may be an alternative wash treatment for fresh herbs.