Plant extracts, spices, and essential oils inactivate E. coli O157:H7 pathogens and reduce formation of potentially carcinogenic heterocyclic amines in grilled beef patties

Authors: ROUNDS, LILLIANNA - University Of Arizona; HAVENS, CODY - University Of Arizona; FEINSTEIN, YELENA - University Of Arizona; Friedman, Mendel; RAVISHANKAR, SADHANA - University Of Arizona

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2012
Publication Date: 4/25/2012
Citation: Rounds, L., Havens, C.M., Feinstein, Y., Friedman, M., Ravishankar, S. 2012. Plant extracts, spices, and essential oils inactivate E. coli O157:H7 pathogens and reduce formation of potentially carcinogenic heterocyclic amines in grilled beef patties. Journal of Agricultural and Food Chemistry. dx.doi.org/10.1021/jf204062p.

Interpretive Summary: Escherichia coli O157:H7 is the most common pathogen among the Shiga toxin-producing E. coli group. The organism was first identified in 1982 when it was isolated from people who became sick after eating undercooked beef patties from a suspected contaminated lot of meat. Since then, this foodborne pathogen has been isolated with increasing frequency from various food sources, including ground beef. Currently, E. coli O157:H7 causes about 73,000 illnesses in the United States annually. Ground beef products still remain the most common vehicle for foodborne illnesses resulting from a failure to cook meat products thoroughly. Human infection by E. coli O157:H7 is associated with a wide range of clinical manifestations, including diarrhea, hemorrhagic colitis, hemolytic uremic syndrome, and death. Inactivation of E. coli O157:H7 in beef patties is usually carried out by cooking the meat at high temperatures to eliminate the risk of foodborne illness resulting from the ingestion of undercooked meats. Previous studies indicate that this practice also increases the risk of formation of heterocyclic amines. Epidemiological studies suggest that these compounds might be associated with colon, rectal, breast, and other types of cancers in humans. The objective of this collaborative study with the University of Arizona, supported by the American Cancer Society through the Arizona Cancer Center, is to improve the microbial safety and human health. Olive extract and lemongrass essential oil were the most effective antimicrobials against E. coli O157:H7, reducing the bacterial population to undetectable levels. Olive extract and onion powder had the greatest inhibitory effects on formation of heterocyclic amines. We previously reported that onions are a rich source of antioxidative flavonoids. Our results demonstrate that the addition of plant compounds to ground beef patties has the potential to improve microbial food safety and may help prevent cancer in humans.

Technical Abstract: Meats need to be sufficiently heated to inactivate foodborne pathogens such as Escherichia coli O157:H7. High-temperature heat treatment used to prepare well-done meats could, however, increase the formation of potentially carcinogenic heterocyclic amines (HCAs). The objective of this study was to evaluate the ability of plant extracts (apple skin, grape seed, green tea, and olive), spices (cumin, garlic, oregano, paprika, and onion), and essential oils (allspice, clove bud, and lemongrass) to simultaneously inactivate E. coli O157:H7 and reduce HCAs in heated hamburger patties. Ground beef with added plant compounds was inoculated with E. coli O157:H7 (107 CFU/g). The beef was made into patties and then cooked to reach 45°C at the geometric center, flipped and cooked for 5 min. After cooling, samples were taken using for microbiological analysis and for solid-phase extraction for determination of HCAs levels using HPLC/MS. Some test substances were inhibitory only against E. coli or only against HCA formation and some inhibited both. Overall, limited or no inhibitory effects on E. coli O157:H7 were observed with the added spices, and in some cases growth was observed. Compared with grilled controls, added 5% olive or apple skin extracts reduced E. coli O157:H7 populations by 3.4 and 1.6 logs, respectively. Lemongrass oil reduced E. coli to nondetectable levels. Levels of the major HCA compounds MeIQx and PhIP were concurrently reduced with the addition of olive extract by 79.5 and 84.3%, respectively, and with apple extract by 70.7 and 82.1%, respectively. Similar results were observed with added 1% clove bud oil: bacterial populations were reduced by 1.6 logs and MeIQx and PhIP by 66.1 and 86.5%, respectively. Added onion powder decreased the formation of PhIP by 92.4%. These results suggest natural plant compounds have the potential to prevent or minimize foodborne illness and cancer in humans consuming processed meat products.