Carvacrol facilates heat induced inactivation of Escherichia coli 0157:H7 and inhibits formation of heterocylic amines in grilled ground beef patties

Authors: Friedman, Mendel; ZHU, LIBIN - UNIVERSITY OF AZ, TUCSON; FIENSTEIN, YELENA - UNIVERSITY OF AZ, TUCSON; RAVISHANKAR, SADHANA - UNIVERSITY OF AZ, TUCSON

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2009
Publication Date: 2/17/2009
Citation: Friedman, M., Zhu, L., Fienstein, Y., Ravishankar, S. 2009. Carvacrol facilates heat induced inactivation of Escherichia coli 0157:H7 and inhibits formation of heterocylic amines in grilled ground beef patties. Journal of Agricultural and Food Chemistry. 57:1848-1853.

Interpretive Summary: Insufficient thermal treatment to inactivate pathogens such as E. coli O157:H7 has been considered as one of the major factors contributing to outbreaks of food poisoning following consumption of ready-to-eat meat. Meat products need to be sufficiently heated to inactivate foodborne pathogens. However, high-temperature heat treatment of ready-to-eat meats could cause a serious health concern; formation of heterocyclic amines. An increased risk of developing colorectal, breast, and other cancers may be associated with consumption of well done, fried, or barbecued meats. There is therefore a need to develop methods to cook the meats in such a way to inactivate the foodborne bacteria while concurrently reducing the formation of amines. The results of the present collaborative study (carried out at the Proteomics Laboratory, Department of Chemistry and at the Department of Veterinary Science and Microbiology, both at the University of Arizona, Tucson) demonstrate that 1% carvacrol, the main ingredient of oregano oil, added to ground beef contaminated with the virulent pathogen E. coli O157:H7 exhibits two beneficial effects. The plant compound facilitates heat inactivation of the bacteria during grilling of the patties (hamburgers) and concurrently induces reduction in the formation of heat-induced amines. These results imply that it may be possible to reduce the need to consume well-done meat. The recommended change in culinary practices will benefit microbial food safety and human health.

Technical Abstract: It has been documented that increasing the temperature of heating also induces increases in the formation of potentially heterocyclic amines in meats, which may be associated with various types of cancers in humans. But because ground beef is also susceptible to contamination by pathogenic bacteria, heating meat to the temperature at which these amines form is necessary to kill the bacteria. We theorize that addition of natural antimicrobials to the meat before heating would allow us to use lower heating temperatures to kill the bacteria, thus reducing the levels of heterocyclic amines formed. To demonstrate this possibility, ground beef was inoculated with E. coli O157:H7 and mixed well with 1% carvacrol, the main ingredient of oregano oil. Beef patties were then prepared and heat-treated on a preheated electrical skillet to reach an internal temperature of 65, 70 or 80 °C at the cold spot. Samples were then analyzed for surviving populations of E. coli by microbial assay and for heterocyclic amine levels by HPLC/MS. Multiple Reaction Monitoring (MRM) scans in positive mode were used to detect and quantitate only m/z values of the analytes of interest. Carvacrol facilitated reduction up to 100% of the bacterial population. The corresponding reduction of the three major amines was as follows: MeIQ, up to 58%; MeIQx, up to 72%; PhIP up to ~78%. The results of the present study make it possible to concurrently reduce pathogens and heterocyclic amines in a widely consumed meat product.