Project Summary

Characterization of Growth Potential of Escherichia coli O157:H7 in Irradiated Beef Patties and Effect of Packaging Material

Principle Investigator(s):
E.A. Murano, P.S. Murano, G.R. Acuff and J. Dickson
Texas A&M University and Iowa State University
Completion Date:
March 1998


Layman’s Summary 

This study was designed to evaluate whether current packaging systems being used in the meat industry result in any changes in the ability to inactivate E. coli O157:H7 after irradiating ground beef and what effect these materials have on the quality of the product. It is currently known that packaging interaction with oxygen can cause free radicals and off odors/flavors to form in ground beef after irradiation.  Higher dose rates of irradiation may in fact reduce free radical formation due to the depletion of oxygen. However, oxygen does play a role in the inactivation of bacteria during irradiation. 

Ground beef was inoculated with E. coli O157:H7, formed into patties and then packaged into one of three commercially available packaging systems 1) nylon/polyethylene 2) Saran overwrap or 3) Saran/polyester/polyethylene. These 3 bag types represent variable moisture and oxygen permeability. The bags were sealed in air or under vacuum. Samples were then irradiated in both fresh and frozen form and subjected to a range of doses using either electron beam or gamma ray irradiation. After irradiation was complete, the samples were sent back to the laboratory for enumeration of E. coli O157:H7 survivors.   

There was no effect of packaging material or atmosphere on the D10 values, which are values representing the amount of irradiation dosage needed for the inactivation of certain levels of E. coli O157:H7, regardless of which type of irradiation source was used. Frozen patties required higher levels of irradiation (D10) for inactivation of E. coli O157:H7 than for fresh patties.  

It was also noted that in this study, the presence of oxygen played a key role in the inactivation of E. coli O157:H7 and this was especially true at the lower dose levels. Only one significant effect was found in the sensory evaluations between control and irradiated ground beef patties, and that was a stronger cooked beef/broth flavor in control patties.   

The fact that no dose-rate effect was found on fresh patties in this study suggest that there are multiple factors that must be in place for dose rate to influence bacterial survival to irradiation. This highlights the need for further study of factors that affect pathogen survival during irradiation. Note: This report does not contain the results from the final objective and should be included as an addendum later.