Animal Science Department


First Advisor

Dennis E. Burson

Date of this Version



McCoy, A.R. 2017. Reduction of Escherichia coli Surrogates for Shiga Toxin-Producing Escherichia coli on Beef cuts by Dipping in Lactic or Peroxyacetic Acid for Short or Extended Times and the Effect on Ground Beef Quality


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science Major: Animal Science Under the Supervision of Professor Dennis E. Burson Lincoln, Nebraska, December 2017

Copyright (c) 2017 Ashley Rae McCoy


Shiga Toxin-producing Escherichia coli (STEC) are adulterants in ground beef. Antimicrobial interventions reduce STEC, but effectiveness may depend on application time and the impact on ground beef quality.

Objectives were to evaluate reductions in rifampicin-resistant E. coli (E. coliRIF) on beef clod surfaces, and the effect on ground beef quality. Beef clods were sectioned and dipped in 4.5% lactic acid (LA) or 380 ppm peroxyacetic acid (PA) for 15 or 180 s. E. coliRIF were inoculated (~5.3 log CFU/cm2) onto fat or lean tissue surfaces. Non- inoculated treatments were ground into ~454 g portions. Lipid oxidation, meat pH, APC, L* a* b*, and percentage of discoloration were all measured during retail display.

Greater reductions of inoculated E. coliRIF counts occurred with increased exposure time. The PA180 treatment had greater (P = 0.004) reductions than the control. When differing beef surfaces were treated, LA180 had lower E. coliRIF counts for APC (P < 0.0001) and E. coli petrifilms (P < 0.0001) than control treatments. Fat surfaces had greater (P = 0.024) reductions than lean on E. coli petrifilms.

Ground beef from LA treatments were not different (P > 0.05) for APC within day of display. Treatment lipid oxidation was different on days 3, 5, and 7 (P < 0.0001, P = 0.0001, P = 0.009, respectively). Ground beef pH was different on days 0, 1, and 3 (P < 0.0001, P < 0.0001, P < 0.0001, respectively). Visual percent discoloration was different on days 1, 2, and 3 (P = 0.017, P = 0.013, P = 0.042, respectively). The LA180 treatment increased lipid oxidation, decreased meat pH, and increased discoloration.

Dipping lean trim in organic acids for extended periods increases reduction of E. coli. However, excessive time reduced ground beef quality. Processors should consider quality impacts of organic acid antimicrobial interventions.

Advisor: Dennis E. Burson